• Volume 36,Issue 1,2014 Table of Contents
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    • Seismic Fragility Analysis of Steel Structure Considering Steel Corrosion

      2014, 36(1):1-6.

      Abstract (2533) HTML (0) PDF 11.48 M (3685) Comment (0) Favorites

      Abstract:Steel frames not only have the advantages of being light weight,and high strength but also are corrosion resistant and fireproof,so steel is widely used for industrial construction.Unfortunately,research on corrosion mechanisms and measures of corrosion protection were mainly aimed at the timber level and based on experiments.Due to differences in test conditions,test methods and other factors,conclusions from these experiments were highly variable and empirical formulas were difficult to utilize.In addition,research aimed at component-level corrosion was also not yet clear,so uniform corrosion is often assumed for convenience.For example,some simply reported weakened cross-section members and considered material deterioration to analyze structural performance. In this paper,we consider the seismic performance of overall structure in different service times.Material deterioration and non-uniform corrosion were accounted for in column and beam cross-sections.Steel corrosion caused the deterioration of seismic performance and stiffness for structures.When steel frame structures survive earthquakes,it does not guarantee that the structures will survive one that reaches the design capacity at a later service time.Therefore,when evaluating the seismic performance of steel frame structures in different service times,we must account for the increased seismic risks caused by steel corrosion over time.Changes in seismic performance of structures over different service times were examined in this paper. The deterioration of elastic modulus and steel yield strength were evaluated using existing empirical formulas. At the same time,the thickness variation of the column and beam cross sections in steel frame structures was accounted for by using findings from related research.Different methods including IDA,pushover,and Monte Carlo were combined together to estimate values for different limit states in a probabilistic seismic capacity model. In this paper,the maximum drift angle was taken as the damage index. The statistical parameters of the probabilistic seismic capacity model were estimated through pushover analysis,while the relationship of probabilistic seismic demand was obtained by IDA analysis for random structure samples and different service times.Seismic fragility surfaces of steel-frame structures were obtained in different limit state and different service time (0 year,15 years, 30 years,45 years,and 60 years). Finally, a case study of a 15-floor steel-frame structure was adopted to illustrate the change in structure fragility that may occur as a result of corrosion. Seismo-structure software and finite-element models were used to test different service times of the structure. Pushover and IDA analysis were then used to calculate values of different limit states in a probabilistic seismic capacity model and the relationships of probabilistic seismic demand models,respectively,over different service times. These achievements would provide theoretical support for the life-cycle design of steel frame structures,operation and management,and especially seismic hazard assessment of existing steel frame structures.

    • Characteristics of the Shear Strength of Post liquefied Silt

      2014, 36(1):7-10,15.

      Abstract (1974) HTML (0) PDF 8.52 M (1583) Comment (0) Favorites

      Abstract:Movement of the ground is the key factor in predicting structure deformation.Particularly,for prediction of liquefied ground,large deformation may destroy its superstructure even for horizontal ground.This paper presents the behavior of liquefied silt soil on the basis of lab tests.The post-liquefaction stress and strain of silt was evaluated by test results.The possibility of triggering silt liquefaction and post-liquefaction has been documented by previous studies and historical cases.The behavior of silt differed from sand in some aspects such as pore water pressure dissipation.A series of monotonic tests of liquefied silts was performed using special triaxial apparatus in which the shear strength and large deformation were evaluated for silt ground.The isotropic consolidation samples applied various effective confining pressures for different initial void ratio samples.Cyclic loading was then applied to the samples in undrained conditions. The samples were examined from initial liquefaction to the specified level of liquefaction.The undrained monotonic triaxial compression tests,known as post-liquefaction tests, were then performed on the liquefied silts. Undrained shear strength,pore water pressure,and axial strain were automatically recorded at each stage to determine the shear strength behavior post-liquefaction.In addition,large deformation was evaluated from the relationship of the stress and strain of post liquefaction.The liquefied silt behaved as dilative soil during the post-liquefaction stage.The soil resembled fluid with nearly zero effective stress.The axial strain increased up to 3% at nearly zero effective stress,after which time the pore water pressure decreased and the effective stress began to increase.The increasing axial strain was associated with nearly zero effective stress at the beginning of post-liquefaction. It is noteworthy that soil experienced perfect plastic deformation during the zero effective stress stage. Soil particles lost contact when initial liquefaction occurred during cyclic loading.The condition at the end of cyclic loading was the initial condition for the post liquefaction tests.Therefore,the soil particles with no contact showed nearly zero effective stress.The soil particles regained contact with each other with the dissipation of pore water pressure,and the soil strength also began to increase. It was demonstrated that the initial effective confining pressure and initial void ratio had a great effect on the undrained shear strength of the liquefied silts.Steady shear strength was reached as pore water pressure dissipated.A linear relationship was noted between post-liquefaction steady shear strength and initial confining pressure.The shear strength of the liquefied silt was larger than that with a smaller initial void ratio.

    • Analysis of Fatigue Damage Caused by A Series of Earthquakes at Putian, Fujian on August 2013

      2014, 36(1):11-15.

      Abstract (1322) HTML (0) PDF 9.78 M (800) Comment (0) Favorites

      Abstract:Earthquakes are among the most serious natural disasters. The causes of earthquake are very complex,with trigger factors covering many fields of science.Scientists have been attempting to develop approaches for earthquake prediction for decades,with the aims being to define processes involved in earthquakes and to minimize the losses caused by earthquake disasters.Therefore,earthquake prediction has become an active area of research.Thus far,accurate and reliable earthquake prediction is still not possible,worldwide.The fundamental reason is that we have not fully mastered the mechanism,development,and occurrence processes.Fracture of materials acted on by cycling load is called fatigue.The damage process of materials under dynamic loading is known as fatigue process.The damage process of fatigue consists of initiation of cracks and rapid expansion of the cracks.The strata bear a cycling load due to the rotation of the earth and other seasonal factors.The crack of strata often appears due to damage process of fatigue under a variety of internal and external periodic dynamic loads.The damage process also consists of initiation cracks,confluence of cracks and expansion of cracks.This paper follows the theory of fatigue damage and the calculation method of dynamic signal fatigue damage energy.Fatigue failures are one of the most common failure models when the materials are burdened by cyclic loading.Furthermore,it is well known that nearly 80% of destruction of materials is due to fatigue.A mathematic calculation model of damage energy is conducted in this paper based on system analysis theory.With the model,the damage energy during the fatigue process can be calculated rapidly using a signal.The processes of fatigue failure are evaluated by this quantitative research.The results obtained in this paper will improve our understanding of seismic fatigue.We analyzed the seismic dynamic signals recorded at Putian seismic station in Fujian on August,2013 using theory of fatigue damage.A series of earthquakes occurred in August 2013 in the Putian area,with the Putian monitoring station being about 30 km from the epicenter. Signals corresponding to a series of earthquakes were acquired by the Putian station on a time interval of one hundredth of a second.The bearing capacity of rock fatigue damage was calculated,and shows that the calculated bearing rock fatigue damage energy has the following rules:(1) the fatigue damage energy of a rock formation changes with time.(2) Fatigue damage energy is circular before the earthquake,and the cycle for fatigue damage energy is one day (24 hours).(3) the most obvious changes of fatigue damage energy occurred between 21:00 and 06:00 and between 12:00 and 15:00 Beijing time. (4) Earthquake magnitude was higher between 12:00 and 15:00,while fatigue damage energy was also higher before the earthquake.

    • Seismic Response of Subway Stations in Soft Soil Area

      2014, 36(1):16-21.

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      Abstract:With the rapid growth of urban population in recent years,traffic problems have become increasingly serious.Subways offer an effective means for solve such issues.It is worth noting that many underground structures are located in seismically active areas;therefore,seismic design and reliable assessment of underground structures must be conducted. However,many studies on earthquakes have indicated that underground structures are not as safe once believed and can collapse under dynamic loadings such as earthquake loading.Therefore,seismic design and reliable assessment of underground structures has been an important subject;however,research on seismic areas of underground structure in our country is insufficient.Particularly in areas with soft soil,where the situation is more complex,it must be resolved that the underground structures affected by seismic wave are maintained as safe and reliable.Thus,it is necessary to study the analysis theory and design method of underground structures in the soft soil areas in Tianjin by combining by including underground engineering structure characteristics and soil conditions.According to the actual engineering conditions of the typical subway station structure in Tianjin metro line 3,a model for soft soil station structures has been developed by using ANSYS software.The numerical analysis on the dynamic responses of this model under dynamic loading,Tianjin seismic wave,Taft seismic wave,and artificial seismic wave were conducted.Under different loading conditions,the internal force and deformation of main component were analyzed,particularly for of the center pillar. The displacement amplitudes of this station structure under various seismic waves are approximate and can conform to the standard requirements.The maximums of amplitudes were also determined.The internal force under the Tianjin seismic wave is the maximum,and the seismic vulnerability is located in the bottom of middle column.Therefore,these research results can be used for the seismic design of subway station structures in the soft soil area of Tianjin.

    • Pseudo static Test Research on Seismic Performance of Railway Hollow Pier

      2014, 36(1):22-27.

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      Abstract:Hollow piers are widely applied on railway bridges.In high intensity seismic regions,hollow piers and solid piers differ greatly in the arrangement of the longitudinal reinforcements and stirrups.In addition,plastic hinge mechanisms and positions of hollow piers are very different from those of solid piers.Experiments must be completed to examine solid piers on plastic hinges and then the findings applied to hollow piers.In this paper,methods of testing and numerical analysis are introduced and used to study the plastic hinge’s mechanism and position of hollow piers.Firstly,based on the hollow piers on the Dali Ruili railway,three large-scale models were made to study reasonable reinforcement arrangement,seismic damage model,and plastic hinge zone length by using pseudo-static test methods.Pseudo static test methods are the most widely used test methods for studying structural or component performances.This method maximizes the number of specimens and provides an abundance of information such as the bearing capacity,stiffness, deformation capacity,energy dissipation,and damage characteristics.From the scale model,hysteresis loop,plastic hinge zone length,and failure characteristics of hollow piers were obtained under the cyclic horizontal loads.The results show that under the design reinforcement arrangement,the model presents ductile failure whose characteristics are concrete crushing with obvious plastic hinge region.In addition,the plastic hinge zone length is similar to the dimension of the pier section (along the stress direction) at the bottom of the pier.Secondly,a fiber element model was made by using the software Opensees.During the finite element analysis,no constraint model was used for protective layer of concrete and Mander model was used for core concrete.Then,a monotonic loading skeleton curve and hysteresis loop were obtained through numerical modeling.Finally,after comparing the model results and test hysteresis curves,it was shown that numerical results were consistent with results obtained experimentally.

    • Research on Performance based Seismic Strengthening of Existing Masonry Structures

      2014, 36(1):28-33,53.

      Abstract (1398) HTML (0) PDF 11.66 M (1207) Comment (0) Favorites

      Abstract:There are many existing masonry structures in China.This structural material has low intensity and poor ductility.Substandard design,nonstandard construction,aging,and higher performance requirements mean that the safety of existing masonry structures cannot be guaranteed.The large cost of rebuilding and the huge impact on daily life and the environment make performance based seismic strengthening studies of existing masonry structures necessary.This article discusses the architectural seismic performance,seismic time history analysis,structural strengthening,and strength optimum of existing masonry structures,thus supplying reliable technical literature for practical application in engineering and revision of the related criterion.Several issues are discussed.(1) Some issues in the detection,evaluation,and strengthening of existing masonry structures are summarized,the deficits and contradictions in the detection,evaluation,and strengthening of existing masonry structures in terms of the current specifications and software for calculation are analyzed,and a homologous solution is proposed.(2) In agreement with the earthquake levels for new structures,earthquake levels for structures with a continuous seismic working life of 30 or 40 years for conditions of frequent earthquakes,anti-seismic fortification earthquake,and rare earthquakes are proposed.The factors affecting the anti seismic capability level of buildings,such as structural importance,social impact,casualties,structural damage,in house facility damage,and direct and indirect economic loss are also considered.Every factor is graded and its anti seismic capability level is quantized.The structural performance objectives are serialized,and a relation between the capability level value and the limiting value of the story drift angles is proposed.(3) On the basis of the site condition and structural condition,screen strong shock’s recorded wave and artificial fitting wave,Tianjin seismic waves,Qian’an seismic waves and artificial seismic wave can be in better agreement with the physical condition.In line with local earthquake level,adjust peak acceleration of Tianjin seismic waves,Qian'an seismic waves and artificial seismic wave in frequent earthquake,anti-seismic fortification earthquake and rare earthquake.Analyze the effective duration,and obtain proper seismic wave time histories acceleration.(4) To simplify the practical engineering and establish a finite element model,dynamic and time historical analysis is carried out for two structures using worked Tianjin seismic waves,Qian’an seismic waves and artificial seismic waves.The corresponding maximum displacements of three panel points for every layer of the structures are measured. The average value is used to reflect the displacement of each floor,and the maximum story drift angle is compared with the performance objective.The results show that the anti seismic performance requirements are not satisfied in either structure,and they should be strengthened.The results of strengthening are:(1) the location of the maximum displacement angle of a floor moves down after strengthening;(2) the reinforcement effect is clearer in the superstratum than in the substratum;(3) the presence of ring beams and constructional columns has a greater effect on the anti-seismic properties;the sectional dimensions of ring beams and constructional columns have less of an effect on the anti seismic properties;(4) the reinforcement effect is determined by the seismic waves.Different results are obtained for the same reinforcement scheme for different seismic waves:(5) the anti seismic properties will not be improved by all strengthening methods. A reasonable strengthening scheme must be selected,or the effect will be counterproductive.

    • Evaluation of Seismic Performance of a Railway Cable stayed Bridge with Multi span and Low Towers

      2014, 36(1):34-38.

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      Abstract:The structures of cable-stayed bridges are quite different from that of continuous beam bridge,so their vibration characteristics and seismic response are also different.A(64+115+115 +64)m three tower and double cable plane cable-stayed bridge was chosen as the analysis example. At pier 2# of this bridge,the tower,beam,and pier are rigidly connected together.At the other movable pier,the tower and beam are rigidly connected together,and separated with the pier.The bridge has a seismic intensity protection rating of seven.To analyze the seismic response and evaluate the seismic performance of a cable-stayed bridge,a whole bridge space dynamic calculation model was established using the MIDAS program.The spatial beam finite-element model was used to simulate the tower,pier,and beam.The cable was simulated by the tension-only spatial truss element which also took the geometrical non-linearity into account.The bearings were considered as the ideal constraint according to the actual constraint conditions.The SSI effect was also taken into account by the application of a soil spring both in the translation and rotation directions.Natural vibration characteristics were analyzed;therefore,the dynamic characteristics and vibration mode of cable-stayed bridges with multi-span and low towers were well understood.The first five vibration modes including the vibration shape and the self vibration period were extracted.The first vibration shape is an anti-symmetric vertical bending of the beam,which is similar to the continuous beam bridge.However, they differ in the vibration shape that includes the vibration of the tower and cable compared with continuous beam bridge.For low-level earthquakes,the response spectrum method was adopted to analyze the elastic response in horizontal and transverse directions.The first 300 vibration modes were used in the spectrum method,and the CQC method was used in combination with seismic response in each vibration mode.The bending-moment and shear-force diagrams of the bridge structure were drawn in horizontal and transverse directions,whereby,the results show that the longitudinal earthquake response of fixed pier 2# was the biggest and dominates the seismic design.Under low-level earthquake ground motion,the bridge is in an elastic condition,that is,the pier and tower are in an elastic state and can return to their original shape after the low-level earthquake.Under low-level earthquake ground motion,the allowable stress method was adopted in the design.The stress was calculated in accordance with the eccentric compression member and results show that the bridge can meet the required specifications to achieve performance level I.For high-level earthquake ground motion,the non-linear time-history analysis method was adopted to analyze the elastic-plastic response.The maximum plastic rotation angle should be limited within a safe range.To acquire the maximum plastic rotation angle,the artificial seismic waves under high-level earthquake conditions were input into the model,and results showed that the plastic deformation capacity can meet the required specifications and also have a degree of safety reserves.Under high level earthquake ground motion,the bridge may suffer great damage without overall collapse,which can play a role under limited traffic and after repairs;it can achieve performance level III.

    • Vibration Control Effect of Viscous Damper on Space Structure

      2014, 36(1):39-46.

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      Abstract:Supplemental damping is becoming an increasingly tested and reliable seismic design strategy,which has resulted in the evolution of building guidelines to include supplemental damped structures.The usage of supplemental viscous dampers to dissipate energy and reduce building response to dynamic inputs is gaining worldwide acceptance. The concept of supplemental dampers added to a structure is such that the dampers,rather than the structure itself,absorb much of the energy input to the structure from a transient.The placement of dampers is a critical design concern because the distribution of damping may significantly affect a building’s dynamic response and the necessary damping cost.However,current building codes and guidelines have not yet prescribed a particular method for optimal placement of dampers.Although the 2003 National Earthquake Hazards Reduction Program (NEHRP) provisions offers a methodology for determining the total damping value corresponding to a desired effective damping ratio,it does not address the optimal distribution of the dampers.This paper presents an application of viscous dampers in a space structure to suppress anticipated earthquake action.The northwestern Chinese region is an area affected by many earthquakes;therefore,seismic retrofitting of existing buildings presents many difficulties in this region. Any intervention in their structural system should neither violate their forms nor create dramatic changes in their structural behaviors.To study the vibration control of large span space structures with viscous dampers,dynamic time history analyses were performed for a gymnasium building subjected to three dimensional earthquake ground motions.To evaluate the seismic performance of the space structures,three dimensional mathematical models were prepared by using FEA ANSYS software.The models incorporated geometric (P-Δ),material (member yielding),and viscous dampers (axial force axial displacement hysteresis) nonlinearity.Seismic masses were calculated on the basis of the dead plus one second live load combination.The finite element analysis results were used to investigate the response of the building and to determine the extent of nonlinear response in members.The targets of the vibration control were to reduce horizontal displacement and member forces for the roof structure,as well as storey displacement and storey shearing force for lower frame structures.The results indicate that the seismic response reduction of the roof structure was obvious under various seismic waves,although the effect of vibration control of the lower frame structure was sensitive to earthquake frequency characteristics.The use of viscous dampers can dramatically reduce displacements and internal forces of the upper and lower structures various different seismic intensities.Uniform placement of the viscous dampers showed better vibration control performance when compared with centralized placement on the roof of the space structure.Moreover,the mode of vibration was complex for space structures,and interaction between the upper and lower structures needs to be considered in vibration reduction analysis because of its great effect on seismic response of space structures.The viscous damper system proves to be a very effective method for reducing seismic response.These research results will provide a useful reference for practical application of viscous dampers in super long span space structures.

