• Volume 35,Issue 1,2013 Table of Contents
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    • Study on Method for Preliminary and Detailed Evaluation  on Liquefaction of Loess Sites

      2013, 35(1):1-8.

      Abstract (952) HTML (0) PDF 792.27 K (1101) Comment (0) Favorites

      Abstract:Loess liquefaction is a disastrous phenomenon which should be carefully treated to reduce the risk. But the relative lacking of both site study results and engineering experience makes it difficult to evaluate liquefaction potential of loess of construction sites. Through many studies carried out since 1990's, the understanding for loess liquefaction is improved substantially. As a result, to incorporate of these studies in seismic code became urgent, but at the same time, new proposals on loess liquefaction often face scrutiny from engineers. In order to resolve the difference between laboratory studies and information obtained from field, the two approaches must be combined and any proposal on evaluation of loess liquefaction should at least sound reasonable by applying field test data, which is the backbone for geotechnical analysis. Based on previous studies, this study carried out experiment in laboratory to get understanding of loess liquefaction behavior and the main factors that determined whether the loess sample wound liquefy or not. Then using feedbacks from engineers on accept method for loess liquefaction evaluation, field data of saturated loess site were collected, and the liquefaction evaluation method recommended in Chi- nese "Code for seismic design of buildings" ( GBS0011 -- 2010 ) ( referred as "national seismic code" } was examined to validate its suitability for loess liquefaction. Through all these efforts, it is found that the liquefaction of loess cannot be properly evaluated by using the current liquefaction potential evaluation method in national seismic code. And the laboratory test is good at providing preliminary evaluation information on weather loess will liquefy or not under certain seismic in- tensity. For detailed evaluation of loess liquefaction, field data interpretation is more reliable. Based on these understandings, the proposed method on loess liquefaction is a two stage evalua- tion: 1) for Preliminary evaluation of loess liquefaction, the age, clay content, shear velocity, plastic index, degree of saturation should be used to determine weather loess; 2) For detailed e- valuation of loess liquefaction, the principles behind the Chinese code for seismic design of build- ings are still valid, but the criteria should be modified to reflect the actual field test data from sat- urated loess site. It is recommended that SPT reference values or NO, as it represented in national seismic code should be reduced and a set of more realistic values which are respectively for design ground motion0.1 g, 0.15g, 0.2g, 0.3gand0.4gshouldbe7, 8, 9, lland13. This proposal is accepted by expert during the drafting of "Specification for seismic design of building" of Gansu province (DB62/T25- 3055- 2011), which is a milestone for liquefaction evaluation of loess sites.

    • Evaluation of Seismic Earth Pressure Considering Lateral Deformation

      2013, 35(1):9-20.

      Abstract (842) HTML (0) PDF 757.00 K (1293) Comment (0) Favorites

      Abstract:Evaluation of seismic earth pressure is one of the key items in the earthquake-resistant design of retaining structures.Previous studies indicate that seismic earth pressure is closely related to the lateral deformation of the backfill.Classic Mononobe-Okabe earth pressure theories can be used to compute the earth pressure at the active and passive limit states only,ignoring the effect of lateral deformation on earth pressure change.In this paper,the variation of earth pressure coefficient with the strain increment ratio is investigated.The earth pressure coefficient is experimentally confirmed to have no unique relationship with the wall displacement,but it has a unique one with the strain increment ratio.The compression-dilatancy coupling effect is found to be responsible for the dependency of the earth pressure change on the strain increment ratio and also the lateral strain constraint of the backfill.From this finding and new concept of intermediate soil wedge,a new method is then developed for the evaluation of the seismic earth pressure under any lateral deformation.Furthermore,Its essential effectiveness is preliminarily checked through comparing the calculated results with model test data.

    • Pushover Analysis Method of Underground Structures under Reversal load and Its Application in Seismic Damage Analysis

      2013, 35(1):21-28.

      Abstract (1018) HTML (0) PDF 515.30 K (1445) Comment (0) Favorites

      Abstract:Although response history analysis is the most rigorous procedure to compute seismic demand,pushover analysis is more common in practice with its advantage of conceptual simplicity and computational attractiveness.A pushover analysis procedure with monotonically increasing effective earthquake forces following an invariant depth-wise distribution is introduced in the paper.Considering the reversal directions of seismic load,which is not included in the traditional pushover analysis with monotonically increasing forces in one direction,a cyclic reversal loading pattern is proposed in this paper.With the algorithm based on multiple point constraints,the implementation procedure,basic functions and special features of pushover analysis with cyclic reversal loading are introduced in detail.In the proposed procedure,the analysis model is imposed with the effective earthquake forces in the positive direction and unloaded when the target displacement is reached.Then the model is imposed with the reversed forces and unloaded when the opposite target displacement is reached.With the proposed procedure,we can estimate the structural capacity during earthquake more reasonably by considering the double direction stress of the underground structures.Subsequently,a damage model based on the pushover analysis with the cyclic reversal loading pattern is proposed by approximately viewing one cycle of reversal load as an earthquake event.With the proposed model,the complicated analysis of dynamic soil-structure system can be avoid and the damage assessment of underground structures can be conducted with the structural stiffness before and after one reversal load pushover analysis.Finally,the validity of the reversal load pushover analysis procedure and seismic damage analysis model are verified by the case study of the Chongwenmen subway station in Beijing.The research in this paper shows that the proposed pushover analysis procedure with cyclic reversal loading pattern can be effectively applied to seismic analysis and damage assessment of underground structures.

    • Preliminary Analysis on Deformation of Reinforced Concrete Beam of Isolation Layer during Construction Process

      2013, 35(1):29-34,41.

      Abstract (827) HTML (0) PDF 418.49 K (933) Comment (0) Favorites

      Abstract:This paper simulated the construction process of isolated and traditional seismic-resistant structures.The internal force and deformation law of the girder in the isolation layers were analyzed in the two types of structures during construction.In addition,the reason for girder cracking in the isolation layers was examined by using the finite element method(FEM) to simulate cracking.The results show that girder cracking in the isolation layers is caused by construction loads,temperature fluctuation,and concrete shrinkage.During the period of construction,structural stiffness develops,which causes adverse reactions of shore deformation,temperature fluctuation,and concrete shrinkage to produce negative effects on long-term performance and durability of the structure.Such factors significantly affect both isolated and traditional seismic resistant structures.Compared with the traditional seismic resistant structure,the isolated structure,which has larger load effects,is more likely to encounter safety issues during the construction period.Each floor's internal forces reach the maximum when the templates of the floor beam are removed and concrete is poured on the structure.The isolation layers are the weakest parts and should therefore be given sufficient attention.