    • Preliminary Analysis of Poisson’s Ratio of Shallow Stratum in Tianjin

      2014, 36(1):47-53.

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      Abstract:Poisson’s ratio was characterized for shallow stratum in Tianjin from more than ten borehole logs collected during the period of the“10th five-year-plan”.Associated borehole histograms and laboratory test documents were also compiled for discussion of influencing factors such as the soil moisture,wet density,and porosity ratio. Based on the borehole logging data,we developed a scatter graph of Poisson’s ratio versus depth and fit a curve to the data to represent shear wave velocity and compression wave velocity. The graph shows that the Poisson’s ratio changes by three stages as a function of depth.In the first stage,in the range of 0 to 5 m,it increases rapidly from 0.420 near the surface to 0.495 at a depth of 5 m. Fluctuation in Poisson’s ratio may result from stiff artificial soil cover of different thicknesses that formed for thousands of years of natural processes and human activities near earth surface. In the second stage,in the range of 5 to 20 m,it tends to be stable and the value mostly remains at the level of 0.495,where the stratum mainly consists of soft,saturated,and plastic mucky stratum. In the last stage,in the range of 20 to 200 m,it slowly decreases but shows considerable discreteness and some kind of linear feature is revealed by the fitting correlation coefficient.This decrease in the last stage may be the result of changes in soil lithology,soil sedimentary environment,and soil provenance at greater depths.Many cycles of transgression and regression occurred in Tianjin during the Quaternary period,so the shallow stratum mainly consists of continental facies,marine facies,and marine continental mixed facies.These varying depositional settings caused great changes of lithology,and sedimentary environment in Tianjin. Moreover,the migrations of the Yellow River and Haihe River also influenced the sediment mineral compositions greatly:In summary,the sedimentary environment and evolution mechanism strongly affected Poisson’s ratio of the shallow stratum.Factors influencing Poisson’s ratio in the sediment were examining by selecting two typical boreholes and developing a Poisson’s ratio curve and associated histogram.Additional data including curves of soil moisture,porosity ratio,and wet density were all displayed in one figure together.It shows that the Poisson’s ratio is positively correlated with soil moisture and porosity ratio and negatively correlated with soil wet density.The form of Poisson’s curve is strikingly similar with that of soil moisture and porosity ratio curves and is opposite to that of a wet density curve.By comparing soil moisture,wet density or solid mineral components,it is easy to see that soil moisture has greater effect than wet density.In other words,soil moisture is may be the key parameter influencing the soil’s Poisson ratio.Further,comparing the curve of Poisson’s ratio and related borehole histogram, we can see that the changes of soil lithology at greater depths indicate a change of Poisson’s ratio. However,it is difficult to obtain Poisson’s ratio accurately based on soil lithology because the characteristics of stratum are very complicated and strongly regional.Because of the great number of factors contributing to Poisson’s ratio,further examination of the factors is necessary especially for application in a different geologic setting.

    • Stability Evolution of Debris Landslides under Rainfall

      2014, 36(1):54-60,106.

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      Abstract:Rainfall is one external,dynamic factor that may induce landslide formation.Different rainfall intensities and rainfall durations affect the dynamic development of the seepage field,which may lead to a change in landslide stability.Research is limited regarding rainfall effects on landslide stability;therefore,a reliable basis for the deformation failure mechanism and mode analysis under heavy rainfall cannot be provided.This article examines a case study of the Shihuixi landslide in the Tongren region by applying a combination of different rainfall intensities and rainfall durations.Shihuixi landslide stability is evaluated using saturated unsaturated seepage theory and limit equilibrium theory and the SLOPE/W module.The research shows that under different rainfall intensity conditions,landslide stability deteriorated sharply after the first day of rain.Increases in rainfall intensity cause the stability coefficient to decrease rapidly,hence,significantly reducing landslide stability.When the rainfall intensity was 100 mm/d,landslide stability was basically close to whole sliding state.When rainfall duration increases,the landslide stability deteriorates sharply and the stability coefficient rapidly decreases.Landslide stability deteriorated significantly,when the rainfall duration was 2 days or 3 days.

    • Research on Dynamic Evolution of Strain Accumulation inMain Tectonic Areas of China

      2014, 36(1):61-68.

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      Abstract:Xinjiang,the northeastern margin of Qinghai-Xizang block,Sichuan-Yunnan,and North China are main tectonic and seismic regions of China. Fortunately,these regions contain dense network of GPS stations that can be used to study strain accumulation.In this paper,strain accumulations in these regions of the Chinese mainland are studied over the time periods of 2004-2007,2009-2011,and 2009-2012. We use GPS data and horizontal velocity fields that are aided by inversion of negative dislocation.Dynamic evolution features of strain accumulation at related fractures are discussed,together with abnormal status before the Lushan earthquake,and possible variation of strain accumulation after the Wenchuan and Japan great earthquakes.The results indicate that:(1) For one to several years,in North China after the Japan MS9.0 huge earthquake and the Sichuan-Yunnan area after the Wenchuan-Yushu great earthquakes,the strain accumulation rate decreased for most tectonic faults,which suggests that there is a possibility of adjustment influence after great earthquakes.It the West Qinling tectonic region in the southeastern Gansu,for a certain period after the Wenchuan earthquake,the strain accumulation rate increased,possibly showing influence of the Wenchuan great earthquake to some degree,and corresponding with the occurrence of the Minxian-Zhangxian MS6.6 earthquake in July 2013.After the Wenchuan earthquake,the southern segment of Longmenshan fault continued to accumulate strain with a slight increase in strain accumulation rate observed in 2012.This may reflect background information of strong earthquake preparation before the Lushan great earthquake to some degree.(2) Higher energy accumulation background exists at the west segment of the Southern Tianshan fracture and in the region where it meets the Northern margin fault of Western Kunlun.This same phenomenon is observed where the Anninghe fault meets the Zemuhe fault,in the middle segment of Honghe fracture,in the western segment of Qilianshan fracture,and the boundary between Shanxi,Hebei,and Neimeng.

    • Earthquake Prediction Method Based on Particle Swarm Optimization

      2014, 36(1):69-74.

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      Abstract:It is difficult to quantitatively calculate or predict earthquakes in advance;however,in areas of high density data regarding earth characteristics and monitoring prediction may be possible.This paper presents an earthquake prediction model that is based on the Particle Swarm Optimization Algorithm.The inputs of this model consist of 14 items,which are abnormal index data,they include banding,dead zone,short leveling,and so on,and the output is the classification of the earthquake magnitude.This model sets the average distance of cluster as the evaluation function of Particle Swarm Optimization Algorithm,explores and analyzes the relationships between pre earthquake precursor data and earthquake magnitude.The specific steps of the algorithm are stated as follows:Firstly,we normalize the original data of earthquake cases,which eliminates the dimensional effect;Secondly,we initialize the model parameters using reasonable values from earthquake cases;Thirdly,we pick up the speed through applying the Particle Swarm Optimization Algorithm and design the update strategy;and Finally,we design the evaluation function.If the algorithm satisfies the evaluation function,the algorithm needs to be stopped,and output the optimal solution;otherwise,it needs to turn to the third step.To verify and prove the correctness and efficiency of earthquake forecasting that is based on Particle Swarm Optimization Algorithm,an experiment in the environment of Matlab 2007a is conducted and a comparison with the classical k means Clustering Algorithm is made.The experimental data are divided into 3 categories,among which,Category 1 represents Magnitude 5~6 of earthquake,Category 2 represents Magnitude 6~7 of earthquake,and Category 3 represents Magnitude 7 and greater earthquakes.As for the accuracy rate,the overall forecast accuracy rate of k-means Algorithm is only 73.3 %;however,Particle Swarm Optimization Algorithm can increase the accuracy rate up to 83.3 %. To analyze the stability of the algorithm and the complexity of time,the results of five experiments were randomly selected to calculate the average distance among clusters and the processing time. Through analysis,we show that the processing time of the Particle Swarm Optimization Algorithm is slightly longer than the processing time for k means Algorithm.The average distance using Particle Swarm Optimization Algorithm to conduct cluster is smaller than that of k means Algorithm,this indicates that Particle Swarm Optimization Algorithm has an advantage of better stability than the classical k means Clustering Algorithm.The experimental results indicate that,this model can effectively predict the earthquake magnitude in accordance with the earthquake precursor data.Compared with the traditional cluster k means algorithm model,Particle Swarm Optimization Algorithm is much stronger,and the forecast accuracy is much higher.The research and analysis of the example of historical seismic data indicate that the model suggested in this paper makes full use of the highly robust and flexible Particle Swarm Optimization Algorithm as well as the coordination strategy of swarm intelligence.This represents a promising approach to improve the efficiency of earthquake forecast.

    • Fractal Dimension and b-value of Earthquakes in Mongolia and Its Surrounding Area

      2014, 36(1):75-79.

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      Abstract:Fractal (correlation)dimension and b-value are determined from seismic catalog recorded in Mongolia and its surrounding area.The spatial correlation of 1.56 is indicative of more or less clustered events in the region, while a b-value of 0.962 implies a highly active seismic region.A detailed study of the frequency-magnitude distribution and fractal dimension as a function of depth is also made.The results suggest structural variability at different depth levels in the Mongolia seismic zone that reflects highly heterogeneous and differential stress distribution in the region. Our result also shows that positive is the relationship between the b-value of the Gutenberg-Richter relation and the fractal dimension D of earthquakes in Mongolia region.

    • Review of the Conversional Relationship for Different Magnitude Scales

      2014, 36(1):80-87.

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      Abstract:Magnitude of an earthquake is an important measure used to compare earthquakes in space and time.There are some problems with the current magnitude scales,ML,MS,mB and mb,including uncertainty in the physical meaning and determination results are inconsistent.It is widely recognized that the moment magnitude is an absolute standard measurement of mechanics and may be an ideal magnitude scale because it is not a magnitude of saturation but stabilization.This article briefly demonstrates some progress achieved by Chinese scholars in comparing disparate magnitude scales used by the China Earthquake Networks Center (CENC) and major foreign organizations.In addition,conversional relationships between various earthquake magnitude scales are explored.We will present the comparison between the moment magnitudes for various earthquake magnitude scales and foreign standards,for example,when 6.5≤M≤7.6,mB≈MW;when 5.2≤M≤8.0,MS≈MW;when 4.2≤M≤7.0,ML≈MW;when 4.0≤M≤6.0,and mb≈MW. In each range above,the deviation between MW and mB,and between ML andMS is less than or equal to 0.2. After derivation,the comparison of moment magnitudes and earthquake magnitude scales in our regular standards are as follows:when 4.5≤M≤5.8,mB≈MW;when 4.5≤M≤7.5,mb≈MW;when 4.5≤M≤7.0,ML≈MW;And MS≈MW;MS7=MW.In the magnitude ranges above,MW deviated from mb and MS by less than or equal to 0.2,was equal to MS7;and deviated from ML by 0.22. It is suitable for all kinds of magnitude scale ranges,whereby generally:ML is applied to magnitude 1.0~5.9 earthquakes;mB is applied to magnitude 3.5~6.5 earthquakes;mB is applied to magnitude 4.5~7.5 earthquakes;MS is applied to magnitude 6.0~8.0 earthquakes; and MW is applied to all earthquake magnitudes.It is also considered a priority to catalogue conversions from the different magnitude scales.The process of earthquake rupture is complicated,between the same rupture scales (the same M0),and the altitude source spectra of some frequency are very different because of the different stress field background,rupture velocity,and rupture pattern.It is shown that there is a big difference between magnitude scales because of the limit used by different countries,different geographical conditions, instrumentation,and formula for computing magnitude.The conversion relationship between different magnitude scales is difficult to define.This article showed that the conversion formula of moment magnitude was inferred further using empirical formulas based on prior studies and not direct conversion between moment magnitude and other magnitude scales. The approach used here could be applied to earthquake forecasting.The next step to carry out the work is that establishing direct experience relation according to the thought from Mr.Chen Peisheng: establishing direct relation formula between ML,MS,mB,mb,and MW so the results may be more reliable.In addition,it would be necessary to investigate a number of parameters such as seismic moment of great earthquake,small earthquake,shallow (-focus) earthquake,and bathyseism.Seeking empirical relationships between logs M0,ML,MS, and mb is a good approach.

    • Distribution Characteristics of the Thrust Slip along Fault Depth in the Wenchuan MS8.0 Earthquake and the Interpretation Based on Numerical Simulation

      2014, 36(1):88-92.

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      Abstract:The Wenchuan MS8.0 earthquake occurred on the Longmenshan fault zone,which is a convergent zone separating the Sichuan basin from the Bayan Har block.In this paper,we analyze the latest slip model inverted from geodetic data.We find that the thrust slip distributions along the fault depth in different segments of the Wenchuan MS8.0 earthquake have common characteristics,although there are apparent complexities and differences in the Yingxiu segment,the Hongkou segment and the Beichuan segment.We decompose the thrust slip into three segments.The total amount of slip in the three segments can be decomposed into three partial slides.The first partial slide is a bottom slide distributed at a starting depth of around 17 or 18 km,with the depth range of the slide being about 2 km.The second partial slide is an intermediate slide distributed at a starting depth of around 11 km,with the depth range of the slide being about 10 km.The third slide is the remaining slide after removing the previous two partial slides from the total slip amount.The first partial slide and the second partial slide may be caused by some local rupture energy,and probably have little to do with the macroscopic mechanical environment.Thus,we take the third slide as the typical thrust slip of the three segments to compare with the other segments.After the above decompositions,the thrust-slip distributions in the Yingxiu segment,the Hongkou segment and the Beichuan segment seem to show a similar shape with the other segments.That means the thrust-slip distributions along the fault depth in the Wenchuan MS8.0 earthquake exhibit almost the same shape and follow the strike of the fault within the 200 km range from Yingxiu to Nanba,which may lead to the consistency.We construct a plane-strain numerical model using a finite-element method to examine the potential strike-slip scenarios.Our finite-element model takes the same geometry as used in the inversion of the slip model,with the exception of using a spline to imitate the seismogenic fault.Faults in the Longmenshan fault zone have steep slope at the shallow part and gentle slope at the deep part,and the dip angles of the faults gradually become smaller with depth. Therefore,a spline with two end points having fixed tangential angles is more realistic and reasonable.The southeast boundary of the model is constrained to move only up and down.Pressure is applied to the northwest boundary of the model to simulate the force exerted by the Bayan Har block on the Longmenshan fault zone.Results show that the slip distribution shapes of the fault model are closely related to the force exerted on the northwest boundary.Under the appropriate force,ruptures on the fault model would appear to have the same slip distribution shape as shown in the Wenchuan MS8.0 earthquake.Thus we conclude that the shape consistency of the thrust-slip distribution is probably due to the consistency of the shallow structures and the macroscopic mechanical environment within the 200 km range following the strike of the fault.The shallow structures of the seismogenic fault within the 200 km range are basically the same,and the force exerted by the Bayan Har block on the seismogenic fault is also essentially the same.

    • Effects of Japan MW9.0 Earthquake to the Crustal Movementof Tianjin Area

      2014, 36(1):93-97.

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      Abstract:On March 11,2011,a 9.0 magnitude earthquake occurred on the east coast of Honshu, Japan (N 38.1°,E 142.6°) and triggered a strong tsunami and serious secondary disasters including damage to a nuclear power plant. This earthquake,referred to as Japan MW9.0,was due to movement of the Pacific and adjacent plates,and also caused permanent coseismic displacement in northeast China. With the establishment of the Crustal Movement Observation Network of China (CMONOC) and China Tectonic Environment Monitoring Network(CMTEMN),we can obtain the coseismic displacement through processing and analysis of GNSS post-earthquake data.These data are useful for basic research studying seismic dynamics and characteristics,and for predicting future earthquake trends.Tianjin GNSS network has 23 GNSS stations,which belong to Tianjin Institute of Surveying and Mapping and Earthquake Administration of Tianjin Municipality.This paper examines the effect of the Japan MW9.0 earthquake on the Tianjin area.First,GNSS observation data were collected for the Tianjin area,combined with CMONOC stations and IGS stations around China,and then the crustal activity of Tianjin area after the Japan MW9.0 earthquake was calculated.The data were processed by the GAMIT software and then time series and velocity fields were obtained using QOCA software. The result was analyzed through time series,coseismic displacement,change of length of baseline and the velocity field.The results showed: that many GNSS network stations were permanently displaced a few millimeters in the east direction after the earthquake.Results indicated that the impact of the Japan MW9.0 earthquake was mainly horizontal in the Tianjin area,with no significant change in the north or vertical direction.Coseismic displacement was calculated with 3-day of time-series data from before and after the earthquake.The horizontal direction of coseismic displacement of the stations was the same,namely pointing to the direction of the epicenter;the direction of coseismic displacement in the east was about 8.5~10.1 mm.The length of baseline was also calculated with the time series,and some baselines that crossed the fault were analyzed.From the long-time trend, the entire baseline has an obvious yearly cycle.From the length of the baseline,baseline GGSL-JIXN that crosses the Cangdong fault shows some tension,while baseline WQCG-JIXN that crosses the Baodi fault shows that the baseline length increased slightly after the earthquake due to tensional stress. Results showed that the earthquake created a tensional effect on Tianjin area to some extent. The velocity field changed about 0.1~2 mm/yr in the east direction,while the velocity field in the North-South direction changed only a small amount that was within the error range.

    • Quaternary Tectonic Deformation and Geomorphologic Response Characteristics in the Southern Margin of Chengdu Basin

      2014, 36(1):98-106.