    • Dynamic Tests on the Cement-improved Loess under the Vibratory Load

      2013, 35(1):35-41.

      Abstract (842) HTML (0) PDF 482.08 K (877) Comment (0) Favorites

      Abstract:In this paper dynamic triaxial tests were performed to explore the order and contribution rate of experiment factors such as depth,cement commingle ratio,compacting factor,water-dipping conditions,and vibration frequency on the dynamic characteristics of cement-improved loess including dynamic deformation,dynamic elastic modulus,and damping ratio.On the basis of the foundation construction of the Datong-Xi'an high-speed railway,a large number of test samples have been obtained that include typical loess profiles of various geomorphic units.The dynamic parameters of cement-improved loess were tested on the GDS advanced dynamic triaxial test system at the State Key Laboratory of Continental Dynamics.The orthogonal test method was applied to optimize testing.The dynamic load was calculated according to the train vibration attenuation rule of various depths.Loess samples of various cement ratios were created through compaction tests.The dynamic characteristics of cement-improved loess such as dynamic deformation,dynamic elastic modulus,and damping ratio were determined from dynamic tests that included lengthy periods and a large number of cycles.The results showed that within the test factor level range,the primary and secondary order of factors that affected the vibrated subsidence were cement ratio water-dipping conditions vibration frequency depth compacting factor.In addition,cement ratio and water-dipping conditions showed significant influence on dynamic deformation.The primary and secondary order of factors that affected the dynamic elastic modulus were depth water-dipping conditions cement ratio vibration frequency compacting factor.In addition,depth and submerged conditions showed significant influence.The primary and secondary order of factors that affected the damping ratio were submerged condition situation cement ratio vibration frequency compacting factor depth.In addition,cement ratio and submerged conditions showed highly significant influence.Therefore,an increase in cement ratio results in a significant improvement in the dynamic characteristics of cement-improved loess;no optimal ratio of cement was noted.

    • Seismic Hazard Prevention and Retrofitting of Soil Relics

      2013, 35(1):42-50.

      Abstract (915) HTML (0) PDF 1.43 M (856) Comment (0) Favorites

      Abstract:Soil relics are historical structures built with soil,which have significant historic,artistic,and scientific value.The soil properties and technological innovations are associated and determine which soil relics are vulnerable to nature and human activities.Soil relics are in dire need of protection and seismic safety is of great importance.This paper surveys and evaluates typical soil relics along the silk road in China according to the damage caused by wind erosion,surface weathering,rain erosion,cracking or collapse,foundation settlement,biological erosion,and human activities.The importance of a comprehensive seismic hazard reduction approach for soil relics is emphasized and strategies for hazard prevention,emergency management,and rehabilitation methods for the preservation of soil relics are proposed.Based on the characteristics of the soil relics,the principles for seismic retrofitting,the key retrofitting requirements,and retrofitting design are established.The research results will serve as guidelines for the reduction of seismic risk for soil relics.

    • Dynamic Response Analysis of Irregular Story Isolation Structures under Near-field Earthquake Conditions

      2013, 35(1):51-55.

      Abstract (855) HTML (0) PDF 322.27 K (1130) Comment (0) Favorites

      Abstract:As a new form of isolation,the story isolation structure not only can reduce the dynamic response of upper structures but also can make up for the deficiency of foundation isolation structures.The existing literature mostly analyzes the regulated story isolation structures in far-field earthquakes.In this paper,an eight-story house with a podium-reinforced concrete frame story isolation structure,a foundation isolation structure,and a seismic structure are simulated by using SAP2000.The dynamic responses of the three structures in near-field earthquake conditions are compared.The results show that the whiplash effect is different in the top stories of the three structures in the near-field conditions.However,compared with the seismic structure,the other two kinds of isolated structures show very good damping behavior.In addition,the damping properties of the foundation isolation structure are better than the story isolation structure.Therefore,structures with a podium should be strengthened at the top of the podium.

    • Elastic-plastic Seismic Response Analysis of Hollow Thin-walled High-pier Large-span T-Shaped Rigid Frame Bridge under High-Level Earthquake Conditions

      2013, 35(1):56-61.

      Abstract (765) HTML (0) PDF 384.00 K (875) Comment (0) Favorites

      Abstract:By using structure analysis software,a finite element model of a hollow thin-walled high-pier and large-span T-shape rigid frame bridge is built for seismic analysis.The elastic-plastic seismic response is calculated by using the nonlinear dynamic time-history response method for high-level earthquakes in high-intensity seismic regions.The results are compared by using the linear time-history and response-spectrum methods.The seismic ductility performance of the hollow thin-walled high-pier structure is also analyzed and evaluated.It is concluded that the hollow high-pier thin-walled T-shaped rigid frame railway bridge is in weak nonlinear state under high-level earthquake conditions;however,the damage is small,as it has good seismic-resistant capability.Compared with the elastic seismic response,the seismic forces experienced by the structure are significantly reduced in the nonlinear plastic response.

    • Dynamic Response of Soil Slope under Near-fault Gound Motions

      2013, 35(1):62-68,90.

      Abstract (1176) HTML (0) PDF 773.23 K (1215) Comment (0) Favorites

      Abstract:On the basis of the distribution characteristics of landslides along the fault in the Wenchuan earthquake,the finite difference FLAC program was applied to analyze the dynamic response of the soil slope by using the nonlinear time-history method.Near-fault ground motions with the forward directivity effect,fling-step effect,and non-pulse were selected as seismic inputs.The results show that the potential damages to slopes caused by pulse-like ground motions are significantly greater than the cases with non-pulse ground motions,and the dynamic responses of slopes caused by fling-step pulses are slightly larger than those associated with forward directivity pulses.An amplification effect of the peak horizontal acceleration is apparent in the vertical direction of slope,and the amplification coefficient increases under forward directivity pulses and decreases under flin-step pulses.Furthermore,the peak horizontal acceleration at the bottom of slope induced by fling-step ground motions is larger than that of forward directivity or non-pulse ground motions.