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      Abstract:Chengdu Basin is located in the front of Longmenshan Mountain,limited between the Longmenshan Mountain and Xiongpo anticline. The two major tectonic systems in the southern margin of Chengdu Basin are the Qiongxi thrust fault system and Xiongpo anticline.The Datang and the Pujiang-Xinjin are the respective major faults with Qiongxi thrust fault system and Xiongpo anticline.The landscape development of the drainages,such as Linxi River and Qingyi River,may have a feedback effect on the Late Quaternary deformation of the tectonic systems.The response relationship between tectonic deformation characteristic and landscape in the southern margin of Chengdu Basin was studied in this paper by interpreting satellite images,conducting field geological investigations,and Digital Terrain Analysis.The late quaternary tectonic deformation characteristic of Qiongxi thrust fault and Xiongpo anticline were emphatically studied in this paper.Our analysis indicates that the middle Pleistocene was an important period of tectonic deformation in the southern margin of Chengdu Basin.Through field investigation,we found that Datang fault is the west reverse fault of the Qiongxi thrust fault system and recent activity along the Datang resulted in the tectonic deformation of Ming-Qiong platform.Pujiang Xinjin fault also dislocated the Yaan gravel layer,which was formed in middle Pleistocene. So the main development and evolution of the Qiongxi thrust fault system and Xiongpo anticline were also in this stage.Because of their tectonic deformation,the ancient Qingyi River had diverted several times left a huge pluvial fan,Ming Qiong platform.Through digital geomorphologic analysis,we derived the drainage sub-basins and their hypsometric interval (HI values) in the Xiongpo area.The swath profile,crossing the southern margin of Chengdu Basin,shows that there are several fold mountains,paralleling the Longmenshan thrust belt.It is the largest terrain gradient zone in study area,and the fold structures also reflect the NW-SE oriented extension of the south segment of Longmenshan thrust belt.We extract the drainage basins from ASTER GDEM data in Xiongpo area and calculated their hypsometric interval (HI values).The characteristics of the HI values showed that there is a decreasing trend in a SW to NE orientation.The result reflects that the power of the tectonic deformation from the south is stronger to Xiongpo anticline and the deformation process of Xiongpo anticline extended from SW to NE.Our analysis illustrates that the drainage landscape has had an obvious feedback effect on the Late Quaternary tectonic deformation in the southern margin of Chengdu Basin.

    • A Preliminary Study on Seismic Tomography in Mid-eastern Segment of Tianshan Mountain

      2014, 36(1):107-113,169.

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      Abstract:The Tianshan Mountains, also known as the Snow Mountains, lie across Eurasia to border the Xinjiang Uygur Autonomous Region and Gansu province in eastern China to the western region of The Republic of Kazakhstan and Kyrgyzstan. In the west, the Tianshan Mountains split from the Ili River valley and reveal green valleys and splendid peaks. These mountains are situated between the Tarim plate and the Junggar plate and reach an altitude of 2 500 km and span 300~500 km. The mid-eastern segments of the Tianshan Mountains were selected as the study area (79°-98°E, 39°-46°N), and we utilized 35 051 natural events from 2001 to 2010 to study the crustal velocity structure. The data contains 418 915 P- and S-wave phases, which were recorded by the Xinjiang regional seismic network. We divided the research area with a mesh grid on the basis of the previous results and the character of the seismic ray distribution. Next, the finite difference tomography method and a programmer were used to invert the P- and S-wave velocity disturbance and the P- and S-wave velocity structure. Analysis of the relationship between tomography and corresponding explanations was conducted on the basis of the relationship between velocity structure and great earthquakes in history. An additional velocity model was used with several iterations of calculation to verify our results. The two models showed very close results at the same tectonic position with the same parameters. Therefore, the data and methods are credible in this paper. During the process of the iteration, the results of relocate events and ray tracing error decreased gradually with the iteration time increase. The range of error was relatively narrow after three iterating three times; thus, the third iteration calculation result was used for resolution in this paper. The resolution of image was better at a depth of 60 km, and the result was verified after testing by checkerboard in the study area.  The tomographic results suggest that the deep structures and geodynamics have significant impacts on deformations and earthquake activities in the crust in addition to the mountain building, collision, and dynamics of the entire Tianshan Mountain belt. The fluctuation of the crust velocity structure was dramatic. The low velocity area could be related to the sedimentary layer thickness and the buried depth of the basement. There are obvious high and low velocity gradient zones in the middle and the lower regions of the crust. The distributions of the high and low velocity at 60 km indicate that the dynamic contact mode of the basin and mountains conjunction is limited in the front regions of north and south Tianshan. In addition, the Moho surface depth decreased gradually from the west to the east. At the Junggar basin and Tarim basin conjunction, the Moho surface depth in the N-S direction showed obvious fluctuation. The low-velocity blocks under the basin dipped and squeezed in an opposite direction, and the depth of the Moho layer varied from 48 km to 60 km in the study area. At high and low velocity in a transition band or near the fault that includes medium variation, the region is much more likely to be the seismogenic zone and seismic zone symbol of the strong earthquake. The preliminary results show that the Tianshan Mountain uplift in crust may be related to squeezing in the N-S direction between Junggar basin and Tarim basin. 

    • Application of Robust Regression Model in Seismic Intensity Attenuation Relationship

      2014, 36(1):114-119.

      Abstract (1423) HTML (0) PDF 11.37 M (1210) Comment (0) Favorites

      Abstract:The traditional intensity attenuation relationship was analyzed using the least squares method fitting.When every observation value is assigned the same weight,outliers are unreasonably treated. Minimizing the sum of squared residuals is the objective in the error checking of the least squares regression model,and the variance is not a robust statistical unit. Therefore,this method is unstable for intensity attenuation. A stable regression for the M estimation method is proposed in this paper.The method was applied to study 117 earthquake macroscopic isoseismic lines,as well as a joint attenuation model.All selected earthquakes from 1716 to 2011 were greater than MS5.0. The results are as follows:Near the epicenter, the intensity attenuation curves in the long axis were close to those in the short axis.With an increase in epicentral distance,the decay of intensity increased along the long and short axis,and along the long shaft it was faster than that along the short shaft. In the far field,the curves of the long axis coincided with those of the short axis.Compared with historical seismic survey data,the simulated intensity of the long and short axial was consistent with the field data in the epicentral region and the far field.Under the same magnitude,the intensity of Tianshan was a slightly higher than that of Arkin and the West Kunlun Mountains in meizoseismal area,which may relate to regional site conditions.In the near field and with the same epicenter distance region, the intensity of Tianshan area was slightly higher than that of Arkin and the West Kunlun Mountains region. In the far field,in the same epicenter distance,the intensity attenuation speed in the Tianshan area was greater than that in the Altun Mountains and West Kunlun Mountains area,which was more obvious when the magnitude was greater than 7.In the far field and under the same magnitude,the attenuation curves of both shafts were similar and tended to be similar in shape to those of the Altun and West Kunlun Mountains.In the same epicenter location near the epicenter,the intensity of West Kunlun Mountains was slightly higher than that of Elgin area.In contrast,the intensity of Altun area was slightly higher than that of KunLun area in the far field position of larger magnitude.By contrast,the actual average rupture scale determined by three regression models indicated that the robust regression model was better than least squares regression and multivariate regression,and it could accurately reflect geological background and attenuation law in the Tianshan area.Therefore,it was the most fit for simulation of the actual value.In short,the robust regression model significantly improved the simulation of seismic intensity attenuation relationship for large magnitudes and has a strong practical significance for earthquake prediction in the region.Furthermore,this method provides reasonable intensity attenuation for regional seismic hazard analysis and seismic zoning.

    • Analysis of Variation Characteristics of Geoelectrical Resistivity at Changli Station before Earthquakes

      2014, 36(1):120-126.

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      Abstract:This study surveyed and analyzed the significant mutations of the original observations including observing systems of movement,the natural environment,and buildings affected facilities by examining resistivity observations at Changli station from January 1999 to May 2013. On the basis of this analysis,Changli station has used the curve tracking application and normalized variation rate method (NVRM)approach to analyze earthquakes occurring in the Chinese mainland and the surrounding region since 2000,which include the November 14,2001,West Kunlun Mountain Pass MS8.1 earthquake;the December 26,2004,Sumatra MS8.9 earthquake;the May 12,2008,Wenchuan MS8.0 earthquake;the March 11,2011,level 4 far MS9.0 earthquake in Japan;and the resistivity change of 400 km near Changli station before the earthquakes occurred. The results show a relationship among two trends and three record-breaking abnormalities and far earthquakes in addition to a relationship between these earthquakes and changes in the mechanical state of North crust in a wide range of backgrounds. According to the analysis of nine moderate earthquakes in Bohai area,five occurred within six months of abnormalities,including the abnormal frequency of EW Road between 2008 and 2009 and between 2012 and 2013 and that of NS Road in 2009.Based on the differences in intensity,seismic studies at various distances consider that the analysis of abnormal signals should be combined with the record-breaking abnormal changes,trend changes and transitions,and NVRM processing and analysis methods to analyze observations of Earth resistivity.These differences may be related to the strong earthquakes if there is a distortion or trend in abnormalities lasting 6 to 24 months. However,the level 4 and 5 earthquakes do not generally cause distortions or trend changes.

    • Comprehensive Analysis of the Distribution of Isoseismal Curve Major Axis Directions of Historical Earthquakes in Chongqing Area

      2014, 36(1):127-133.

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      Abstract:In this study,the isoseismal curve major axis directions of historical earthquakes were counted in the Chongqing area,and the dominant direction was identified.The seismic activity in this area can be roughly divided into two NE strips the route that include one along the Huayingshan fault zone and the other along the Qiyaoshan-Jinfushan fault zone.The Chongqing area is a moderate earthquake region.The historical earthquake space distribution indicates that earthquake occurred in the belt boundary fault of two or three structural units in and NE of the axis of the anticline.The NE fracture structure is dominant in Chongqing area,and the seismogenic structure of most Chongqing earthquakes is a NE-trending fault zone.Rongchang is an earthquake-prone zone in the Chongqing area,which includes seismogenic tectonic earthquakes in the Huayingshan fault zone.On the basis of focal mechanism analysis of Chongqing and adjacent areas,the potential of the seismogenic structure was examined,to provide a basis for evaluating the earthquake isoseismal curve major axis direction. Through the collection of focal mechanism solutions of moderate-strong earthquakes in this area,determination of a composite mechanism solution of small earthquakes,calculation of the focal mechanism of small and moderate earthquakes in Rongchang area,and analysis of the focal mechanism solution features,it is concluded that the tensile principal stress axes and the principal compressive stress axis are nearly horizontal in the area of the modern tectonic stress field,the principal compressive stress is.NW-SE,and the tensile principal stress is NNE-SSW.The predominant distribution of the historical earthquake isoseismal curve major axis direction is NE trending.Through the analysis of the seismic activity and active faults,it was determined that the direction of major axis orientation and active fault lines nearby show better consistency.This result indicates that despite the uncertainty in historical isoseismals for detailed records,the statistical results of long-range distribution for Chongqing,which is a moderate earthquake area,can be used to determine the local seismogenic structure and for seismic rupture location research.A section of the strike of the focal mechanism solution was consistent with the macroseismic intensity survey data obtained by the isoseismal map of long axis direction.After the earthquake,the location of the earthquake epicenter can be evaluated,and the direction of the long axis of the isoseismal can be obtained through the magnitude to develop an isoseismal model for rapid determination of the scope of the disaster.The isoseismal curve major axis direction of historical earthquakes,active faults, and the nodal plane of the focal mechanism solution in the Chongqing area are essentially consistent and can be confirmed by cross correlation.

    • Seismic Hazard and Risk Assessments in North China Based on the Historical Intensity Observations

      2014, 36(1):134-143.

      Abstract (1374) HTML (0) PDF 31.45 M (1523) Comment (0) Favorites

      Abstract:Seismic hazard and risk are two important concepts in engineering design and other policy considerations.Although seismic hazard and risk have often been used interchangeably,they are fundamentally different.Furthermore,seismic risk is more important in engineering design and other policy considerations.Seismic hazard describes the natural phenomenon or property of an earthquake,whereas seismic risk describes the probability of loss or damage that could be caused by a seismic hazard.Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space from instrumental,historical,and geological observations.Seismic risk quantification is complicated and somewhat subjective because it depends on the desired measurement of consequence(i.e.,outcome of physical interaction between the seismic hazard and exposure)and how the hazard and exposure interact in time and space.Seismic risk assessment can be expressed in many different ways for different users. A model for estimating seismic risk must make assumptions to describe how the hazard and exposure interact in time.In this paper,we first discuss the basic concepts of seismic hazard and risk,and then estimated them from 500-year intensity observations for North China.The key element of this method is to establish the frequency intensity curve that describes the relationship between intensity and annual frequency (or return period)at a site.The main content and steps are described as follows.First,historical intensity observations were collected,the earthquake catalog was checked for completeness,and aftershocks were deleted.Second,the intensity database was geo-referenced in geographic information system (GIS).Third,based on the characteristic of seismicity,the coverage,geological characteristic and population density,the region was divided into cells in which the intensity observations were digitized in GIS.Fourth,analyses were performed on the digitized intensity records to estimate seismic hazard such as the frequency (or return period)-intensity relationship for each cell.Under the assumption that the occurrences of earthquakes follow Poisson distribution,we also estimate seismic risk in terms of the exceedance probability of intensity I ≥ Ⅶ,Ⅷ,Ⅸ in 50 years,and the corresponding intensity with 10 percent probability of exceedance in 50 years.The results show that North China has high seismic hazard and seismic risk.The results also show that the current design peak ground acceleration (PGA) for many cities in North China,particularly Beijing,Tianjin,and Tangshan,might not be adequate.

    • Ten New Added Moderate strong Historical Earthquakes Occured in Ming Dynasty in Gansu,Shaanxi and Ningxia Provinces

      2014, 36(1):144-152.

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      Abstract:The provinces of Gansu,Ningxia and Shaanxi are within the region where the Chinese nation originated.Earthquakes frequently occur in these provinces,but most of the region is vast,sparsely populated and far away from the state or county government centers of China.Local earthquake events in the region were not likely to be recorded completely in historical materials,especially if the epicenter was far from cities where it could be felt and reported.Therefore,historical data are likely to be limited and a large number of earthquakes may have been omitted from the records.Historic earthquakes,having their epicenter in the remote regions,may have been felt in cities but because of the distance between epicenter and detection it is difficult to objectively and quantitatively evaluate this historic earthquake activity.Further research on this part of historical data,aimed at more scientifically determining the basic parameters of the omitted moderate-strong historical earthquakes can contribute to a greater understanding of earthquake activity in this area. Improved objective analysis will help to define the social and economic benefits of safety evaluation for major engineering projects or disaster defense.In the study of historical earthquake data and field investigation in Gansu,Ningxia and Shaanxi provinces,we collected data related to ten moderate-strong historical earthquakes.We derived the basic parameters of each earthquake by comprehensive analysis,comparison,and statistical computing for the felt earthquakes.Seismic-tectonic activity in this region was then analyzed using the basic parameters.The strength of earthquakes was calculated using the following formulas:The relation between radius of equivalent circle of IV degree in western China and magnitude given by the Department of Seismic Hazard Prevention of State Seismological Bureau in 1995, is M=1.68lgR+2.24 (1) Where R is the radius of equivalent circle in kilometers and M is magnitude. In addition,another empirical formula given by Jiang Mei et al. (1997),is M=3.04lgRi-0.82 (2) Where Ri is the long radius of feeling area in Gansu,Ningxia and Qinghai provinces in kilometers and M is magnitude.In this study, the estimated magnitude is the average value of applying these two empirical formulas,which allows us to properly consider the local human environment and geographical conditions. The relation between magnitude M and intensity Ⅰ0 in Western China is M=0.605Ⅰ0+1.376 (3) Using this statistical formula,we calculated the intensities of each historical earthquake.The parameters of moderate-strong earthquakes in the Gansu,Ningxia and Shaanxi provinces for which no damage records are available could have important implications for understanding historic patterns and frequency of earthquakes in the region.Through detailed textual research that combines archaeology,science of historical materials,and geology we can develop the record of strong earthquakes that were previously omitted from the catalog for remote areas of northwest China.This can provide scientific and reliable data for seismological research and security of major constructions.

    • Influence of Seismic Fortification Criterions on the Cost of Rural Residential Projects of Brick concrete Structure

      2014, 36(1):153-157.

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      Abstract:China has suffered from many destructive earthquakes in its history.Most of these earthquakes occurred in rural areas and caused huge casualties and economic losses.If we can improve the seismic performance of the rural residential project,it will alleviate the danger of earthquake disaster in rural areas,protect people’s life and property,as well as promote the harmonious development of social and economic resources.However,due to the unpredictability of earthquakes and the limitations of human resources,it is difficult to determine reasonable investments for rural housing structures.This study will calculate the rural construction cost in different seismic fortification criterion and provide a scientific basis for earthquake disaster mitigation.This paper chooses a brick-concrete structure as representative of the rural residential project and the research objective of China’s rural areas.The cost of constructing the brick-concrete structure is calculated under different seismic fortification criteria.The results are that unilateral cost is increased by about 17% in seismic intensity of 6 degrees relative to the undefended cases,and by about 11% for seismic intensity of 6 to 7 degrees, or by about 17% from seismic intensity of 7 to 8 degrees.Through analysis and comparison,we found that differences in rural construction costs of a brick-concrete structure were mostly related to the cost of raw materials.Materials for a brick-concrete structure rural residence increased by about 65%,with the cost of rebar and concrete increasing the most.Our work suggests that it is difficult for the current farmers to independently raise funds for the rural residential project of brick-concrete structures.Our government must provide adequate financial support to assist the rural residents to increase fortification standards for the structures.

    • Study on Tectonic Stress Field in Yishu Fault Zone and Its Adjacent Areas

      2014, 36(1):158-169.

      Abstract (1113) HTML (0) PDF 19.40 M (1159) Comment (0) Favorites

      Abstract:Yishu fault zone is the most famous fault zone in eastern China. According to the historical earthquake catalog,the MS8.5 Tancheng earthquake occurred in 1668 along one of the zone's faults known as Changyi-Dadian Fault.Because this fault zone is important in the research of geologic history in addition to that of potential earthquake risk,it is well known by geologists and seismologists. Numerous research papers have focused on the tectonic stress field evolution and characteristics of modern tectonic stress fields in the region near Yishu Fault.Regarding the evolution of the tectonic stress field in the region near Yishu Fault, such research has always included information on geodynamics,tectonic deformation,and structural geometry.However,such research is used to determine the characteristics of tectonic stress fields in multiple periods and is generally based on simulation tests and numerical simulation.All of this research is aimed to reveal the tectonic structural framework as well as tectonic evolution to provide an understanding of the inherited and newly created features of tectonics and,in particular,to provide a basis for study of modern tectonic stress fields. In the region near Yishu Fault,modern tectonic stress field studies have generally focused on crustal movement,focal mechanism solutions,borehole strain measurements,and numerical simulation.Because such research also focuses on the characteristics of spatial distribution and the changes of modern tectonic stress fields,it serves as references for analysis of seismic hazard in this region.In this paper,by analyzing numerous studies,we systematically summarize the characteristics of tectonic stress field evolution for the region near Yishu fault zone.Although there are many different theories on the generation of the Tan-Lu fault zone its active features,we conclude that Yishu fault zone originated through large scale left translation in the early years and the later experienced complex tectonic evolution. Finally, determine that the direction of principal stress axes of the ancient tectonic stress field changed significantly along with the active behavior of this fault zone to reach 100 MPa. With developments in technology,current studies of tectonic stress fields are more encouraging,and many new research methods and novel concepts have been explored. In particular, the development of digital computer simulation techniques has allowed for an increasing number of studies in this research field,such as the progression of stress field numerical simulation from two dimensional to three dimensional and research perspectives from single to multiple levels. On the basis of previous research in the region of Yishu Fault, we conclude that the direction of principal stress axes was consistent with NEE and that principal stress values were increasing with depth from 3 MPa near the Earth’s surface to 100 MPa to approximately at 10 km. These parameters are characterized by complexity regardless of the direction of principal axis or tectonic stress values,particularly near Earth’s surface.Thus,research on the tectonic stress field in the region near Yishu Fault is thorough. Although some of these theories are divers,many viewpoints are still highly significant and provide a basis for further research in estimating potential earthquake risk in this fault zone.

    • Discussion on the Prediction Methods for Reservoir induced Seismicity

      2014, 36(1):170-177.

      Abstract (1265) HTML (0) PDF 14.29 M (1334) Comment (0) Favorites

      Abstract:Earthquakes can be triggered by water storage and drainage,near reservoirs,and may be referred to as Reservoir Induced Seismicity(RIS).One area of research is to predict the possibility,location,probable maximum of induced earthquake,and earthquake development trend according to the seismic activities after impoundment.Usually the intensity of reservoir-induced earthquakes is small,but reservoir-induced earthquakes may play a role in triggering shallow-focus earthquakes that have a greater effect on the dam.RIS may also induce large earthquakes,such as the Xinfengjiang reservoir earthquake.Therefore,scientific forecasting and corresponding precautionary measures are the premise and basis of earthquake disaster preparedness and mitigation.The existing prediction methods were classified as three categories in this paper according to their characteristics,including qualitative forecasting,quantitative prediction,and monitoring and forecasting.The qualitative forecasting method is mainly based on the understanding of the mechanism of reservoir-induced earthquakes,and various predictions can result from different analytical processes.The quantitative prediction is used to predict the possibility and probable maximum of induced earthquakes,and combines empirical knowledge of reservoir earthquakes with mathematical theory.The monitoring and forecasting method is mainly based on monitoring data,and the object of study is an existing reservoir.Each of the prediction may use a variety of methods including earthquake up-limitation magnitude,empirical analogy method,high magnitude b-value and low magnitude b-value ratio prediction method,load-unload response ratio theory,probability prediction,fuzzy comprehensive evaluation,and comprehensive impact parameter.In this study,advantages,existing problems,and directions of development were investigated for these methods.The results show that the current forecasting methods are inefficient for evaluating RIS due to a lack of understanding of the mechanism,the complex multiplicity of problems and the data limitations of earthquake cases. Research on mechanisms for reservoir induced earthquakes should be strengthened to improve ability to predict RIS.In practical application,the likelihood and possible magnitude of RIS should be determined by a combination of several methods and considering site specific conditions.Predictive methods should be based on the seismic,specific hydrological and geological environment data of the local and reservoir area.Predictive methods that are based on monitoring data are likely to be the main direction of research on the topic of RIS.

    • Execution Auxiliary System for Earthquake Contingency Plans

      2014, 36(1):178-185.

      Abstract (1150) HTML (0) PDF 17.09 M (1140) Comment (0) Favorites

      Abstract:Earthquake contingency plans provide guidance for earthquake emergency response and play an important and practical role in earthquake emergency and rescue. However,earthquake contingency plans may have some shortcomings such as being difficult to display,inconvenient to search,and incapability of automatically correlating targeted disposal solution with the development and variety of earthquake disaster.The main reason for these shortcomings and challenges is because most earthquake contingency plans are in a non-digital text (i.e.,hard copy)form.Digitalization makes the formulation and implementation of an earthquake contingency plan more practical and allows for rapid visualization and computer-based interactive use.According to earthquake disaster disposal flow and real-time information,targeted and comprehensive disposal solutions can be formed.Execution auxiliary systems are a type of digitized earthquake contingency plan.When implemented in a platform that includes an execution auxiliary system,an earthquake contingency plan can play an important role in emergency information sharing and command decision-making.The construction of an execution auxiliary system for an earthquake emergency plan will significantly improve the capacity of earthquake emergency response and make for highly effective emergency disposal.The key technique of the system construction is the method of digitizing an earthquake contingency plan so that it can be integrated with related emergency technology systems.The digitization of an earthquake contingency plan means to transform the text and natural language that describes earthquake contingency plans into structured and logical forms that can be recognized and processed by a computer.In this process,earthquake contingency plans are transformed from static storage formats into digital storage formats.The digitization process for earthquake contingency plans mainly includes formal description and digital modeling,which are explained in this paper.The execution auxiliary system mainly includes the system business processes,the general design,the function design,the database construction and the interface design.This paper emphasizes the external interface design,which will allow for information sharing with related systems such as Earthquake Instant Messenger (EQIM) system and earthquake emergency command technology system. The execution auxiliary system implementation is GIS based and consists of five functional modules, including emergency management,preplan management,normal management,templates management,and system management.This paper mainly described the function of the emergency management module and demonstrated the application of the emergency management module using an example simulated earthquake. Further research will combine reasoning techniques in the AI Application with a practical application background. Adaptive adjustment of earthquake contingency plans will be made automatically according to specified rules defined within the system,combined with knowledge and experience of decision-makers and experts in this field.Thus,the reliability and availability of an execution auxiliary system for earthquake contingency plans will be greatly improved.

    • Database Construction of Shallow Seismic Exploration for Active Fault Detection in Urban Areas: A Case Study of Shizuishan

      2014, 36(1):186-194.

      Abstract (1205) HTML (0) PDF 15.87 M (1099) Comment (0) Favorites

      Abstract:A large number of seismic studies in urban regions show that buried active faults are the culprits for many urban earthquake disasters. Identification of buried active faults is important for managing seismic risk associated with new development in our city.Shallow seismic exploration techniques can reveal concealed fault features,deep distribution status,and nature of activities and other information; therefore,it is an important technique to locate active faults in an urban active fault survey project.A shallow seismic exploration records the position of survey points,distribution of survey lines,location of breakpoints and other details;therefore,it provides important physical data that can be used to explain geological fault models for the urban active fault study.This paper introduces the application of the shallow seismic exploration technique to the city of Shizuishan,and discusses the construction of a shallow seismic exploration database model. It details the technique,processing,and approach for building the database using 33 shallow seismic exploration lines crossing four buried active faults in Shizuishan. The objective of building a shallow seismic exploration database is to reorganize a lot of information provided by the geophysical department,and turn them into binary data based on an ArcGIS system.The construction of the database includes four steps of organizing information (referred to as archive data) including filling attribute data,creating geometry features,importing attribute data,and importing archive data into the database. Archive data are stored in a specific storage space so that users must access them with specific software.The attribute data are filled in using an Excel formatted table and imported in a later step.The geometry features were created and imported into the database using ArcMap.Finally,bulk storage software was used to import attribute data and archive data into the database.This method was practical,quick,and accurate because it simplified database construction and increased work efficiency.The construction of a shallow seismic exploration database should be synchronized with field work. In addition,at the end of database construction,the primitive data map and fault distribution map should be updated and stored in the completed shallow seismic exploration database.The database is delivered to and tested by the center for management,where data can be concurrently shared for surveying and prospecting of active faults and corrected based on the test reports.

    • An Investigation of Information Publication the Key Area of Earthquake Monitoring and Protection

      2014, 36(1):195-200.

      Abstract (1390) HTML (0) PDF 10.83 M (1129) Comment (0) Favorites

      Abstract:The staff of earthquake prevention and mitigation in the city and county undertakes the important responsibilities of implementing the system, objectives and tasks of the key area of earthquake monitoring and protection (hereinafter referred to as the earthquake key area). Their awareness of information publication of the earthquake key area is directly related to the work of seismic prevention and mitigation. Taking the earthquake prevention and mitigation staff as object, the paper starts with the importance of information publication of the key area of earthquake monitoring and protection. The questionnaire contains several aspects (such as agreement or disagreement, ways of publication, objects of publication and so on), which provides the basis for making the information of the earthquake key area known to the public. Through the analysis of survey data, we draw the following conclusions and recommendations: the information in the earthquake key area should be opened, and the lists of cities and counties in the earthquake key area must be known to the public. At the same time, we should intensify the publicity of knowledge related to the earthquake key area.

    • Mechanism of Gravity Anomaly before Earthquake and Its Role in Earthquake Prediction

      2014, 36(1):201-206.

      Abstract (2723) HTML (0) PDF 10.15 M (9531) Comment (0) Favorites

      Abstract:Earthquakes are among the major natural disasters facing the world.Earthquakes can threaten safety of people and cause serious damage to property and the economy of a region.Our country is one nation that has had serious earthquake disasters throughout history,with 4 400 large earthquakes being recorded.Seismic intensity is 7 degrees or higher for 60 % of the nation’s land,with 50% of the cities and 67% of the big cities located in these high(i.e.,≥ 7) intensity areas.Therefore,having the ability to predict earthquakes would help to reduce the risk posed to people and human made structures.This article examines the gravity anomaly,one of the earthquake forerunners,and the relation between gravity anomalies and earthquakes.This study is based on the concept that when tectonic movement occurs,the earth’s crust extrudes or extends in every direction. As a result,gravity will be in a state of imbalance and under the action of an equilibrium force,the earth’s crust will restore to a balanced stable condition.During this adjustment,the gravity field will adjust and change until balance is restored.A formula is used to briefly describe the three influencing factors that affected the gravity anomaly:the density changes,movement of the outer fluid,and changes of measurement elevation.In the second part of the study,gravity variation diagrams are drawn with respect to time and space before the earthquake of Yushu,Tangshan and Wenchuan.It can be seen from the cases that the gravity anomaly before earthquakes is obvious:gravity changes constantly near the epicenter,and the gravity gradient is higher than usual.There are strong tectonic activities during earthquake gestation.Large deformations are produced in the fault zones and the weak areas of the earth’s crust,thus forming some crustal thickness difference and density difference,and the phenomena of gravity anomalies are shown.In this part,the causes of the gravity anomaly are also conjectured:tectonic movement and the invasion of subsurface fluid. Finally,two prediction methods of gravity are introduced:mobile gravity observation and GRACE gravity observation.The gravity changes because of crustal deformation and material changes in the fault zones,which result from crustal movement during earthquake gestation.We believe that evolution characteristics of the gravitational field can help us to explain current tectonic activity.The whole process from gestation to eruption of the mid-strong earthquake can be tied to gravity anomaly,thus providing reliable basis for earthquake prediction.Through the study of the gravity anomaly,the characteristics and change can be understood including the quality and density of underground medium,change of elastic modulus of the crust,and relationships between gravity anomalies and earthquakes.The related indicators of the short to medium term earthquake prediction in mobile gravity observation are summarized,and the case of Wenchuan earthquake is used to summarize the method of long term earthquake prediction using the GRACE satellite observation.

    • A Pseudo dynamic Relationship for Describing the Cyclic Stress strainResponse of Soft Clays in Undrained Conditions

      2014, 36(1):421-428.

      Abstract (798) HTML (0) PDF 263.52 K (1062) Comment (0) Favorites

      Abstract:In this study,we develop a pseudo-dynamic relationship describing undrained cyclic stress-strain responses of soft clay elements under general stress conditions,based on equivalent visco-elastic and creep theories.This relationship includes three basic parameters:the cyclic shear modulus,the damp ratio and the cyclic accumulative strain increment.The variation of the cyclic shear modulus and the damp ratio with the octahedral shear strain are used to describe undrained cyclic strain.The cyclic accumulative strain increment is determined based on the Mises creep potential and the associated flow rule.We determine these by unconsolidated and undrained cyclic triaxial compression tests of soft soils.We made cyclic triaxial extension and torsion test predictions using the parameters determined.Predicted variations of the cyclic shear modulus and the damping ratio with the octahedral shear strain are basically in agreement with the test results from the cyclic triaxial extension tests.Predicted variations of the cyclic accumulative strain with respect to the number of cycles is also basically in agreement with the test results for the cyclic torsion tests wherein the static and cyclic deviatoric stresses have the same direction.The predicted variations of the cyclic accumulative strain are less than those of the test results when the direction of the static deviatoric stress is different from the direction of the cyclic deviatoric stress in the cyclic torsion tests.

    • Vibration Test and Analysis at the People’s Square of Shanghai,Metro Line 1

      2014, 36(1):429-433.

      Abstract (1206) HTML (0) PDF 347.08 K (1227) Comment (0) Favorites

      Abstract:A field test was performed in the subway tunnel of metro Line 1 at Shanghai People’s Square Station. According to the data of the track acceleration test and the equation of the vehicle system vibration,a simulated deterministic expression of the metro load was obtained.The ground vibration due to the moving metro was simulated by applying the load to an FLAC3D numerical model. Through comparison of the numerical analysis results of different working conditions, the wave propagation, and attenuation at the ground surface, the dependence of the ground vibration on the tunnel depth and the frequency of the simple harmonic excitation load are analyzed.

    • A Nonlinear Seismic Response Analysis Model for UndergroundTunnels Based on the Viscous spring Boundary

      2014, 36(1):434-440.

      Abstract (728) HTML (0) PDF 371.99 K (1084) Comment (0) Favorites

      Abstract:This paper presents a model for the nonlinear seismic response analysis of tunnels,in which the viscous-spring boundary method and the earthquake equivalent node force input method are combined for half-space seismic excitation and the general finite element software ANSYS is utilized for analysis.The model uses the equivalent linear method to model soil nonlinearity and combines Rayleigh damping and material damping to model soil damping.Concrete and reinforcement nonlinearity are considered separately,and soil-liner contact is taken into account. The model is validated through comparisons with the results in the existing literature.The nonlinear seismic response of the metro twin tunnels in Tianjin City with thick soil layers is implemented,and it is shown that when two tunnels are close, the tunnel tunnel interaction is significant and nonlinear seismic stresses of the two tunnels become larger.This model can be used for the nonlinear seismic analysis of underground structures.

    • Effects of Soft and Hard Interlayers on Ground Motion Characteristics

      2014, 36(1):441-445.

      Abstract (1117) HTML (0) PDF 318.82 K (1034) Comment (0) Favorites

      Abstract:The program for one-dimensional equivalent linear soil seismic response is verified using the underground and surface seismic records of the KiK network in Japan.The results show that,in the range of small soil deformations,the calculated ground motions are consistent with the actual motions for the sites where the stiffness of soil layers increase with depth,but not for the sites with soft or hard interlayers.Accordingly,this paper presents a method to study the effects of soft and hard interlayers on ground motions.As a reference,the interlayer is replaced by a normal soil layer to meet the condition of increasing stiffness.Then,the surface seismic response excited by the actual underground motions is computed using the program.Comparing the computed motions and the actual motions on the surface,conclusions can be drawn.Some representative sites are studied in this paper.The results show that the effects of soft and hard interlayers on ground motions are consistent;there is an amplification of high-frequency motions if the interlayer is shallow,but there is an action of seismic isolation to high-frequency motions if the interlayer is deep.

    • D-S Theory-Based Parameter Estimation and its Application in Loess Landslides

      2014, 36(1):446-451.

      Abstract (916) HTML (0) PDF 362.52 K (1122) Comment (0) Favorites

      Abstract:Parameters of rock and soil materials are the key factors in the calculation of landslide stability,but these parameters necessarily exist with some uncertainty.This reduces the reliability of stability evaluations and has an important influence on engineering safety,engineering design optimization,and other aspects of engineering.The Dempster-Shafer (D-S) evidence theory is the most efficient method of solving the uncertainty of multiple parameters.It is a kind of expansion of probability theory that is able to not only distinguish between uncertainty and what is unknown but also deal with the uncertainty caused by unknowns.The D-S theory can provide consistent results by means of combining independent pieces of evidence and dealing with synthesis problems of fuzzy and uncertain information.It has been adapted to and achieved sound results for problems in artificial intelligence,system decision-making,diagnoses,assessment,and other practical problems in various fields.In this study,the D-S evidence theory was introduced to select and estimate slip soil mechanics parameters.The parameter selection and the revised counter-calculation of the selected parameters of a typical loess-red layer interface landslide in the Gansu province were conducted on the basis of the D-S combination rule.First,combined with the huge actual mechanical parameters of slip soil of the loess landslide by tests,the D-S evidence theory was adopted to D-S evidence analysis of huge mechanical parameters of slip soil of the loess landslide.Thus,the discernment frame and basic probability assignments of the mechanical parameters of slip soil were established from the subjective and objective aspects.Secondly, the D-S combination rule was applied to combine the reliability of multiple test parameters to achieve the optimal mechanical parameters of sliding zone reliability estimates.Finally,a revised counter-calculation of the slip soil mechanics parameters was applied for the demonstration of the obtained parameters.The results show that the D-S evidence theory is an effective approach to estimate and select the slip soil mechanics parameters.The parameters obtained from the D-S evidence theory coincide with the revised counter-calculation analysis of the slip soil mechanics parameters;such results show that the theory is applicable to dealing with the uncertainty of the above parameters.Furthermore,the slip soil mechanics parameters obtained from the D-S evidence theory can help to better reflect the actual conditions of the landslide,providing a reliable basis for the stability evaluation of loess landslides.In addition,the mechanical parameter estimation of loses landslides based on D-S theory are valid and reliable;moreover,it plays an important role in geotechnical engineering laboratory test data processing and stability calculation of mechanical parameter selections and is significant in the stability evaluation of the loess landslide.