    • Simplified Method for Evaluating Seismic Performance of Pile Foundation

      2013, 35(1):69-83.

      Abstract (762) HTML (0) PDF 901.71 K (1164) Comment (0) Favorites

      Abstract:Performance based design for pile foundations can be analyzed on bearing capacities and deformations.The foundation capacities are often computed knowing the superstructural loads and their combinations.The design needs to consider ordinary and special conditions.Conventional calculation methods or other reliable methods can be adopted.Influence factors are assessed by probability and/or reliability analyses to match the PBD requirements.On the other hand,foundation deformations can be analyzed further.The effects of seismic forces,soil parameters and geological structure could be evaluated independently.This paper introduces the seismic PBD analysis on piles using one-dimensional wave equation analysis and the so called PBEE analysis.A case study is discussed on the bridge pile foundations.The key issues in the analysis are design PGA,accelerogram,pile dimensions and the amount of steel bars in use.It is found that if the soil liquefaction influence could be negligible,then the maximum bending moment would occur at pile head,in which to increase the ductility of the pile at the pile head will help the seismic performance of the piles.

    • Time-domain Method for Free Field in Layered Half Space under P-SV Waves of Oblique Incidence

      2013, 35(1):84-90.

      Abstract (829) HTML (0) PDF 407.95 K (1157) Comment (0) Favorites

      Abstract:A 1D finite element method in time domain has been proposed by Liu and Wang for calculating the in-plane free wave field in elastic layered half space under the plane P and SV waves of oblique incidence(Engineering Mechanics,2007,24(7): 16-22(in Chinese) and Acta Mechanica Sinica,2007,23: 673-680).The viscous artificial boundary condition is used in this method to approximately model the radiation damping of underlying bedrock half space.This leads to the 1D finite element method with low accuracy.An artificial boundary condition is proposed in this paper,which can exactly model the radiation damping of bedrock half space.Due to that the outgoing waves in bedrock are the plane P and SV waves with known propagation directions,using the constitutive relation between stress and displacement in elastic media,the impedance boundary condition between stress and velocity on artificial boundary is developed.The 1D finite element method is further improved by using the new artificial boundary condition to replace the viscous boundary condition.Numerical examples indicate that the improved 1D finite element method has the higher accuracy than the original method,and the solution using the improved method is identical very well with the theoretical solution.

    • Multiaxial Formulation and Numerical Implementation of a Constitutive Model for the Evaluation of Large Liquefaction-induced Deformation

      2013, 35(1):91-97.

      Abstract (1272) HTML (0) PDF 715.02 K (1356) Comment (0) Favorites

      Abstract:Based on the physics of large post-liquefaction deformation of sand and the related elastic-plastic constitutive model suited for two dimensional stress space,mapping rules for plasticity and dilatancy are formulated in three dimensional stress space,and the three dimensional model for the analysis of post-liquefaction deformation of sand is established.According to the features of the model,for the model's numerical implementation into the open-source finite element platform OpenSees,the semi-explicit Cutting Plane algorithm is used as the stress integration scheme,and the Pegasus algorithm is used to locate the stress projection on the bounding surface.Combined with coupled u-p elements,simulations on an undrained cyclic torsional shear test is conducted,and a three dimensional site response analysis is also performed,the simulation and analysis exhibite the model's great capabilities in simulating small to large deformation in the pre-to post-liquefaction regime of sand.

    • Finite Element Simulation of The Structure with Tuned Liquid Damper

      2013, 35(1):98-103.

      Abstract (887) HTML (0) PDF 390.37 K (1014) Comment (0) Favorites

      Abstract:Tuned liquid damper is a passive energy dissipation device.It is very difficult to grasp the true and accurate characteristics of vibration reduction of tuned liquid damper,because of interaction between water and structure,thus it is becoming an important work to establish a more precise water-structure interaction mode,and discuss the seismic performance of the structure with tuned liquid damper.The fluid-structure interaction(FSI) mode of tuned liquid damper system is built with finite element analysis tool ADINA in this paper.Using the ADNIA FSI module,this fluid-structure interaction mode is calculated by Transient Analysis,simulation results is a good agreement with the test results of the simplified model.By Time history analysis,the instantaneous properties of the flow field of tuned liquid damper are obtained,and then based on this instantaneous properties of the flow field,the relationship between seismic performance of the structure with tuned liquid damper and three factors(frequency ratio,ground motion and mass ratio) is analyzed,the comparative analysis results show that frequency ratio is a most significant influencing factor.At last,some design advices of tuned liquid damper are given.

    • Discussion of the Earthquake Force Calculation in Landslide Stability Evaluation

      2013, 35(1):104-108.

      Abstract (713) HTML (0) PDF 345.30 K (935) Comment (0) Favorites

      Abstract:Domestic and foreign currently research and practical application of the landslide stability evaluation theory was described in the paper.Compared the four norms about the earthquake force calculation that the geology and mineral resources industry norms which calculate the seismic forces in the static method is no influence coefficient multiplied by 0.25,which has enormous difference to the other norms,So this provision in the norms is debatable by many examples analysis.Finally,according to the Macro earthquake damage phenomenon the geological situation which cause landslide was put forward and analyzed,the methods and ideas for landslide control engineering design and specification revision were put forward.

    • Combination Method of Wave Functions to Solve the Problem of Scattering in 2D Elastic Half Space

      2013, 35(1):109-113.

      Abstract (896) HTML (0) PDF 258.42 K (1025) Comment (0) Favorites

      Abstract:This paper puts forward a new method which combine the characteristic functions of body waves and surface waves to solve the problem of non-uniform input,which is the displacement of the boundary of the irregular valley topography under the incidence of different kinds of waves in different angles.The method strictly meet the free-surface requirements,and overcome the shortcomings that the existing wave function expansion method cannot express the problem of scattering in two-dimension irregular topography completely.The numerical example shows that the method has the advantages in accuracy,stability,and calculation,which can be applied to the non-uniform input problem of the structure-foundation dynamic interaction.

    • Experimental Analysis of the Acoustic Emission Characteristics of Sandstone Specimens under Uniaxial Loading Tests

      2013, 35(1):114-118.