    • Consolidation of the Softening of Soft Soil under Wave Loading

      2014, 36(1):452-456.

      Abstract (695) HTML (0) PDF 447.40 K (1214) Comment (0) Favorites

      Abstract:A breakwater was constructed near Shanghai Port,China,in order to deepen the navigation channel along the Yangtze Estuary.In some sections of the breakwater a thick layer of soft soils was installed prior to construction.The breakwaters,designed as gravity-retaining structures,are made of prefabricated,semicircular concrete caissons.During construction,the caissons in one section failed during a heavy storm.In this study,the causes of the failure were investigated by running dynamic triaxial tests on undisturbed soil samples taken from the construction site.We found that the dike failure was induced by the weakening of the soft soil layer below the foundation.This paper describes the design of a guide dike and related soil improvement projects.We adopted surcharge preloading and prefabricated vertical drains to improve the soft soils below the caissons.These soil improvement measures were proven to be effective in maintaining the stability of the breakwater in subsequent heavy storms.

    • Calculation of Soil Pressure Considering the Softeningof Soft Soil during Earthquakes

      2014, 36(1):457-461.

      Abstract (876) HTML (0) PDF 245.22 K (1145) Comment (0) Favorites

      Abstract:To calculate the soil pressure of a retaining wall during earthquakes,previous methods have added only the dynamic load applied to the retaining wall or made an appropriate reduction in the internal friction angle of the soil,before calculations based on the pressure at rest.This paper,through experimental study,determines the dynamic triaxial strength variation of soft soil under dynamic loading,and then provides a method for determining the strength of the softened soil.We develop a method for calculating soil pressure that considers the softening of soft soil during an earthquake.We compare the soil pressure results in example cases that consider the softening effect with those that do not consider the softening effect.Our research results provide a strong basis for calculating the influence of soil pressure under earthquake loads and other dynamic loads.

    • Influence of Pile Sinking on Pile Capacity during Pile Driving on Offshore Platforms

      2014, 36(1):462-467.

      Abstract (971) HTML (0) PDF 456.87 K (1082) Comment (0) Favorites

      Abstract:Pile sinking during pile driving is common.A sudden drop of a pile after a strike from the hammer may cause a serious accident,such as the pile falling out of the drive cap or damage to the pile from high tension stress.Pile sinking also often causes a large deviation between the drivability prediction and the measured blow count.Therefore, an accurate assessment of pile capacity after pile sinking becomes an important problem to address in practice.In this paper,two projects in the East China Sea are chosen to analyze.Based on the results of dynamic load tests in the field and pile driving records,the influence of pile sinking on pile capacity at the end of driving (EOD)is studied.The analysis results show that pile sinking will lead to a significant decrease in the total energy used in pile driving.The results from CAPWAP show that the unit friction of a soil layer where piles run off is close to zero,while the pile end resistance shows no obvious abnormalities.This indicates that the decrease in pile capacity caused by pile sinking is mainly from friction reduction.In this instance,the pile capacity reduction resulting from pile sinking can reach a maximum of 17% of the designed value.

    • Experimental Study of Horizontal Dynamic Response andP-Y Curves of Piles during Earthquakes

      2014, 36(1):468-475.

      Abstract (967) HTML (0) PDF 467.14 K (1045) Comment (0) Favorites

      Abstract:The horizontal dynamic response of pile foundations in liquefiable soil has always been an important research question in the geotechnical field and the field of earthquake engineering.Based on the shaking table test with different input waveforms,the horizontal dynamic interaction responses of the soil-pile-slab system and the variation of the P-Y curve were analyzed using the FBG system.The P-Y curves of each pile in the pile group and single piles were compared with the API specification method.The research results showed that magnification of cap acceleration and displacement was small in general for non-liquefied tests.The cap acceleration and displacement of single piles were 2 to 3 times greater than for piles in the pile group,while the cap acceleration and displacement of piles in the pile group were 2 to 3 times greater than for non-liquefied cases.The slope of the P-Y curve for non-liquefied tests agreed well with the API specification method; however,the P-Y curves for both single piles and piles in the group were needed to reduce the API method appropriately in saturated soil.

    • Comparison of Measures for Eliminating High-frequency Instability of a Multi-transmitting Boundary in Scattering Problems

      2014, 36(1):476-481.

      Abstract (727) HTML (0) PDF 423.89 K (1052) Comment (0) Favorites

      Abstract:The multi-transmitting boundary is a local artificial boundary widely used in the numerical simulation of near-field wave motions in infinite media. But,like other artificial boundaries,the multi-transmitting boundary is unstable in numerical simulations.In this paper,we analyze the cause of this high-frequency instability and discuss the applicability of previous stability measures by performing numerical scattering problem experiments.We found that(1)for the perfect elasticity problem,the filtering method is more suitable for eliminating high-frequency instability,but it must be used carefully because of the need to consider the empirical value of the parameters;and (2)for the viscoelastic problem,the explicit difference scheme with a suitable damping value is more suitable for eliminating high-frequency instability due to the energy dissipation of the difference scheme.This scheme is also more convenient for application because no empirical parameters must be considered.

    • Seismic Stability Analysis of Highway Subgrade Based on the Pseudo-static Method

      2014, 36(1):482-488.

      Abstract (781) HTML (0) PDF 286.99 K (1384) Comment (0) Favorites

      Abstract:China is an earthquake-prone country,especially in its central and western regions.Earthquake is an unexpected event,and while its occurrence is not frequent,it can be catastrophic,and its effect on high grade highways is no exception.Previous research has rarely addressed the dynamic characteristics of subgrade filing and the stability of subgrade structures under earthquake loads.The effect on the seismic dynamic load,as documented by the current“Code for the Design of Highway Engineering,” typically uses the region of earthquake intensity as its only reference.This code does not consider seismic vibration frequency,the duration of an earthquake,or other characteristics.Therefore it cannot accurately reflect the characteristics of a subgrade structure during an earthquake. In this paper,we carry out research on the dynamic stability of the roadbed structure using the pseudo-static method.We have improved upon the quasi-static method with respect to its formula for the dynamic stability of the roadbed structure.The retaining wall acceleration,as affected by the seismic load,is considered in the calculation of the earth pressure on the retaining wall,as is the influence of the seismic acceleration distribution coefficient.With respect to the roadbed,we also improved the seismic inertia force by introducing the acceleration distribution coefficient.From these pseudo-static method modifications,the stability calculation formula for subgrade slopes was thereby improved.

    • Study on Difference of Ground Motions in Faulted Basin of Xichang

      2014, 36(1):489-494.

      Abstract (738) HTML (0) PDF 490.70 K (1206) Comment (0) Favorites

      Abstract:In this study, by analyzing the peak ground acceleration (PGA) and spectral characteristics of the earthquake acceleration records from the main shock of the Wenchuan earthquake, the difference of the ground motion at both sides of the Anninghe fault zone is discussed. By analyzing the local site conditions at the observation stations, such as local site soil, topography, and tectonics, a preliminary explanation of the discrepancy is obtained, and the numerical solution of 2D model of this site derived by the explicit finite element combined with the local multi transmitting artificial boundary method is used to interpret the mechanism causing the difference in the ground motion. The results of numerical calculations indicate that in spite of its simplicity, such an idealized model is also successful in reproducing many of the essential characteristics of ground motion and the mechanism causing the difference in ground motion within the fault zones of Anninghe. The characteristics of the faulted basin under control of the Anninghe fault zone may be used to interpret observed seismic data obtained during the Wenchuan main shock and theoretical calculations of nearby fault responses in Xichang.

    • Buckling Restraint Conditions for Innovative Aluminum Alloy Energy Dissipation Braces

      2014, 36(1):495-503.

      Abstract (819) HTML (0) PDF 265.66 K (1078) Comment (0) Favorites

      Abstract:The concept of structural damage control,introduced in the seismic retrofitting area in the late 1980s,has become popular in its applications for engineering bridges and buildings.Under strong or severe earthquake excitations,plans are made such that damage is expected to take place in energy dissipation devices and the primary structure can be kept away from the damage.Among many types of damping devices,increasing attention is being paid to hysteretic dampers,because the inelastic deformation capacity of metallic substances presents an effective approach in transferring seismic energy to other forms of energy at a low cost.Buckling-restrained braces (BRBs),as an axial-type hysteretic damper,are widely studied through their component behavior and system applications in civil engineering.Aluminum has drawn our attention for improving the durability of high-performance BRBs.Usually,aluminum and its alloys need no protection against atmospheric or chemical corrosive agents,because aluminum oxide,which is naturally generated on the surface of the metal,protects the body of the metal against corrosion.Because of the advantages of aluminum and its alloys,such as its light weight,corrosion resistance,ease of production,and economic and environmental benefits,aluminum alloy is selected for the manufacture of BRBs in this paper.Further numerical analysis of the mechanical behaviors of the aluminum alloy BRB (ALBRBs) was conducted based on aluminum alloy material tests and corresponding BRB tests,which were performed abroad.The objective of the analysis is to conduct a parametric study of BRBs with different gap widths(between the core and the restraining member)and initial imperfections to investigate the buckling behavior of the brace.The core plate and BRM were modeled using 8-node C3D8R linear brick elements with reduced integration.Large displacement static cyclic analysis was performed using the ABAQUS 6.10 general purpose finite element program.The results showed the conventional BRB design method does not consider the effect of initial imperfections and eccentricities,but the safety factor method can solve this problem.In order to enhance the aseismic ability of space structures,a new type of ALBRB was developed.The characteristics of the new ALBRB showed more reliable performance and simple construction,as well as decreased mass.Analysis of the buckling restraint conditions of the new ALBRB was completed.Results show that the stability of the ALBRB was good under monotonic loading and that it completed the full hysteresis loop and had preferable ductility and dissipative capacity under cyclic loading. The new ALBRB performs well and can be used in the aseismic design of space structures.One of the underlying requirements of BRBs is avoiding both overall and local buckling until the brace member reaches the target displacement and ductility.This required performance becomes important as the weight of the BRB and the strength and rigidity of the restraining member are reduced.Further experimental and analytical investigation is necessary to examine the overall buckling prevention conditions of ALBRBs,taking into consideration different gap sizes,BRM types,and frictional response effects in ALBRBs.

    • Prediction Model Framework for Assessing Liquefaction induced Lateral Deformation Based on Seismic Damage Investigation Data

      2014, 36(1):504-509.

      Abstract (759) HTML (0) PDF 298.41 K (1581) Comment (0) Favorites

      Abstract:This paper presents a framework for assessing the probability that a specified liquefaction-induced lateral deformation will be exceeded based on seismic damage investigation data.This framework overcomes the defect in traditional empirical formulas and regression models in how the terms of uncertainty are described.It deals not only with the effect of liquefaction but also with the probabilistic characterization of all possible region ground motions at a given site with a known earthquake history (in terms of the joint distribution of PGA and MW).In the case analysis,we obtain a liquefaction-induced lateral deformation hazard curve by applying the framework to the calculation in order to demonstrate the annual rate of deformation exceedance at a given site for a given exposure time.Thus,this framework has the potential to be a very useful tool in the field of geotechnical earthquake engineering.It can also facilitate further research efforts to describe the uncertainties associated with liquefaction induced lateral deformation.While the proposed framework is simple and effective,more work is necessary,especially on other factors that may be influencing the deformation,before it may be considered to be complete.

    • Prediction Model Framework for Assessing Liquefaction induced Lateral Deformation Based on Seismic Damage Investigation Data

      2014, 36(1):504-509.

      Abstract (697) HTML (0) PDF 0.00 Byte (0) Comment (0) Favorites

      Abstract:This paper presents a framework for assessing the probability that a specified liquefaction-induced lateral deformation will be exceeded based on seismic damage investigation data.This framework overcomes the defect in traditional empirical formulas and regression models in how the terms of uncertainty are described.It deals not only with the effect of liquefaction but also with the probabilistic characterization of all possible region ground motions at a given site with a known earthquake history (in terms of the joint distribution of PGA and MW).In the case analysis,we obtain a liquefaction-induced lateral deformation hazard curve by applying the framework to the calculation in order to demonstrate the annual rate of deformation exceedance at a given site for a given exposure time.Thus,this framework has the potential to be a very useful tool in the field of geotechnical earthquake engineering.It can also facilitate further research efforts to describe the uncertainties associated with liquefaction induced lateral deformation.While the proposed framework is simple and effective,more work is necessary,especially on other factors that may be influencing the deformation,before it may be considered to be complete.

    • Numerical Analysis of Screening Efficiency of DrivenPiles in Different Layouts

      2014, 36(1):510-515.

      Abstract (782) HTML (0) PDF 359.99 K (1129) Comment (0) Favorites

      Abstract:While rapid development of high-speed railways brings convenience,it also causes vibration impacts on the surrounding ground that need to be mitigated.The study of using driven piles as a vibration isolation method is almost in the stage of theoretical analysis.In this article,the train load is represented by the Fourier expression form that can be used in finite element calculation,and the three-dimensional piles vibration isolation model is created with ABAQUS finite element software.The different factors of the vibration isolation effect are analyzed using the control variable method,and these factors include the pile length,spacing,material,double row distance,and arrangement.The results can provide the basis for a construction design.

    • Cyclic Elastoplastic Constitutive Model of Clayey Sand and its Dynamic Numerical Analysis

      2014, 36(1):516-524.

      Abstract (709) HTML (0) PDF 473.34 K (1212) Comment (0) Favorites

      Abstract:The definitions of overconsolidation state parameter R and structural property state parameter R* are perfected, and a new derivation of the super/subloading yield surface model is offered based on these definitions. The numerical implementation based on this unified constitutive model is compiled, and the simulation is carried out. The mechanical characteristics of clay and sand and the differences between their state parameters are analyzed. The numerical implementation of clayey sand is then simulated based on the theoretical analysis. To find the correspondence between the numerical parameters and the clay content, simulations of clayey sand with varying parameters are carried out.

    • Improvement of Spring Constant Calculation in ResponseDisplacement Method

      2014, 36(1):525-531.

      Abstract (850) HTML (0) PDF 211.34 K (1190) Comment (0) Favorites

      Abstract:When the response displacement method is adopted for the seismic calculations of underground structures,the key is to determine the soil spring constant, as spring constant values directly affect the calculation results.Based on the existing static finite element method of calculating the spring constant,six variations of this method are designed through different applications of force,and their calculation results are compared. The calculation results of the whole solution and the whole simultaneous solution of the radial and tangential spring constant methods should be dangerous,the single solution and the single simultaneous solution of the horizontal and vertical spring constant methods possess high computational precision,and the calculation results of the whole solution and the whole simultaneous solution of the horizontal and vertical spring constant methods show be safe.

    • A Comparison of the Seismic Responses at Different Sites byTwo Analysis Programs under Weakly Nonlinear Conditions

      2014, 36(1):532-539.

      Abstract (806) HTML (0) PDF 248.93 K (933) Comment (0) Favorites

      Abstract:The one-dimensional equivalent linear method for soil layer seismic response analysis is widely used in engineering practices and academic fields. LSSRLI-1 and SHAKE2 000 are typical codes.LSSRLI-1,which represents the 1980s skill level,is recommended in Chinese manuals on seismic safety evaluation practices.SHAKE2 000 represents a more internationally advanced level.Improvements to LSSRLI-1 must be made with respect to the drawbacks of the equivalent linear method it uses.To reveal the differences between LSSRLI-1 and SHAKE2000,we established a horizontal layered model for class-Ⅰ to class-Ⅳ sites.Then we ran the two programs on the same working cases.A comparison and statistical analysis of the results shows the difference between the two programs and we therefore propose a variation of the relative deviation rule.Results indicate that peak ground acceleration (PGA),the spectrum,and the shear strain results do not obviously coincide in class-Ⅲ and class-Ⅳ site conditions. But in class-Ⅰ and class-Ⅱ sites conditions,there is little difference between the results of the two programs.After preliminary analysis,we conclude that the shear strain calculation method can be improved by modifying the shear modulus method to narrow the gap between LSSRLI-1 and SHAKE2000 results.We make this conclusion on the basis of the relative relationships between the shear strain,the PGA,the spectrum,and the shear modulus relative deviation.

    • Analysis of Numerical Simulation of Liquefiable Silty Soil Reinforced by Gravel Pile

      2014, 36(1):540-543,554.

      Abstract (697) HTML (0) PDF 409.92 K (1082) Comment (0) Favorites

      Abstract:The gravel pile technique is currently one of the most effective,economical, and widely used methods for dealing with saturated silt soil foundations.Many scholars have conducted research on the gravel pile mechanism with respect to saturated silt or sand foundations,and they have found some useful conclusions.However,further analysis is required on the seismic liquefaction characteristics of gravel piles in saturated silty soils.In this paper, we investigate the seismic liquefaction characteristics of gravel pile in the silt foundations of a number of Anhui expressway roadbed engineering projects.We performed numerical analysis using the three-dimensional finite difference program FLAC3D.By studying the pore pressure increase and the law of dissipation at different distances from the gravel pile center,we determined the reasonable pile space and the reasonable depth of gravel pile strengthening in a saturated silty soil foundation during high-intensity earthquake conditions.These results can provide reference data for similar engineering projects.

    • Experimental Study on Liquefaction Depth of Saturated Silty Soil Ground under Seismic Loading

      2014, 36(1):544-548.

      Abstract (768) HTML (0) PDF 879.31 K (1779) Comment (0) Favorites

      Abstract:To obtain the corresponding maximum liquefaction depth of saturated silty soil ground under different seismic shock conditions,we studied the liquefaction behavior of saturated silty soil under various seismic loading conditions at different depths.We conducted a series of GDS dynamic triaxial tests to consider different dynamic loads which were set in advance,and determined the degree of silt soil liquefaction at different depths and different seismic shock conditions.We also obtained the relationship between the dynamic shear stress ratio and the number of soil cycles.We established liquefaction depth according to the discriminate formula.The results can be used to predict soil liquefaction depths for high seismic intensity area projects.

    • Stress Characteristics of Soil around the Pile of a MonopileFoundation in Offshore Wind Turbines

      2014, 36(1):549-554.

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      Abstract:The mechanical behavior of soil plays a significant role in the deformation and stability of the pile foundations of offshore wind turbines.The soil’s stress path around the pile foundation is complex under the wind and wave loadings.This paper conducts a numerical simulation for a simplified pile foundation using the finite element method (FEM),and studies the deformation,stress path,and rotation mode of the principal stress axes under cyclic loadings.We found that the soil’s stress components around a pile foundation show periodical variation with an increasing number of cycles.The stress path in the first cycle is significantly different from that in subsequent cycles. We observed a marked repetitive rotation of the principal stress axes in the shallow region of the soil foundation and the rotation amplitude that it can reach.

    • Determination and Hazard Evaluation of Seismic Liquefaction

      2014, 36(1):555-561.

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      Abstract:Earthquake liquefaction of saturated sandy soils may induce severe damage,and this issue has become an important research topic in the field of soil dynamics.To judge the potential for earthquake liquefaction and to evaluate liquefaction hazards can lead to better control and prediction of liquefaction.Liquefaction discrimination may be considered first by making a preliminary judgment.Preliminary judgment,according to available survey data or a simple testing method,may provide a determination of the initial level of soil liquefaction.Further discrimination is necessary for soil layers where earthquake liquefaction may occur,as determined by the preliminary judgment.Since there are many factors affecting soil liquefaction,we recommend an empirical method that includes the standard penetration test,the static cone penetration (static sounding)test,and the shear wave velocity method.The single discrimination method has limitations in its scope of application;therefore,a combination of various methods is more reliable.Liquefaction hazard evaluation adopts a harmfulness index to analyze the degree of harm caused to buildings by liquefaction.Evaluation methods mainly include the liquefaction index method,the seismic settlement value method,the spectrum intensity ratio method,and the synthetic method.Based on the evaluation index,a comprehensive liquefaction ranking can fully reflect the potential and extent of the liquefaction hazard.

    • Study on Tensile Properties of Remolded Loess in Jiuzhou Development District,Lanzhou,China

      2014, 36(1):562-568.

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      Abstract:Loess is a typical water sensitive structural material with relatively low tensile strength. Under most circumstances in engineering practice,the tensile strength of loess and most geomaterials is negligible.However,there are many earth structures(slopes,subgrades,and tunnels)damaged due to tensile stresses.So the tensile properties of loess become very significant for practical engineering.The shear,unconfined compressive,and tensile properties of remolded loess taken from Jiuzhou Development District in Lanzhou,China, are thoroughly investigated in this study using the undrained triaxial shear test,unconfined compressive test,and unconfined penetration tensile test.The relationships among the tensile strength,shear strength,and unconfined compressive strength of the remolded loess are comparatively analyzed.The test phenomena show that the shear test specimen under low confining pressures fails in a brittle pattern,while under high confining pressures,it fails in a plastic pattern,and that the plasticity seems to grow with the increasing of the water content of the loess.The specimen in the unconfined penetration test fails in a brittle pattern,splitting into two or three petals with peak tensile stresses.The axial tensile stress first increases to a maximum value with the increasing of penetration depth and then has a steep decreasing process with the continued increasing of penetration depth.The test results indicate that the tensile strength of remolded loess decreases in a quadratic polynomial pattern with the increasing of water content,and the degree of correlation is satisfactory.By comparison and analysis,it is shown that the tensile strength of remolded loess is much smaller than the unconfined compressive strength,and the unconfined compressive strength tends to increase with the tensile strength in a linear pattern.The ratio of tensile strength to compressive strength first decreases,then increases,and finally decreases again as the water content increases;however,it increases,then decreases,and finally increases with the increasing of dry density.The maximum ratio of tensile strength to compressive strength occurs around the optimum water content and maximum dry density,while the minimum ratio of tensile strength to compressive strength appears to be at the maximum water content and minimum dry density.Cohesion and internal friction angle are the two indicators of the shear strength of soils,and they are affected by the structural and strength characteristics of soils.Regression analysis on the shear strength,unconfined compressive strength,and tensile strength suggests that the cohesion of the remolded loess decreases with little amplitude at first and then increases approximately in a monotonic linear pattern with the unconfined compressive strength and tensile strength.Both the unconfined compressive strength and tensile strength increase exponentially with the product of cohesion and tangent of internal friction angle.Similar to the water content,the degree of saturation of loess also has something to do with the strength characteristics of loess.The test results indicate that both the unconfined compressive and tensile strength decrease with the increasing of the degree of saturation in a polynomial pattern.

    • Discussion of the Selection of Initial Values for Rock Spectrum Parameter Inversion Based on the Least Squares Method

      2014, 36(1):569-574.

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      Abstract:Spectral induced polarization (SIP) is an effective means to explore an induced polarization target and deep minerals in geophysical prospecting. Induced polarization (IP) is a geophysical imaging technique used to identify subsurface materials, such as ore. The method of IP is similar to electrical resistivity tomography, in that an electric current is induced into the subsurface through two electrodes and voltage is monitored through two other electrodes. IP is a measure of a delayed voltage response in earth materials. The IP effect is caused by a current-induced electron transfer reaction between electrolyte ions and metallic luster minerals and is a measurement of the electrical energy storage capacity of the earth. The IP effect can be determined by passing an induced current into the ground and measuring the change in voltage with respect to time (TDIP), or by measuring changes in phase at a given frequency with respect to a reference phase (FDIP). To produce an IP effect, fluid-filled pores must be present, since the rock is essentially an insulator. The IP effect becomes evident when these pore spaces are in contact with metallic luster minerals, graphite, clays, or other alteration products. IP effects make the apparent resistivity of the host rock change with frequency. Generally, the rock resistivity decreases as the measurement frequency increases. Understanding the rock spectrum parameters, which are obtained through resistivity and phase inversion, is the most important step. There are many methods applied in rock spectrum inversion. Generally, when using the least squares algorithm, the inversion result is primarily determined by the initial value of each parameter. In this paper, the authors will show that the initial value based on the least squares algorithm can be selected randomly from the scope of various parameters. In order to demonstrate the practicality of this method, the theoretical data determined by Luo Yan-zhong is compared to shale measurement data (complex resistivity and phase) measured by an SI-1260A Impedance Analyzer. The shale was saturated before starting the experiment and the measuring conditions were room temperature and standard pressure. During the measurement, the frequency was applied at a total of 61 points, varying from 0.01 Hz to 10 kHz and the measuring mode was a symmetric quadrupole. In order to prevent the partial saturation fluid to evaporate and alter the electrical characteristics of the rock samples, both of the shale core's ends were soaked in the saturation fluid. In order to reduce the electrode polarization effects, the annular high-purity platinum network was used as unpolarized electrodes. In order to reduce noise disturbance, each core was measured a minimum of three times until the error of two adjacent measurements was within the permissible range. The experiment was automatically controlled by a computer during the entire process. Impedance and phase parameters were obtained from the experiment. Complex resistivity could be calculated through the impedance according to the geometric parameters of the shale cores. The single and double Cole-Cole models are selected to study the complex resistivity properties of shale. The inversion results show that the complex resistivity and phase curves can be described well and the spectrum parameters also can be obtained precisely. Simultaneously, relative to blindly selecting the initial value, this method has the advantages of avoiding local minima and performing at a high speed, and it overcomes the previous detrimental impact on the results.

    • Finite Element Analysis of Reducing the High speed RailwayVibration Effect on the Environment Using Open Trenches

      2014, 36(1):575-579.

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      Abstract:The high-speed railway vibration effect on the environment has become more and more widespread in recent years,and technical measurements are needed to minimize the damage to the environment caused by this new transportation vehicle. It has been shown that open trenches can be used for this purpose because of their easy construction and relatively good isolation effects. The finite-element software ABAQUS was adopted to analyze the open trench isolation effects.In order to adequately absorb the shock wave and reduce the impact of border-reflected waves on the results, the infinite element and visco-elastic boundary is used in this model.The parameter ARF is introduced in the calculation procedure so as to evaluate the isolation effects.The reduction effect of different factors that influence the resulting vibration reduction,such as the different sizes of an open trench and the frequency of the vibration load,are also discussed.The obtained approaches can be applied by designers in this area.

    • Dynamic Properties of Soil in Intertidal Zone under Cyclic Lifting Loads

      2014, 36(1):580-584.

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      Abstract:A series of dynamic triaxial tests of soil samples from intertidal zone were performed under strain-controlled and stress-controlled conditions respectively.The relationships among stress,strain and pore pressure of soil samples under cyclic lifting loads were obtained,and the dynamic properties and liquefaction potential of the foundation soil were analyzed.Finally,some suggestions about construction methods in site were proposed.

    • Research on Slope Stability Safety Factors of a High Earth rock Dam under Seismic Conditions

      2014, 36(1):585-591.

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      Abstract:The current design code for earth-rock dams (DL/T5395-2007)specifies that it applies only to earth-rock dams up to 200 m in height. With new developments in dam design and construction technology,design safety standards must be established for slopes of earth-rock dams more than 200 m high. Based on the theory of relative safety, the reliability index and safety factors associated with mapping should have the same platform.The permissible slope stability reliability indicator for a rolled earth-rock dam less than 200 m high, as specified by the current design code,is 4.2.Based on risk management principles,an allowable slope stability reliability indicator for a 200~250 m high earth-rock dam is 4.45,and that for a 250~300 m high earth-rock dam is 4.7.The corresponding slope stability safety factors for high earth-rock dams under seismic condition are 1.35 and 1.4,respectively.Slope stability safety factors for high earth rock dams under various seismic conditions were shown to meet safety standards.

    • Research on the Influence Factors of Vibration dueto Metro Shield Construction

      2014, 36(1):592-598.

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      Abstract:This study focusess on the shield construction of Beijing subway line 8 under typical working conditions,using the field monitoring system at the shield construction work face,to obtain the amplitude and frequency characteristics of the vibration source.Based on these characteristics,we conducted a sensitivity analysis of the factors influencing the vibration source. We first used the grey relation entropy method,and then performed multiple regression analysis on the vibration induced by the metro shield construction.The research results are as follows:(1) we propose that the main controlling factor of the shield construction vibration source-the stratum condition and its quantization characteristic parameter-is the weighted dynamic elastic modulus of the tunnel face stratum,and the main construction parameters influencing the vibration are the cutter head torque and the gross propulsion;(2)we establish a regression model of the shield construction vibration source which shows remarkable correlations.These research results may be used as a basis for analysis,forecast,and construction with respect to controlling of the environmental vibration response caused by shield construction,which fills a void in this area of research.

    • Focal Mechanism of Small and Moderate Earthquakes and Tectonic Stress Field in Sichuan-Yunan Areas

      2014, 36(1):599-607.

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      Abstract:Seismic activity is the direct reflection of tectonic stress fields.Under a regional stress field,the cumulative strain reaches a certain level before the crustal rock fractures and is dislocated,resulting in an earthquake.The accumulation of tectonic stress follows the temporal variation and spatial migration of the stress field.The study of stress field trends in wide regions may determine the epicenters of future large earthquakes to provide a scientific foundation for the physical meaning of earthquake prediction.Current research methods of tectonic stress fields mainly include geological structure analysis,seismic analysis,in-situ stress measurement,numerical simulation,and experimental simulation.The most direct method for reflecting the stress state of the crust is to examine the focal mechanism of earthquakes in the deep crust.Compared with strong earthquakes of lesser quantity and concentrated distribution,small and moderate earthquakes are numerous and widespread;these conditions provide the possibility of detecting the stress state of the crust in the study area.Some of the most intense seismic activities in China have occurred in Sichuan-Yunnan,located in the southeastern region of the Tibetan Plateau.Several large earthquakes have occurred in this area during the past 30 years,and its unique tectonic environment has a specific meaning in the dynamics of the continent. In this paper,we calculate the focal mechanism of 1893 M≥3.0 small to moderate earthquakes that occurred from 2003 to 2012 by using the Hash method on the basis of P-wave first motion and S-wave amplitude ratios,and we analyze their characteristics.Moreover,we investigate the focal mechanisms of moderate and strong shocks occurring from 1976 to 2012.The regional stress field is inverted by using the spatial and temporal stress inversion (SATSI) method for damping regional stress with 1651 reliable focal mechanism solutions, and its space characteristics are analyzed.Our research shows that the focal mechanism solutions of small and moderate M≥3.0 earthquakes were dominated by strike slip from 2003 to 2012 in the Sichuan-Yunnan region,with some reverse and normal faulting M≥4.0 earthquakes were dominated by strike slip,which is consistent with the regional background.The fault type is indicative of 3.0 ≤M≤3.9 random earthquakes.The Sichuan-Yunnan area is divided into five zones of A,B,C,D,and E according to geological and seismic activity and other characteristics to examine the characteristics of the focal mechanism in detail.The results show that characteristics differ among zones.The stress action is mainly horizontal,and strike-slip faulting is dominant in the study area.The maximum horizontal principal stress orientation of the tow side of the Hong-he fault tail is NW-SE.In the Sichuan-Yunnan area,the rhombic block stress is divided into two different states by the Lijiang-Xiaojinhe fault;the stress orientation of the south region is NW-SE,and that of the north region is N-S.The stress orientation has a rotating clockwise tendency from inner the Tibetan Plateau to the east border of the Sichuan-Yunnan rhombic block.In the eastern boundary area,there is a gradual transition from NE to SW in the north to NW-SE in south.The maximum horizontal principal stress orientation is parallel to the fault orientation in western and southwestern Yunnan.We compared our results with the Harvard Centroid Moment Tensor (CMT) database and determined that our results are comparatively accurate.

    • Study of Attenuation Characteristics, Site Response and Seismic Source Parameters of the Pubugou Reservoir Region

      2014, 36(1):608-615.

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      Abstract:On the basis of digital seismograms recorded by the Pubugou reservoir digital seismic network, we obtained the nonelastic coefficient of Pubugou reservoir area by using the method proposed by Atkinson. The site response of each station was obtained by using the Moya method. The frequency-dependent Q(f) at the reservoir area is estimated as Q(f)=47.1*f0.92; the site response of each station is approximately 1.0, showing little amplification. On the basis of the Q(f) and the site responses, we detected approximately 67 tectonic earthquakes and 208 source parameters of blasting shocks by using the Atkinson inversion method. The results show obvious differences in the source parameters of the tectonic earthquakes and blast shocks. The parameters near the reservoir dam area and Hanyuan County were lower because of the blasting vibration.

    • Effects of Potential Earthquakes on Construction and Development in South China Sea Region

      2014, 36(1):616-621.

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      Abstract:The South China Sea (SCS)region is rich in oil,gas,and fishery resources,as well as potential tourism sites.With the establishment of the city of Sansha,traffic engineering,civil engineering,and infrastructure construction in the SCS have become the core of the economy.The SCS is located at the intersection of the Eurasia,Pacific,and Indian Plates and has a very complex geological structure.Considering the impact of potential earthquakes on the development of the SCS region,steps need to be taken to mitigate their dangerous effects.China currently has established relatively complete seismic design codes for structures on land,but studies on offshore earthquake engineering are still rare,and attenuation strategies for offshore engineering are incomplete.This paper will analyze the seismotectonics of the SCS and its adjacent areas through analysis of historical seismic data.The results show:(1) Earthquakes greater than magnitude 7 have occurred in the northern part of the SCS.Thus,offshore engineering in the region should consider the impact of earthquakes related to the Honghe and Qiongyue offshore fault zones. (2) In the central region of the SCS,the impact of the subduction zone from south Tainan to the west side of the Luzon Island in the Philippines should be taken into account. (3)The characteristics of subduction earthquakes and shallow crustal earthquakes are different,and it is necessary to study the specific features of interface and intraslab earthquakes in a subduction zone.

    • Fault Parameters and Slip Properties of the 1954 Northern Tengger Desert M7.0 Earthquake

      2014, 36(1):622-627.

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      Abstract:The northern Tengger Desert M7.0 great earthquake that occurred in 1954 resulted in varying degrees of damage in many areas of Neimenggu and its adjacent regions.Thus far,research results of the cause of this earthquake are few and inconsistent.Because it occurred in the Gobi Desert,the aeolian effect of was intense.These facts cause difficulties in studying the earthquake through geological prospecting methods.It is known that clustered small earthquakes often occur in the fault plane vicinities of large earthquakes.We used precisely relocated earthquakes that occurred near the earthquake rupture zone between 1985 and 2012 and selected a strip-shaped zone according to clustered small earthquakes and long-axis morphology in the meizoseismal area.On the basis of simulated annealing and Gauss-Newtonian nonlinear inversion algorithms,we obtained fault plane parameters of earthquakes such as strike,dip,and location by using data of densely populated small events.On this condition,rake angles of the fault plane are further inferred from regional tectonic stress parameters.Finally,we determine that the inverted results and known results are similar and that the former are in the cycle of the highest seismic intensity.These findings indicate that the inverted results are reliable.

    • Preliminary Analysis of Coseismic Response of Tiltmeters with High Sampling Rate Used at Huzhou Seismostation

      2014, 36(1):628-633.

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      Abstract:By comparing the response characteristics and seismic phase parameters recorded by VP, SSQ second sampling tiltmeter and JCZ-1T seismometer in the same period of the earthquake, this paper presents that the three instruments can all record clear P wave, S wave and surface wave, and S wave recorded by VP and JCZ-1T is clearer than that recorded by SSQ. Bandwidth of seismic waves recorded by VP is more consistent with that of JCZ-1T records. Before the Iran and Pakistan boundary M7.7 earthquake on April 16, 2013, JCZ-1T seismometer and SSQ tiltmeter simultaneously record a slowly moving event at intervals of 15~30 s.