      Abstract (750) HTML (0) PDF 293.40 K (778) Comment (0) Favorites

      Abstract:Acoustic emission(AE) is a ubiquitous phenomenon associated with deformation and failure of rock material.Experiments on AE characteristics of full-regime sandstone failure are conducted with a stiffness test machine under the condition of uniaxial compression.The relationships of stress characteristics with time-strain level and AE characteristics with time-strain level are obtained in the failure process of sandstone specimens.On the basis these results,the relationship of AE characteristic with strain level is discussed.The approximate critical point of the sandstone specimen is determined to be 0.9 through the curve fitting method.This study provides theoretical guidance to the monitoring and prediction of sandstone behavior.

    • A Study on the Influencing Factors of Joint Rock Slope Stability under Earthquake Activity

      2013, 35(1):119-125.

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      Abstract:Disaster survey results of the Wenchuan earthquake show that seismic landslides mainly develop within thick-bedded or massive rock,in which local intensity is relatively large and joints are obvious.Although seismic landslides differ markedly from those induced by rainfall and other factors,this topic has not drawn sufficient attention.Moreover,numerical analysis methods of finite element and finite difference,both based on the assumption of continuous media and small deformation,are used in previous studies of slope stability.However,some limitations exist in dynamic analysis of large deformations of rock slope due to a large number of interfaces of discontinuity. To overcome those problems,the dynamic response of joint rock slope in this thesis is simulated by means of the discrete element numerical simulation,particularly deformation characteristics,failure mechanism,and influencing factors of slope stability.Here,a rock slope containing two groups of joints is used as the research object.In addition,discrete element numerical simulation is conducted,and actual earthquake records are input to simulate a large number of cases.The influencing factors of the joint rock slope stability are respectively explored under various conditions of slope height,seismic intensity,slope angle,and joint angle.Topographic amplification effects are observed from both acceleration and velocity of the monitoring points of the slope.Joint rock slope stability is reduced with slope height,slope angle,and seismic intensity.In addition,the stability of the rock slope that contains two groups of joints is complex and is influenced by other factors including joint inclination,slope angle,the tendency of joints,and the angle between two group joints.The regions of tension failure are gradually extended to the shear zone and eventually lead to slope instability and failure,compounded by tensile and shear failure.This study provides a reference for evaluation of the rock slope and joints stability under seismic loading in mountainous areas.

    • Seismic Response Analysis of Valley Topography

      2013, 35(1):126-132202.

      Abstract (829) HTML (0) PDF 770.16 K (914) Comment (0) Favorites

      Abstract:The earthquake damage phenomenon indicates that the distribution of earthquake ground motion differs significantly in various parts of bedrock valley areas.The amplitude of ground motion has an important direct impact on the extent of the seismic hazard;larger amplitudes result in more severe disasters.Many towns located in the valley areas are widely distributed over Shanxi,Gansu,and Sichuan provinces and sustain severe damages from earthquakes.Research on this type of area has recently increased with particular emphasis on valley terrain.Many scholars have reported that input data is a significant problem for calculating the parameters of ground motion during strong shocks in such cities because microzoning is often closely related to the characteristics of soil strata and the geomorphological conditions.Nevertheless,the conditions of terrain and geology are interdependent with each other and have an impact on ground motion;it is widely accepted that terrain has an important effect on ground motion.Common valley terrain can be divided into three categories including V valley,inverted trapezoidal valley,and trapezoidal valley.V valley and inverted trapezoidal valley are widespread and are the topics of numerous studies.The bottom of V valley is narrow,and many geological disasters such as rockfalls occur in trapezoidal valleys.The inverted trapezoidal valley is more suitable for residency;therefore,research on this type of valley terrain is important.Because the drainage systems and valley landforms are generally not symmetric,homogeneous terrain models with various slope angles,depth-to-width ratios,and asymmetry of valley are used to analyze the variation of peak ground acceleration(PGA) in valley areas.By comparing the PGA,seismic spectra,and acceleration time history,the relationship between ground motion and topography is analyzed in this study.The results show that 1) the ground motion amplitude at the valley bottom appears to reach maximum value when the slope angles are approximately 40°~50° and later decreases.The minimum is achieved when the angle is changed from 65° to 80° on the basis of spectrum ratio.These results are consistent with published results on the Wenchuan earthquake.The wave in the high-pitched slope valley decays slowly,which it could be due to diffraction of P,SV,and Rayleigh waves.2) No obvious variation of PGA on various valley areas is observed when using a small depth-to-width ratio model,regardless of high-frequency and low-frequency impulse input.With an increase in depth-to-width ratio,an input of high-frequency impulse causes significant variation,and the PGA in the valley center is larger than that at the valley bottom.Diffraction of P,SV,and Rayleigh waves is higher with an increase of depth-to-width ratio,and the distribution of PGA is complex.In addition,the orographic effect is stronger when the wavelength was close to the width of the bottom of valley and slope.3) The amplification factor of earthquake ground motion increases with slope angle and slope height.In addition,the valley asymmetry has an influence on the PGA at the valley bottom.The maximal PGA at the valley bottom is often close to the lower slope side,and the smaller PGA appears to correspond to the side with the larger slope angle;the amplification factors of both sides is increased due to free face changing with the increase in slope angle and slope height.4) Ground motion is consistently amplified on or near the top of the hill areas compared with that at the bases.The protruding topography has amplification effect on ground motion while the hillside has a constrained effect.In addition,a larger slope angle and height relates to more severe damages to residential areas;the effect is less intense with distance from mountains.The amplification factor of the valley between two mountains is related to the distance of the two mountains.If the distance is shorter,the factor is smaller.

    • Analysis and Numerical Calculations of Stability on Ancient City Wall under Various Sapping Depths

      2013, 35(1):133-138.

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      Abstract:The width of the top of the ancient city wall in Liangzhu,which is known as the first city in China,reaches 40~60 m;stability issues for this wall have been identified.Finite differences determined through FLAC3D software were considered to build a calculation model for examining failure laws and the mechanism of the ancient city wall under various sapping depths.The results show that when the sapping depth is not sufficiently large,the entire city wall is stable,and local plastic failure occurs near the sapping location.When the depth of sapping increases,the plastic failure area becomes wider and deeper and can reach the top of the wall.In addition,the soil displacement increases until the entire wall slides.The sapping contributes to the damage of the wall,a potential slide opening appears in the sapping area,and a plastic area appears in the wall,which leads to sliding of the entire wall.