    • Characteristics of Horizontal Deformation Field of the Shanxi Seismic Zone before and after the Wenchuan M8.0 Earthquake

      2014, 36(1):634-638.

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      Abstract:We obtain the horizontal velocity field and tectonic strain rate field of the Shanxi seismic zone derived from Global Positioning System(GPS) data before and after the Wenchuan M8.0 earthquake.The results indicate that after the Wenchuan M8.0 earthquake,the velocity of each region in the Shanxi seismic zone deflected westward in varying degrees.The north area including Taiyuan Basin shifted to SWW from SW and SSW directions in 1999-2007,and the velocity developed from an average of approximately 2 mm/a to 4 mm/a. In addition,the area south of Taiyuan Basin shifted to SW from a SSE direction.The strain rate field in the Shanxi seismic zone was significantly enhanced after this earthquake and formed three compressive strain concentration areas in Datong Basin,north Taiyuan Basin,and southwest Linfen Basin.In these respective areas, the Datong M4.5,Yangqu M4.6,and Hejin M4.8 earthquakes occurred in 2010.These earthquakes may have occurred because a regional stress field environment with compressive strain accumulation is beneficial to the formation and occurrence of a moderate earthquake in the Shanxi seismic zone.Moreover,because of the Japan M9.0 earthquake,the westward velocity of the Shanxi seismic zone was weakened,and the strain rate field expanded obviously during 2009 to 2011.In addition, the velocity in the north area including Taiyuan Basin decreased to approximately 2~3 mm/a,and the area south of Taiyuan Basin moved toward the south from the SW direction.This area may return to the background velocity of that during 1999 to 2007 in the future.

    • Characteristics of Gravitational Field Anomalies prior tothe Yuanping M4.2 Earthquake in Shanxi

      2014, 36(1):639-644.

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      Abstract:On March 28,2009,an earthquake of M4.2 occurred in Yuanping in Shanxi Province that affected people’s residences 200 km the epicenter area.The epicenter was at middle part of Yiding Basin,which is a horseshoe-shaped extensional basin,and the edge faults of the basin include the northern Wutaishan,northern Xizhoushan,eastern Yizhongshan,and southern Henshan faults.In this study,we collect the gravity data of the Portable Gravity Observation Network from 100 observed points distributed in the Shaxi-Inner Mongolia region during 2007—2009.The values of gravity field variation with time are calculated in terms of six months and one year at every observed point,and values at every network point are obtained by interpolation with kriging and trend extrapolation methods in that region. Analysis of gravity variation characteristics prior to the M4.2 Yuanping earthquake shows that the gravity field data in the epicenter area exhibited negative banded anomalies in the E-W direction before the M4.2 earthquake and those positive anomalies appeared both north and south of the epicenter zone.The observed gravity field values show characteristics of ascent-descent-restitution at most observation stations near the epicenter.The Yuanping earthquake occurred during the restitution period.The varied characteristics of the gravity field described above did not appear in gravity observation points in the Inner Mongolia region far from the Yuanping epicenter zone.The Yuanping epicenter is located in a negative anomaly zone of the Bouguer gravity gradient and in a negative gradient anomaly zone of variation of Bouguer gravity,which corresponds with the northern Wutaishan Fault.This phenomenon implies that a corresponding relationship existed between gravity changes and tectonics in the study area Due to media inhomogeneity of the earth,earthquakes cause different areas to exhibit varied values of media density,which is generally more obvious near the faults.It is widely accepted that variation in the gravity field can be deduced from changes in media density and can be observed at the surface.Seismogenic body impending is a basic physical process of seismogenic theory.During the process of seismogenic body impending,media density in the focal zone is reduced;therefore,the gravity field value would decrease at the Yuanping epicenter.This reduction in media density may have caused the gravity field values observed at Yuanping epicenter prior to the earthquake occurrence.In addition, the epicenter is generally near the largest gravity change zone between ascending and descending variations.Moreover,the epicenter does not coincide with the largest position change of gravity field variation.These results support that the shape of the Bouguer gravity field gradient varied with time before the earthquake occurrence according to the seismogenic body impending theory.

    • Seismic Hazard Assessment for Active Faults of Longnan City

      2014, 36(1):645-655.

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      Abstract:Based on active fault mapping in Longnan City,Gansu Province,we determine in this study parameters used in seismic hazard assessment for active faults.Five main fault zones are identified.The first is the Diebu-Bailongjiang fault zone,which ruptured during the M7 earthquake in 186 BC.The second is the Guanggaishan-Dieshan fault zone,which is separated into three main strands.The north strand had been found to cause a paleo earthquake,although the Pingding-Huama strand had a significantly faster slip rate.The Hanan-Qingshanwan-Daoxizi fault zone is the third.A surface rupture of approximately 3.5 km long was found in the Zhuyuanba strand.The fourth is the Lianddang-Jiangluo fault zone,which had strong activity in the Holocene.The fifth is the Wudu-Kangxian fault zone,in which four paleo-earthquakes have occurred since the Late Pleistocene.We estimated potential maximum earthquake magnitude and repeat interval time with magnitude rupture length and magnitude-frequency relationships for every fault or fault sub-area.The probability of destructive earthquake occurrence in the future 50,100,and 200 years was computed with a time-dependent seismic potential probability model and a Poisson distribution model.The methods for estimating potential maximum earthquake magnitude include four principles:(1)maximum magnitude can be an upper limit magnitude in the same seismic zone and (2)should not be smaller than the largest historical earthquake.(3)It can also be estimated by a relationship,such as M-L and G-R.Moreover,(4) it may have a reference to the maximum magnitude in a seismic zone with intensity of VIII degrees during the 200 years since last big earthquake because the lapsed time is longer than the interval time.The article gives mean maximum magnitudes,which are 7.5,7,7,7,and 6 for the Diebu-Bailongjiang,Guanggaishan-Dieshan,Liangdang-Jiangluo,Wudu-Kangxian,and Hanan-Qingshanwan-Daoxizi fault zones,respectively,with a combination of the four principles.We also used the method of b value spatial mapping to reveal high stress or high seismic hazard zones.On the basis of the seismic gaps identified,we used the relationship between magnitude and number or frequency to compute the b value of the study area with small earthquakes of the most recent 40 years.The small earthquakes were relocated with seismological methods.If the area had a lower b value,lower strain was accumulated in the area.We determined higher strain areas from the b value map;such areas are future high seismic hazard zones.We used the maximum curvature method to determine minimum magnitudes of completeness,which are minimum magnitudes of earthquakes for computing the b value.We used a 1° × 1° grid for the study area.Every node had a b value that was calculated with at least 50 selected small events.The events for computing the b value were selected by a circle with a particular radius and a node center point.The results indicate that the west Guanggaishan-Dieshan fault zone has a higher potential for seismic hazards in the future; therefore,more attention should be paid to this area.Although many methods were used to prevent error in the results,many unknown parameters remained,which caused our results to have uncertainties.

    • Probability Seismic Hazard Analysis Considering the Near-fault Directivity Effect and Nonlinear Site Response

      2014, 36(1):656-662.

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      Abstract:This paper presents seismic response analyses,based on the equivalent linear method,of a sandy site subjected to near-fault ground motions.We investigate the effects of soil nonlinearity on the pulse characteristics of input ground motions,and explore the amplification factors for the spectral acceleration from near-fault pulse like and non-pulse-like motions. We found that input non-pulse motions can be transformed into pulse-like motions by attenuating the high-frequency component as it propagates through the soil.The input pulse motion probably remains as a pulse characteristic,and tends to have multiple pulses when the input motion includes other potential pulses.The attenuation of the amplification factor, along with the spectral acceleration of the bedrock motion,has a more significant effect on pulse-like motions than non-pulse motions.We expect that this finding is related to the strong nonlinear response of the soil caused by the pulse excitation.However,the amplification factor for a long period(e.g., 3 s),when the pulse motion is greater than 0.1 g,is larger than that of a non-pulse motion.Finally,a probabilistic seismic hazard analysis (PSHA)procedure is proposed to incorporate the coupled effects of the near-fault pulse characteristic and the nonlinearity site response.

    • Supplement Textual Research on Historical Data of the 1884 Ninger Earthquake in Yunnan Province and Discussion on its Seismogenic Structure

      2014, 36(1):663-673.

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      Abstract:Based on the historical earthquake reports of the Ninger earthquake in the Yunnan province on November 14,1884,and a site inspection,new information has been obtained about this historical earthquake,providing credible evidence for the improvement of the isoseismal line.This paper thus reevaluates the Ninger earthquake parameters.The historical earthquake material is primarily from Guangxu Memoir and the memorial to the throne of the Palace,as well as the historical material of local chronicles.The results show that the epicenter was located near Puer mansion (presently Ninger), which is 23.1°N,101.0°E.The accuracy is class 1,with an average error less than or equal to 10 km;the earthquake magnitude was 6.75;the epicentral intensity was Ⅷ.The most damaged area in this earthquake was Puer mansion.The damage scope was limited,and the epicenter zone can be delineated within 30 km from Puer mansion.The aftershocks were frequent and lasted for almost one month.It was a typical mainshock-aftershock earthquake.The early frequent seismic activity and continued aftershocks,as well as the relief activity of the local government and the Qing court,reveal that the magnitude of this earthquake was high and the damage was severe.The isoseismal line damage area of this earthquake pointed northwest,and the long axis of the earthquake-sensitive area pointed northeast.There is a marked difference between those two areas. Yunnan is located on the east edge of the continental border of the Indian and Eurasian plates.There are two force components acting on the Yunnan region.One is the strong lateral pressing of the Indian plate,and the other is the SSE squeezing force related to the plate activity.The east fault activity of the Yunnan region is closely related to the squeezing force.Analysis of seismogenic structures shows that the Puer fault is a seismogenic structure of this Ninger earthquake.The geometric position of the Ninger earthquake in year 1884 overlaps with the position of the Puer fault,and it is located among the checkerboard made of the NNW-trending Puer fault and a series of NEE-trending faults.Because the lateral offset of the Puer fault and the left offset of the NEE-trending faults,the earthquake of MS6.75 happened in 1884 in Ninger.The Puer fault belongs to the Simao secondary block,which is located between the Longling-Lancang River fault and the Red River fault.The trend of the long axis of the meizoseismal damage area runs parallel to that of the causative fault.Between the NNW-trending Puer fault and the Mohei fault,there exist multiple NEE-trending parallel fracture belts,which are small-scale,have poor continuity,and form in groups with a left-lateral dislocation.These grouped parallel faults formed a checkerboard fault block.An MS6.4 earthquake occurred approximately 3 km south of Ninger on June 3,2007. Studies of this earthquake showed that main characteristics of the northwest nodal plane were a right-lateral thrusting slide and those of the northeast nodal plane were left slip. Thus, the right-lateral slide of the NNW-trending Puer fault and the left-lateral dislocation led to this earthquake.Because of the fragmentized crustal structure,the region is MS6.2~6.8 earthquake-prone,and this is why there are no bigger earthquakes in this region.Due to the complicated fault structure and fragmentation,as well as the landscape and geomorphic influences,there are still uncertainties.A further detail study of the Puer fault and seismogenic structures should be carried out so as to obtain more reliable results.

    • Textual Researches for 1477 Yinchuan Strong Earthquake

      2014, 36(1):674-681.

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      Abstract:A strong earthquake occurred in the region of Yinchuan on the May 13,1477.Due to the earthquake happened at the edge of Tenggeli desert,which is a desolate and uninhabited place,historical records about this earthquake is limited.On the basis of historic documents,the magnitude of this strong earthquake was examined to be M=6 1/2,the epicenter of the west of Yinchuan(38.5°N),106.3°E, the epicentral intensity of Yinchuan was Ⅷ in all previous publication of the catalogues of earthquake in China.However,some experts have questioned the identification results,we also have problems with the magnitude and epicenter.In the paper,based on the same historical earthquake data,we use the empirical formula for estimation of seismic magnitude and elliptical attenuation of seismic intensity and some interrelated modern earthquake data;by the methods of estimating and comparing,we reanalyze the magnitude,it’s epicenter and the seismic intensity of several region of the 1477 strong earthquake. In our opinion,we recommend that the magnitude of the earthquake should be identified as M=7 1/4 ,the epicenter should be located in the east of Minqin(38.40°N,104.36°E).In addition,the epicentral intensity of Yinchuan is advised to be Ⅶ,and Zhangye is Ⅵ. Finally,combining with the proposal epicenter location,we simply discuss the seismogenic tectonic background of 1477 earthquake.

    • Preliminary Study on the OLR Anomalies Based on the Cycle Process of Celestial Tide Forces: A Case Study on the Xinyuan MS6.6 Earthquake

      2014, 36(1):682-687,704.

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      Abstract:Earthquakes are definitely a mechanical phenomenon in which stress plays an important role.Many researchers have conducted statistical studies on the relationship between celestial tide forces (CTF) and earthquakes that prove that CTF may trigger earthquakes when the tectonic stress of the focal zone is at a critical stage.However,a method for identifying the critical stage point has not been determined thus far.Outgoing long-wave radiation (OLR) signals have been observed prior to strong earthquakes in recent years.OLR data describe the radiation information from the top of the atmosphere,which is believed to reflect energy changes in the earth-atmosphere system that occurs prior to earthquakes.OLR has characteristics of a large coverage range.Because earthquake-related anomaly information of OLR is extracted and applied to earthquake prediction,OLR anomalies are highly useful for areas that are out of the monitoring range of the current precursory seismic networks.Moreover, these anomalies are helpful for monitoring the stress stage of tectonics.In this study,we use National Oceanic and Atmospheric Administration (NOAA)satellite data to observe OLR data provided by the National Centers for Environmental Prediction (NCEP)with 1° × 1° resolution and attempt to analyze the OLR anomalies before and after the Xinyuan MS6.6 earthquake through the periodic variation effect of CTF.The earthquake occurred at a relativity high value of CTF,which it indicates that the CTF had a trigger effect on the earthquake. These results show that one month before the earthquake,no OLR anomalies were noted near the Xinyuan area.With the passage of time,the figures of spatio-temporal evolution of OLR increase were noted as initial rising on June 25 → continued rising on June 26 → reaching the peak on June 27 → weakening from June 28 to 29 → earthquake occurring on June 30.This evolution reflects the following activities of the seismic fault under tectonic stress:micro breaking-rupture strengthening → accumulating energy (the decrease of stress) → releasing energy → shaking. These abnormal areas moved and expanded,and the earthquake occurred at northeast edge of the anomaly;the epicenter of this earthquake was not at the area of maximum abnormality.This result may be related to the geological structure and underground environment of the epicenter.These characteristics can provide some clues for determining future seismogenetic times and for tracking the locations of the epicenters. It is necessary to combine the study of CTF with that of OLR anomalies to explore the catastrophic events of seismic faults under tectonic stress and to reveal the complex processes of the energy accumulated and released during an earthquake.We should emphasize that only considering the factors of CTF and OLR anomalies according to relative statistical analysis is insufficient for launching a theoretical model to predict the time and magnitude of future earthquakes in a particular region.The current understanding of the genetic mechanism of the anomalies for earthquakes is not complete; therefore,additional case studies are needed.

    • Analysis of Underground Fluid Anomalies Prior to the Wenchuan MS8.0 Earthquake

      2014, 36(1):688-696.

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      Abstract:The Wenchuan MS8.0 earthquake caused widespread attention. To determine whether earthquakes can be predicted and whether anomalies are present before earthquakes, several scholars have previously studied a summary of the precursory data of the Wenchuan earthquake. On the basis of such previous research, the present study analyzes the anomalies of underground fluid present before the earthquake. By using the methods of medium-term anomaly, short term and imminent abnormalities, co-seismic variation, and the adjustment after the earthquake, this study analyzes the data of water radon, water level, water temperature, and flow. Using the subordinate function extraction for recognition and extraction of the medium term anomaly proved to be effective. The Wenchuan MS8.0 earthquake, with intensity up to XI, caused inestimable human and economic losses in the affected areas involving 125,500 km2 in 247 counties, cities, and districts. 69,180 people died, 374,008 were injured, and 17,406 were reported missing. More than 10 million people were affected. 785.88 million houses collapsed, and 2,421.54 million were severely damaged. The direct economic damage could substantially exceed RMB 845.1 billion. This disaster occurred for four main reasons. First, the earthquake had a large magnitude, high energy, and shallow focus. Fracturing lasted up to 90 s, and the earthquake excitation was more powerful in the fracture zones. Second, because the fracture surface continued for several hundred kilometers through the town, the earthquake wreaked havoc on the buildings. Third, the earthquake occurred in the mountains. Fourth, secondary effects aggravated the disaster. Field investigation and the precursory data research by previous scholars revealed that the Wenchuan earthquake included macro-precursor abnormalities and seismic effects. This earthquake had the largest magnitude of those occurring in north-south seismic belt in recent years. Therefore, it is necessary to summarize the Wenchuan earthquake precursor anomaly.In recent years, China’s seismic monitoring network has become denser, and the observation scale has become greater. Data have been accumulated for moderate earthquakes. In addition, many achievements have been in fundamental theories, earthquake prediction methods, and the precursory mechanism. In the history of more than 40 years of earthquake monitoring and forecasting, 20 destructive events have been predicted with varying degrees of success. Despite some progress in the method of forecasting, it is quite difficult to predict earthquakes. Therefore, earthquake prediction is still in the primary stage. Although the Wenchuan earthquake was not predicted, some abnormal fluid phenomena appeared before the earthquake. By summarizing and analyzing data after the earthquake, some scholars detected 28 credible underground fluid anomalies within 1000 km in addition to 11 suspected abnormalities and 194 coseismic abnormalities. A month after the Wenchuan earthquake, the China Earthquake Administration subsurface fluid disciplinary technical coordination group found 39 suspected underground fluid abnormalities within 1,000 km from the epicenter. According to the Sichuan Seismological Bureau of Statistics, nine underground fluid anomalies may be related to the Wenchuan earthquake. Despite an exception, it is certain that subsurface fluid exists before the earthquake anomalies. The following exception is divided into short-term, short-Pro, and coseismic anomalies, which are discussed in this paper.

    • Evaluation of Seismic Intensity Influence Field in Gansu Province and its Relationship with Terrain Factors

      2014, 36(1):697-704.

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      Abstract:The Gansu earthquake emergency command system was founded during the Tenth Five-year Plan by the Earthquake Administration of Gansu province.It was reviewed and accepted by the China Earthquake Administration and was enacted in 2007.With this system,we can first obtain the seismic intensity distribution and influence region according to the local intensity attenuation relationship and then quickly estimate earthquake casualty loss according to the seismic intensity distribution.We can then propose emergency measures and rescue plans and assist in decision-making for earthquake relief headquarters.Damage degrees of construction and lifeline engineering,including water supply, power supply,heat supply,air supply,transportation,and communication systems,differ among affected areas.Moreover,secondary disaster influences also differ,as well as casualties and financial loss.The seismic influence field examines the influence areas by different damage intensities.After an earthquake,designing and presentation of the influence field according to the earthquake parameters and formulating a relatively reasonable seismic intensity distribution range is very important for government investigation of the situation and damage distribution.The feasibility of the earthquake influence field will directly affect the rationality and accuracy of the assessment results.The calculation results of the existing evaluation system differ significantly from the actual results;therefore,the influence of the relief results also differs.The attenuation relationship model makes use of the large scale nationwide western attenuation relationship,the Gansu attenuation relationship of seismic intensity,and modified seismic intensity affecting the field model of the Gansu area in the Gansu earthquake emergency command technology system module to make fast judgment of the seismic influence field and heavy disaster area.However,differences occur in the actual attenuation relationship among areas and magnitudes due to different source characteristics,propagation media,and site conditions.In this paper,isoseismal line maps of actual earthquakes in the Gansu region were collected and compared with theoretical intensity generated by the attenuation relationship.In addition,the influence of terrain factors on the intensity influence field in study area was analyzed by using the digital elevation model(DEM).Conclusions show that the actual and theoretical seismic intensity distribution at each magnitude level differed. In general,the theoretical epicentral area is relatively small at the 5.0~5.2 level and shows subarea characteristics at the 5.3~5.9 level,whereas the theoretical intensity distribution is close to actual results at the 6.8~7.5 level.The subarea study shows that the outer major and minor axes and area of theoretical seismic influence field are greater than those of the actual values in the Qilian Mountains-Hexi Corridor region.However,except for the meizoseismal area,performance in the southeast region of Gansu is opposite.The impact of terrain factors on the intensity influence field is obvious.Higher altitude relates to higher intensity,and the intensity at the summit point is higher than that in the surrounding region.A greater slope to the epicenter relates to faster attenuation of the intensity and vice versa.There are obvious differences between actual and theoretical seismic influence fields,which should be considered in practical application.We should adjust the distribution of theoretical intensity by considering local terrain,landform,and site type to obtain a more reliable post earthquake assessment outcome.Furthermore, quantification of the site influence would better serve earthquake emergency response and rescue.

    • The Design of a Transient Filter and its Application in Local Seismic Observation

      2014, 36(1):705-712.

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      Abstract:At present,the phase of the last two stages of the digital filter in the earthquake data acquisition system can be divided into two types: minimum phase and linear phase.Phase characteristics directly affect the quality of recorded seismic waveforms. Important nonlinear characteristics of the minimum phase will lead to wave distortion,and the linear phase filter will result in an extra wave in front of the original wave.Based on the analysis of the two types of filter,a new transient filter is designed with the characteristics of both minimum and linear phases.The transient filter belongs to a finite impulse response filter (FIR),which consists of two cascaded stages,FIR1 and FIR2.The FIR1 filter stage has a decimation ratio of four.It compensates for previous filter droop and flattens the magnitude response of the pass band.The FIR2 filter stage has a decimation ratio of two. It creates a low pass brick wall filter to block aliased components of the input signal. In this paper,we introduce the detailed design method using Filter Design Toolbox and Signal Processing Toolbox in MATLAB and the characteristics of the filters,and we compare the testing data are introduced in this paper.The testing results of the seismic wave recorded in a number of local earthquakes show that the extra wave is eliminated and the first half period is not broadened.Thus,wave distortion can be minimized.The smooth interaction angle between the pass band and transition band and the slow roll off rate in the transition band are the common features of all transient filters.As a consequence, the sampling rate of the earthquake data acquisition system using the new transient filter must be increased to maintain the same frequency as that of the pass band edge.

    • The Effect of Initial Principal Stress Orientation on the Cyclic Shear Behavior of Saturated Siltehavior of Saturated Silt

      2014, 36(1):713-717,726.

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      Abstract:By using a soil static and dynamic universal triaxial and torsional shear apparatus,stress-controlled undrained cyclic torsional tests were performed on remolded saturated silt prepared by tamping methods with initial sampling water contents of 0% and 10%.The initial anisotropic consolidation conditions included an initial mean principal stress of 100 kPa,an initial intermediate principal stress coefficient of 0.5,an initial deviator stress ratio of 0.433,and principal stress initial orientation angles of 0°,30°,and 45°,respectively.During the undrained cyclic shearing process,the mean principal stress and the intermediate principal stress coefficient were fixed.We studied the effects of the initial orientation of the principal stress and the initial sampling water content on the silt’s dynamic shearing deformation,its strength,and its pore water pressure development.The test results show that the extent of the initial principal stress orientation’s effect on the remolded silt’s deformation and strength behaviors varied,and that the initial sampling water content has considerable influence on the cyclic behavior of saturated remolded silt.

    • A Comparison of Dynamic Response and Failure Simulations in Geotechnical Dynamic Centrifugal Model Tests and the Key Issues

      2014, 36(1):718-726.

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      Abstract:Focusing on two similar levels of the simulation of dynamic response and dynamic failure in the model and the prototype for geotechnical dynamic centrifuge model tests,this paper analyzes and summarizes the research and development status of the simulation of dynamic response and failure in the centrifugal model test.The implementation requirements and differences of a similar scale were analyzed in simulations of the dynamic response and failure.According to the anti-slide pile and tunnel models,the specific model-theoretical scale relationships were deduced, and the key problems of the simulation of dynamic response and failure in the dynamic centrifuge model are discussed in the paper.The existing problems and development direction of the geotechnical dynamic centrifuge model test are described.The results show that for a similar scale relationship between the model and the prototype,there is a stricter similar scale requirement for the dynamic failure model than for the dynamic response model,which is the fundamental reason that the dynamic failure simulation model can reveal the prototype failure of geotechnical structure.

    • Influence of Clay Content on Post liquefaction Characteristics of Silt

      2014, 36(1):727-733.

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      Abstract:Silt is one of the most common soils encountered in the field,and it is prone to liquefaction when earthquakes occur.In China,silt is widely located in the zones of the Qiantang River,the Yellow River,the cities of Kunming and Tangshan,and numerous other regions.The topic of silt liquefaction has been one of the hottest issues since the 1976 Tangshan earthquake.This paper presents the post-liquefaction stress-strain characteristics of silt samples with different clay contents induced by strong earthquakes.Large deformations occur during the post-liquefaction stage,which may trigger a large amount of horizontal ground movement or destroy the structure built there.It is of great importance to take precautions when confronting post-liquefaction deformation induced by earthquakes,especially on horizontal ground.Silt samples with clay contents of 3%,6%,8%,9%,12%,and 15% were used in this research.The original silt,sand,and clay samples were mixed in different mass proportions in order to obtain silt samples with different clay contents.The influence of the clay content on the degree of post-liquefaction deformation was studied by a series of monotonic tests.The test was based on liquefied silt samples by using a specially made triaxial apparatus.Large deformations can be recorded using the adequately large displacement sensors in this apparatus.These samples with different clay contents were isotropically consolidated to the specified pressure.Then cyclic loading was performed to trigger the initial liquefaction and was maintained until the specified severity of liquefaction was reached.Finally,monotonic loading was conducted to simulate the post-liquefaction stage based on the liquefied silt samples.Undrained shear tests were performed during the cyclic and monotonic loading stages.The post-liquefaction shear stress and shear strain were recorded automatically for these test results.From the stress-strain relationship of different clay contents,the 3% and 15% clay content samples showed less strain at the same stress level,and the 8% clay content sample showed the largest strain.This phenomenon can be explained as resulting from the clay content in the silt.Clay particles acted as both the lubricant and the adherent in the silt samples.As the clay content increased,the lubrication decreased and the glutinousness increased.There exists a critical clay content level,where the post-liquefaction strain reaches a maximum at a constant stress level.This explanation is consistent with the effect of clay particles in silt on the cyclic shear stress ratio.The silt sample with 8% clay content produced the minimum shear stress ratio during the cyclic loading stage and thus the maximum strain during the monotonic loading stage.The effect of the clay content on post-liquefaction characteristics can be quantifiably evaluated from our test results. As is known,the strain at nearly zero effective stress was the key strain component of post-liquefaction deformation.The relationship between deformation and the cyclic maximum strain was linear for silt samples with different clay contents.The slopes of these lines reflect the effect of clay content on post-liquefaction stress-strain.Therefore,the effect of the clay content on post-liquefaction characteristics was calculated.It was confirmed that the silt post-liquefaction stress-strain formula compared well with data collected from other tests.

    • Strong Motion Observation and Records of the Gaoyou BaoyingMS4.9 Earthquake in Jiangsu Province

      2014, 36(1):734-740.

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      Abstract:The strong motion of the Gaoyou-Baoying MS4.9 earthquake occurring on July 20,2012,was recorded by 43 of 50 strong motion stations in Jiangsu Province.The observation system of every strong earthquake station includes the Etna strong motion recorder produced by the KMI Company in addition to a domestic force balance accelerometer(FBA) sensor.These instruments effectively recorded the earthquake ground motion that occurred in Jiangsu Province by setting the appropriate threshold and transmitting the strong motion events through PSTN or CDMA wireless networks to the digital strong motion network center of Jiangsu Province.During this earthquake,the recorded maximum acceleration was 33.76 cm/s2.The earthquake epicenter was located at 33.04°N,119.57°E,and the focal depth was approximately 6 km.The microcosmic-epicenter was located in Shuanggou Village,Gaoyou City,where strong earthquake motion was felt.Tremors were felt throughout Jiangsu Province,as well parts of Anhui Province at its junction with Jiangsu Province. Fourier spectral analysis was used to determine that the seismic acceleration included abundant frequency components mainly between 2 Hz and 4 Hz. The acceleration time history and Fourier spectrum records from several strong ground motion stations are also given in this paper.Moreover, this study gives a brief introduction of the American ShakeMap system,which is the primary method used to calculate instrument intensity,and a recommended intensity scale provided.We collected recent strong earthquake records of Jiangsu Province and fit the instrumental intensity calculation formula (below intensity of VI)with these strong earthquake records.Due to the limited earthquake records in this region, however,we were unable to give a complete intensity calculation formula.Finally,two methods of producing an intensity contour map are given in addition to comparisons between approaches and conclusions.The characteristics of the seismic intensity contour are intuitive and vivid,which makes it easier to more accurately describe the distribution characteristics of earthquake damage.The results from the analysis of spectral characteristics with the strong motion records show that the peak acceleration of the horizontal component is larger than the vertical component.Moreover,the site covering of soil has an obvious amplification effect.On the basis of the strong motion records and influence of the field contour map,we obtained the peak acceleration distribution of the Jiangsu area.These result conform those of the actual investigation.The result of using the strong motion data to quickly assess the spatial distribution of seismic intensity has important significance for the earthquake emergency rescue work.Therefore,the method used in this study has a certain degree of feasibility. It is difficult to calculate instrument intensity values that are consistent with macroscopic intensity values because of objective factors such as subjectivity,and vagueness that exist in the evaluation of seismic intensity.Therefore,by selecting a suitable method for intensity evaluation of ground motion parameters and examining the seismic ground motion attenuation relationship,in addition to researching methods of field calibration for future work,the instrument intensity calculation method is proven to be scientific and reasonable.

    • Centrifugal Model Test of an Offshore Wind Turbine Foundationon Saturated Sand Ground

      2014, 36(1):741-745.

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      Abstract:With its low cost and simple structure, the bucket foundation has great application potential for the offshore wind turbine foundation. The main load of the foundation suffers horizontal cyclic loading, which we simulate in this study by an eccentric wheel and cylinder. We conduct centrifugal model tests on a saturated sand foundation in which we simulate and measure the stress, deformation, and pore pressure. We then analyze the deformation and stress characteristics of the bucket foundation according to the measurement results, which show that dumping destruction obviously occurred under monotonic and cyclic horizontal loads, and deformation appeared mainly around the bucket foundation.

    • Research on the Residual Deformation of Sandy Soil of Land Reclamation in Airport Industrial Park in Dalian

      2014, 36(1):746-752.

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      Abstract:We conducted dynamic characteristic tests on sandy soil samples collected from Dalian Airport Industrial Park,adopting the DSZ-1-type electromagnetic vibration triaxial apparatus developed by Engineering Mechanics,China Earthquake Administration.Sandy soils are characterized by strong permeability,high shear strength,small deformation,and subsidence.This test investigated the dynamic residual deformation characteristics of two types of sand(i.e.,shallow and deep sand)under a complex stress state.Increasing the dynamic stress ratio and confining pressure improved the residual volumetric strain and residual shear strain,and the influences of both quantities on both strains could be described by the same law.However,the consolidation ratio was reduced by increasing the residual volumetric strain,and increased by increasing the residual shear strain.While the consolidation ratio of residual volumetric strain significantly affected the fitting results,that of the residual shear strain exerted small impact.The influences of consolidation ratio on the residual volumetric strain and residual shear strain were significantly different.The Cvr was linearly related to the dynamic strain amplitude of residual volumetric strain as well as residual shear strain,and the discreteness was very small.In contrast,the relationship between Cdr/S21 and the dynamic strain amplitude had a relatively large discreteness.From the test results,we derived the fundamental Shen Zhujiang model parameters for analyzing seismic subsidence.The results may provide a foundation for the deformation analysis of subsidence at Dalian Airport.They may also guide industrial park land reclamation engineering and seismic design on earthquake prone ground,and are applicable to similar engineering designs.

    • Mechanism of Changes in Microstructure of CompactedLoess Based on Triaxial Test

      2014, 36(1):753-758.

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      Abstract:Loess is widely distributed in China, and it’s an example of regional soil with uncommon characteristics.Because of its special formation process and environmental conditions,loess has unique structural characteristics,which are closely related to its physical and mechanical properties.Studying the microstructure of loess can speak to its possible uses in macroscopic engineering and explain the essential factors of its deformation and strength.At present,the study of the quantitative parameters of the microscopic structure of soils has achieved many results.These results provide a convenient method for the quantitative analysis of how the microstructure of loess changes under triaxial shear tests, which can provide a more reliable basis for the interpretation and validation of macroscopic test results.The macroscopic tests are unconsolidated and undrained triaxial shear tests.The confining pressures for the samples are 100,200, and 300 kPa,and the shear rate of all samples is 0.8 mm/min. Performing macroscopic tests to simulate the actual projected path of building loads allows shear strength parameters to be obtained.The samples for the microstructure test are taken after macroscopic triaxial shear test,with a sample size of 3.91 cm (diameter) × 8 cm (height).All samples are sliced from the major principal stress direction,which is the vertical plane, as well as the horizontal plane,and the cut positions are in the center of the specimens.A JSM-6610LV scanning electron microscope (SEM) from Qinghai University was used to observe samples.During the scanning,2~3 areas of each sample were selected to take photographs.The magnification of all samples was 150 times.Quantitative analysis of the changes in the microstructure of loess was then made by reviewing the SEM images.The SEM was used to observe the microstructure of the compacted loess in the horizontal and vertical planes before and after shearing under triaxial shear tests,and the observed planes are 8.This paper analyzes the microscopic nature of soil strength in three respects:the changing characteristics of pore arrangement,pore patterns, and pore scale.Test results reveal that the probable entropy is near 1 before and after shearing and the pore arrangement is disordered at different confining pressures after shearing,which minimally influences the macroscopic strength.The average shape factor and fractal dimension of the pore morphology at different confining pressures show a decreasing trend after shearing,and the changing characteristics of the pore pattern contribute significantly to the strength of the compacted loess.The aggregate level of soil particles is positively related to the strength of the soil samples.Increases or decreases in the void ratio result in the opposite changes in strength,and the changes in pore scale are the control factor of strength.Changes in the microstructure before and after shearing could be explained by macroscopic experimental phenomena.

    • Visualization System of Immersed Tube Tunnel Construction Basedon Remote Real-time Monitoring

      2014, 36(1):759-764.

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      Abstract:In the process of immersed tube tunnel construction,floating and sinking are among the main priorities carried out underwater.The current construction technology cannot adequately or accurately control the floating and sinking processes,because the construction is carried out underwater.The result of this is the work must be done by hand.The visualization system of immersed tube tunnel construction based on remote real time monitoring is helpful in assisting with the measurements in construction sites and checking the results of diving operations for the distance of abutting points.This makes this visualization system greatly significant and useful in maintaining the safety and management of the construction in the immersed tube tunnel.The construction is unique because of its floating and sinking processes.In this paper,a series of key technologies are employed and integrated,including the establishment of the measuring point coordinate system making use of GPS and accurately converting coordinates,the use of the PSM configuration,visualization technology based on VTK,Autodesk 3DS Studio MAX,model driven data,Microsoft SQL Server Express,and others.A three dimensional visualization system of immersed tube tunnel construction based on remote real time monitoring is designed and developed by combining these key technologies.The system includes a GPS testing system in the pipe section and a dip angle system in the construction site for the processes of floating and sinking.The database of Microsoft SQL Server Express is included in the control center,along with the SOAP Web Service protocol communication.More specifically, the system can display the real time situation of a section of pipe on the construction site, inquire about a great deal of information concerning the pipe section,and play back any time sequence of the construction process.The presented visualization system realizes the function of remote real time monitoring for the tube’s floating and sinking,and it is successfully applied to the construction of the Haihe River immersed tube tunnel engineering in Tianjin.Its results closely match the information from the construction technical personnel and can reflect the pipe section’s real time situation and tendency in the toleration of the engineering error range. In addition,the system provides a guarantee for the safety and efficiency of the construction and can be further applied to related engineering projects.

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