    • Shallow Seismic Prospecting Data Acquisition and Processing Technology of Crooked-line Measurement

      2013, 35(1):139-144.

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      Abstract:In the collection of shallow seismic prospecting data,limitations of local geological conditions prevent measurements along a straight line.To obtain high-quality seismic data,crooked-line seismic exploration can avoid obstacles and adapt to local geological conditions for shotpoint and receiver.However,due to the dispersion of offset,which influences the superposition of common reflection bin gathers and the authenticity of seismic profiles,and the shallow seismic data,acquisition and processing technology are ineffective in the crooked-line method.Therefore,it is necessary to control the quality in crooked-line seismic data acquisition and processing. During crooked-line data collection,the discrete common midpoint should be controlled within the allowable range to meet the condition of common reflection bin stacking in time and space.At some areas of large curvature,the common midpoints exceeding the range of discrete conditions should be eliminated,and the selective superposition should maintain the concurrency of each stack gathers in common bins. In the processing of shallow seismic prospecting data,the number of receivers is fewer,and the fold of data is lower than the petroleum seismic data.Therefore,time and space stack conditions of common reflection bins should be fully considered prior to the processing of shallow seismic prospecting data.Compared with regular straight-line seismic prospecting data processing,crooked-line seismic data processing is essentially the same in processing methods,processes,and parameter selection.The most fundamental difference is superposition.Crooked-line seismic data processing includes a common reflection bin stack in which several neighboring reflection points add up as a common reflection bin,while the straight-line is a common reflection point(CRP) stack.For this reason,the crooked-line's common reflection bins gathers are not strictly common reflection point gathers.Larger common reflection bins include more CRP participation in the stack,and the signal-to-noise ratio is high.Due to the average effect,however,a greater number of CRPs involved in the bin superposition results in lower resolution.Therefore,according to the geometric definition of the crooked-line method,crucial steps include selection of the common bin centerline and the common reflection bin grid during data processing in addition to and balancing the relationship between resolution and signal-to-noise ratio. By using a line measured in the Longnan mountainous area of Gansu province as an example,combined with the superposition of crooked-line common reflection bins in time and space conditions,this paper mainly analyzes the methods of control offset point dispersion range in acquisition and processing.A true and high-quality seismic section was obtained with processing by PROMAX software that showed improvement in effective wave energy,continued clarity in the events of targeted layers,suppression in all types of interference waves.These results prove that the shallow crooked-line seismic prospecting method is feasible and effective in theory and actual usage.

    • New evidence for Late Quaternary Activity in the Middle Segment of the Northern Margin Fault of Maxian Shan in Lanzhou

      2013, 35(1):145-153.

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      Abstract:In the southern mountainous region of Lanzhou city,there are four large-scale regional active fault zones of late Quaternary.These are the northern margin fault of Maxian Shan("Shan" means Mountain)(F1),the southern margin fault of Maxian Shan(F2),the southern margin fault of Xinglong Shan(F3),and the northern margin fault of Xinglong Shan(F4).They make up the Maxian Shan-Xinglong Shan active fault system.The northern margin fault of Maxian Shan is the longest among them.The fault's eastern end begins in Neiguanying,moves along Miaowan,Yangzhai,and Yinshan,then meets with the southern margin fault of Xinglong Shan in Moyunguan of Qidaoliang and continues along Tianjiagou,Hutan,Guanshan,Xianshuigou,and the western part ends in Bapanxia,Yellow River.The fault strike direction is about N60 °W and the total fault length is about 115 km. The geometrical features of the northern margin fault of Maxian Shan are simple.The fault is divided into four segments according to the fault displacement,fault bending,fault step,and differences in recent activity.The secondary faults are the Neiguanying segment(F1-1),the Maxian Shan segment(F1-2),the Qidaoliang segment(F1-3),and the Wusu Shan segment(F1-4).Field investigations indicate that the northern margin fault of Maxian Shan is a seismic fault zone characterized by segmentation.Its eastern segment,the Neiguanying secondary fault,is a late Pleistocene fault.The west segment,the Wusushan secondary fault,is active in the Holocene and produced the Lanzhou M7 earthquake.However,there is no geological and dating evidence for the recent activity of the middle segments,that is,the Maxian Shan and Qidaoliang secondary faults.Nonetheless,in recent years,field investigations have indicated that the middle segments were active during the late Pleistocene and early Holocene,on the basis of left-lateral strike-slip and dip-slip features. According to historical data in the Lanzhou area,several moderate to strong earthquakes with magnitude of about 5~6 occurred in the Maxian Shan area in 1524,1629,and 1901 A.D.besides the Lanzhou M7 earthquake in 1125 A.D.and Yongjing M6.5 earthquake in 1590 A.D.These earthquakes may have correlated with the activity of the northern margin fault of Maxian Shan. The northern margin fault of Maxian Shan was active in late Quaternary and produced several moderate to strong or even large historical earthquakes;therefore,this fault is active and has the potential to produce earthquakes in future.

    • Numerical Simulation of Seismic Tsunami Dissemination at the Continental Shelf of the East China Sea

      2013, 35(1):154-159.

      Abstract (1120) HTML (0) PDF 700.15 K (1052) Comment (0) Favorites

      Abstract:The seismogenic tsunami is a type of sea wave directly caused by uplifting and subsiding of the ocean floor.It generally has substantial destructive power and can create severe damages to lives.Tsunami studies are important in the field of disaster prevention,particularly in tsunami discrimination and sea-quake disaster evaluation. Chinese scholars conducted studies in this field mainly after the 2004 Indonesia tsunami.In the South China Sea,the huge possibility of seismic tsunami occurrence has become a significant issue.The coastal area of East China Sea is the most economically developed and densely populated region of the country;a tsunami occurrence in this area would be catastrophic.No numerical simulation for tsunamis has been conducted for the East China Sea;therefore,research on the characteristics of potential tsunamis in this area is crucial for tsunami identification and disaster assessment. Such tsunami research for the East China Sea region is the focus of this paper.The geological background of seismic activity history,spatial-temporal tsunami distribution characteristics,potential source area of Okinawa Trough,and occurrence possibility of earthquakes and tsunamis in the East China Sea formed the basis for discussion,in addition to identification and scope of potential tsunamis. By using numerical simulation methods,we assumed five focal points in the Okinawa Trough,and we set six seismic tsunami experience parameters for 6.0-9.0 magnitude as the initial conditions.We thoroughly examined 30 earthquake examples that could generate tsunamis,analyzed the tsunami dissemination process in the East China Sea,and discussed the possibility of a tsunami disaster in the coastal areas of Shanghai in detail. The results show that at different source points with the same magnitude,the initial tsunami wave height is same;thus,the earthquakes with magnitudes less than 8.0 had a negligible effect on Shanghai.For those with magnitude 8.0,only the source point at the northernmost region of Okinawa Trough had an obviously impact.Almost all of the earthquakes with magnitudes of 8.5 and 9.0 had a significant influence on the coastal areas of Shanghai,with the largest potential wave height reaching 3.9 m. The analysis results were and combined with water level changes recorded by a tsunami instrument to estimate the tsunami disaster occurrence potential.Because tide is a major factor in daily water level changes,we predicted the tide at the monitoring points with the numerical simulation methods.The results strongly correlated with the observation data.We considered the water level changes at the monitoring points caused by the Okinawa Trough magnitude 8.5 earthquake occurring at the northernmost point and the tidal prediction results of the entire day to determine the post-shock theoretical value of the water level at various times. The results show that the East China Sea is highly susceptible to a seismic tsunami,the Okinawa Trough is a potential risk source area for Shanghai,and the influence from northern section of the trough is greater than that from the southern section.

    • The Tectonic Stress Field in Southeastern Area of Gansu Province Deduced from P Wave Polarity Data

      2013, 35(1):160-165.

      Abstract (806) HTML (0) PDF 1016.27 K (928) Comment (0) Favorites

      Abstract:To determine the crustal stress field based on the basis of earthquake waves,we analyze data from fixed seismic stations in Gansu and surrounding provinces and the broadband portable seismic array in southeast Gansu province,where three blocks converge to create complex tectonic conditions.Two methods used to directly obtain such stress fields include those based on focal mechanism data and p-wave first motion data.In order effectively use small and microscale earthquake data,the latter method is used in our study.On the basis of near earthquake observation data recorded from November 1,2010,to November 30,2011,we use Zhang's Method to relocate earthquakes occurring in this area.As a result,2 379 earthquakes and 12 129 p-wave polarity data are obtained through which the directions of principal stress axes are inferred.The inversion method and program are provided by Wan.Our study assumes a relative stress value of 0.5.We calculate only the 2-D stress field because most earthquakes have occurred in the research area at depths of 5~20 km;the average depth of 12 km was chosen as the calculating depth.The direction of tectonic stress field in a 0.25° × 0.25° grid in this area is presented for the first time.The orientation of P,B,and T axis azimuths are obtained by 1° × 1° × 1° grid searching.We treat these azimuths as stress flied directions when the contradictory ratio is the smallest.Results show that the maximum compressive stress axis strikes are presented in a radiated pattern;that is,they strike east-west from NEE in northern part to SEE in the east.These findings are similar to that reported in previous research,through which we can infer that the Qinghai-Tibet plateau moving to the northeast encountered the stable Ordos block and the South China block moving to the southeast;thus,the material moved southeast.The earthquakes occurring in this region were fewer and smaller than those west of 104° E;therefore,the stress field inversion result is primarily obtained from smoothing the results of surrounding areas.However,further analysis is necessary to explain why the principal compressive stress axes are steeper here;such research will be the focus of our next investigation.Maximum principal compressive stress axes are steep on the southwestern margin of the Ordos block likely because the material moved east along the West Qinling fault;therefore,the stress environment is tensional.Because the broadband portable seismic array in the southeast area of Gansu province covers density,the constraint mechanism and inversion results are reliable.Detailed characteristics and a relatively reliable direction of the tectonic stress field in southeast Gansu province are obtained in this research.We expect that our results are significant to geological background explanation and earthquake prediction research.

    • Distribution Characteristics of Wavelet Relative Energy on Near-earthquake Wave

      2013, 35(1):166-170.

      Abstract (881) HTML (0) PDF 267.42 K (997) Comment (0) Favorites

      Abstract:Seismic waves have characteristics of non-stationary signals,and their energy distribution is in a finite frequency band.In addition,they contain a significant amount of information about sources and media.Analysis of seismic signals is used to determine the sources and propagation medium and for further study of earthquake mechanisms.Fourier transform is a classic method used for signal processing.Because it is a pure frequency domain analysis method,its shortcoming is lost time information.The Fourier transform method stringently requires that the system is linear and that the signal is stationary.Therefore,high limitations are placed on non-stationary signals.For short-time Fourier transform,constraints of the window function result in difficulties in simultaneously obtaining good resolution in time and frequency domain.Because the wavelet transform has the characteristic of multi-resolution,the time and frequency windows can be dynamically adjusted as the signals changes;thus,the characteristics of local information expression capability is improved in the time and frequency domain.Therefore,the dynamic characteristics of the seismic waves in the frequency and time domain should be determined by the multi-resolution decomposition of seismic signals.In this paper,the multiresolution decomposition of discrete wavelet transform is used to show decomposition of a synthetic waveform that is rebuilt by different level signals of decomposition.The standard square error is 1.554 2e-019,and the root mean square error is 7.351 2e-012 between original and rebuilt signals.The signal is not distorted due to decomposition and reconstruction processing.These results satisfy the requirements of computational analysis.Moreover,nine earthquakes records obtained from the Gansu Seismic Network with a magnitude range of ML3.3-4.2 were processed by using the same methods. Results indicate a relative energy distribution range of 1-15 Hz and an energy peak of 3-6 Hz for the local seismic wave(Δ300 km).For one earthquake,the relative energy distribution of the earthquake differs among stations,which is caused by the focal radiation pattern and medium differences.The statistical test results show that the error level and results of synthetic waveform testing are consistent.This method can accurately determine near seismic energy distribution in the frequency domain characteristics,which is conducive to the study of seismic wave variation in various frequency bands.Moreover,statistical results show that this method is effective and reliable for obtaining details of seismic wave variation.However,it is difficult to explain the phenomenon such that the frequency of the peak energy changes from low to high with an increase in epicenter distance.Therefore,this topic requires further study.In addition,it should be noted that if such a method is used to process data for wavelet window length,some energy may be lost in the calculation process.The results of this study provide reference value in the research of earthquake sources,radiation patterns and seismic wave propagation in an anisotropic medium,and aseismic design for engineering applications.

    • Thermal Infrared Anomaly Prior to Yiliang of Yunnan MS5.7 Earthquake

      2013, 35(1):171-176.

      Abstract (777) HTML (0) PDF 671.82 K (847) Comment (0) Favorites

      Abstract:This study examines the thermal infrared anomaly occurring prior to the September 7,2012,MS5.7 earthquake in Yunnan Yiliang by analyzing infrared remote sensing brightness temperature data recorded by China Geostationary Meteorological satellite FY-2C/E.Infrared data of the prime time from 1:00 to 5:00 local Peking time was selected as the data source.Through data processing in which cloud data was disregarded,the power spectrum transform method was used to analyze and research the temporal evolution diagram of the earthquake thermal infrared anomalies and the timing curve of the brightness temperature average.The results show that 90 days prior to the earthquake,in approximately July 2012,a significant thermal anomaly area occurred near the epicenter,and exhibited irregular shapes.With the passage of time,the abnormal range gradually expanded along a particular direction of tectonic stress field,rapidly mutated,and gradually migrated from north to south.A large range of infrared anomaly up to hundreds of kilometers in length was recorded in the epicentral area,which is inconsistent with the temperature trend observed in the seismogenic zone.This abnormal area reached the maximum on September 1,2012,and gradually shrank after the earthquake occurred.The anomaly amplitude was rapidly reduced in the area near the seismogenic fault before disappearing.The earthquake thermal anomaly cycle was 64 days,and the thermal anomaly duration was more than 30 days.Prior to the earthquake,the magnitude of relative change was more than 10 times,for a maximum of the previous five years.From mid-July 2012 to the seismogenic day,the average increased sharply,and abnormal peaks appeared during the four days prior to the earthquake.After the earthquake occurrence,the characteristic amplitude gradually reduced,and anomalies dissipated step by step.Moreover,we determined that the brightness temperature anomaly exhibited zonal distribution along the fault,which should be related to the distribution of active tectonics.The thermal infrared anomalies observed prior to the earthquake were fairly obvious and persistent,lasting through two stages of initial and strengthening warming.The abnormal area shifted,expanded along the fault direction,and rapidly increased.The epicenter of this earthquake was not in the abnormal maximum area but approached the fault near the edge of the anomaly area.This situation is consistent with the results of most earthquake cases and may be related to the geological structure and the underground environment of the epicenter.These characteristics can provide some clues in determining future seismogenic time and tracking the location of the epicenter.Because the current understanding of the genetic mechanism of earthquake thermal infrared anomalies is not yet complete,future research should include shock cases and law summaries.However,the highlights of the thermal infrared anomaly occurring prior to this earthquake presented in this study are indeed authentic.

    • Microearthquake Location Determined by Portable Seismic Array Data in Southeast Gansu Province

      2013, 35(1):177-182.

      Abstract (810) HTML (0) PDF 994.31 K (772) Comment (0) Favorites

      Abstract:In November 2009,a high-density portable seismic array consisting of 150 broadband seismographs was deployed in southeast Gansu province through the cooperation of the Lanzhou Institute of Seismology and the Institute of Geology,CEA.We obtained a large amount of microearthquakes data recorded by this array through November 2011.The data of the portable seismic array and the permanent seismic network is merged and saved in Windows Event Log(EVT) format.On the basis of the amplitude frequency characteristics of seismic waves,we design an automatic identification program of earthquake events,adjust the threshold,and clip the waveforms.We then use EDIAS/MSDP software to re-identify earthquake events,analyze seismic phases,and locate earthquakes by using the simplex location method.The initial localization of 3 243 earthquakes events in the region(32.9°-35.0° N,102.7°-107.1° E) is obtained.Finally,we relocate these earthquakes by using the grid searching algorithm.In this algorithm,the 3-D velocity model is used to obtain theoretical travel times by the ray tracing method.By computing the root mean square(RMS) residuals of theoretical and observational travel times,the corresponding point of the minimum residual is determined as the relocation point.Accurate relocation of 3014 microearthquakes recorded by three or more stations is obtained with this algorithm,which is 1 693 more than that obtained from the permanent seismic network in the same period.We apply the results to seismicity analysis in southeast Gansu province and discuss the relationship between seismicity and active faults.The seismic data recorded on three profiles across several fault zones and the spatial distribution of the faults is analyzed in detail.The results show that the relocated earthquakes are more concentrated on obvious strips or clustered around the faults.Most of these faults have comparatively strong seismicity in southeast Gansu,particularly those concentrated in the Wenxian-Wudu area,which is the transform zone of several groups of faults.However,seismic activity of the Tianshui eastern segment of the West Qinling Northern Frontal fault is relatively weak.The focal depths of the earthquake swarm are mainly distributed in the range of 5~20 km,which proves that the seismogenic layer is in the upper or middle crust in this area at an average of 11 km.As indicated by the focal depth profile,the focal depths are closely related to the faults,and earthquake belts correspond well with faulted structures.The fault zone is composed of the Diebu-Bailongjiang and Guanggaishan-Dieshan southern and northern Piedmont faults within a width of 20 km.The Tazang fault belt and the Lintan-Tanchang fault zone are wider.In depth direction,the earthquakes are obviously compact on strips near the West Qinling Northern Frontal fault,the Wenxian-Kanxian fault zone,and the Chengxian basin Northern and Southern Frontal fault.The seismic activities of these faults extend to the middle crust and upper part of the lower crust.

    • Near-field Acceleration Records and Preliminary Analysis of M_L2.1 Shijingshan District Earthquake on Oct.12,2011,Beijing

      2013, 35(1):183-189.

      Abstract (947) HTML (0) PDF 1.04 M (1031) Comment (0) Favorites

      Abstract:An earthquake with a magnitude(ML) of 2.1 occurred at 16:40 UTC,October 12,2011,in the Shijingshan district in Beijing with an epicenter at 39.95° N,116.16° E.Eleven near-field strong motion stations,located less than 20 km from the epicenter,clearly recorded temporal variation of acceleration during the earthquake.The largest value of peak ground acceleration in the east-west(EW) and north-south(NS) components,22.528 gal and 30.989 gal,respectively,were both recorded by station LSG,which is situated approximately 5.6 km from epicenter.The largest value of peak ground acceleration in the vertical component was 12.797 gal,recorded by station CCS at an epicenter distance of 2.2 km.We synthesized the horizontal component by EW and NS records and used Generic Mapping Tools(GMT) software to mesh and illustrate the influence of horizontal and vertical acceleration on the field contour map.The results show that generally,the value of the NS component is larger than that of the EW component,and the horizontal component is larger than the vertical.Moreover,the acceleration distribution and influence field contour map of the horizontal component shows that peak ground acceleration in the southern area is a low value and that in the northern area is high.In addition,the two regions are divided by a transition zone that strikes near east-west(EW) or NEE.We obtained the average peak ground value of three components at 1 s intervals from station records after the earthquake occurred,which we synthesized into horizontal and vertical components to illustrate temporal variations in the map produced by GMT.After analyzing the average value records and temporal variation map,we detected that the decay in the NS direction is faster than that in the EW direction and that decay is faster in the vertical component than that in the horizontal component.Excepting the near-field strong motion stations,23 Capital Circle broadband digital seismic stations recorded digital waveform data during the earthquake.We interpreted initial P-wave polarity from these records and employed grid-point test method to obtain the Focal Mechanism Solution of the event.Results indicate normal faulting dominant in the Beijing-Tianjin area.The best double couple solution of the event is 295°,39° and-74° for strike,dip and rake angel,respectively;those of the other nodal plane are 96°,53°,and-102° with a 13% inconsistency ratio.By combining these results with the acceleration analysis results,we determined that the strike of the second nodal plane with a larger dip angel is near the EW direction,which is consistent with the strike of acceleration transition zone.In addition,the microepicenter of the event does not coincide with the macroepicenter.These findings indicate that the nodal plane of strike 96°,dip 53°,and rake-102°may coincide with the seismogenic fault.Although the work in this study is a preliminary analysis for acceleration records and seismic digital waveform data,the results can provide a reference for quick determination of earthquake influence field and hazard assessment following a large earthquake and are highly significant for earthquake emergency response and disaster relief.

    • Test Analysis on Geoelectrical Resistivity Observation Combining the Surface and Deep-well Methods at Tianshui Seismic Station in Gansu Province

      2013, 35(1):190-195.

      Abstract (905) HTML (0) PDF 359.85 K (1245) Comment (0) Favorites

      Abstract:In early 2011,Tianshui seismic station of Gansu province developed a special project for observation on deep-well geoelectrical resistivity,which pushed the horizontal geoelectrical observation to stereo observation.The methods include surface horizontal observation,deep-well horizontal observation,and the electrode interchange-able test between surface and deep-well observation.Through continuous observation in past two years,data obtained by two methods which are deep-well M、N observation supplied power by surface A、B and deep-well horizontal observation is relatively stable and reliable.Meanwhile,deep-well M 、N observation supplied power by surface A、B could contribute to reliability analysis on data changes.At observation sites where electromagnetic environment is more complex,deep-well M、N observation supplied power by surface A、B and deep-well horizontal observation may be two effective methods.

    • Research on the Effect of Seismogenic Structure with Complex Spatial Relationship on Earthquake Mechanism with the Wenchuan Earthquake as An Example

      2013, 35(1):196-202.

      Abstract (728) HTML (0) PDF 480.02 K (943) Comment (0) Favorites

      Abstract:The influence of seismogenic structures with complex geometric relationships,in which the seismogenic structure is not parallel in the planar projection,on the mechanism of earthquakes is studied.Seismogenic structures that influence each other have a damping effect on regional earthquakes after their occurrences.However,the mechanical mechanism research shows that when the fault distribution is of complex geometry,the increasing and decreasing effect of earthquakes differ.Perpendicular intersectional faults are known as perpendicular faults;those equivalent to the bottom line are known as bottom faults.If an earthquake has occurred on the bottom fault,the perpendicular fault will have damping effect,which is known as the occurrence of an earthquake on a bottom fault following the occurrence of an earthquake on a perpendicular fault.If a strong earthquake has occurred on the perpendicular fault,a strong earthquake occurring on the bottom fault is known as the occurrence of a smaller earthquake on a perpendicular fault following the occurrence of an earthquake on a bottom fault.When earthquake occurs on a bottom fault,the relation between magnitude M and damping distance R to the perpendicular fault islg R=0.49 MS-1.97(1) where R is the damping distance in kilometers and MS is magnitude.When an earthquake occurs on a perpendicular fault,which is nearly at a right angle with the bottom fault,energy accumulates in the bottom fault.This result is conducive to damping and is more conducive to the accumulation of energy for earthquakes.When the distance between the top and the end parts of a seismogenic fault on a perpendicular fault is approximately 2~3 times the length L of the seismogenic fault on the perpendicular fault,energy may be superimposed on the bottom fault.The relation between length L and magnitude M on the perpendicular fault islog L=0.48M-1.57(2) Using the relationship of the occurrence of a smaller earthquake on a perpendicular fault following the occurrence of an earthquake on a bottom fault,we investigated the influence of the 1933 Diexi M7.5 earthquake and the 1976 MS7.2 earthquake in Songpan and the effect of energy superposition of the Longmen Mountain seismic structure,which later led to the Wenchuan MS 8.0 earthquake. The seismogenic structure of the Diexi and Songpan earthquakes is approximately orthogonal to that of the Wenchuan earthquake.These earthquakes are more conducive to earthquake occurrences than to shock absorption because of the accumulation of energy. In addition,the complexity of the model of earthquakes occurred in Wenchuan was discussed.Some authors determined that the thrust of the Wenchuan earthquake was caused by the Bayan Har block moving southeastward,which squeezed the Longmen Mountain seismogenic structure.We discussed the complexity of mechanical contradiction for this explanation. In this study,according to China Probabilistic Seismic Hazard Analysis(CPSHA) and the complex geometric relationship of seismogenic structures,we demonstrated the manner in which the seismic zone of the potential seismic source distribution function fi,mj,is identified,and we provided an index of intricate for evaluation.

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