• Volume 35,Issue 2,2013 Table of Contents
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    • Research on the Failure Mechanisms of Rock Masses under Level Seismic Loading

      2013, 35(2):203-207.

      Abstract (775) HTML (0) PDF 270.59 K (1084) Comment (0) Favorites

      Abstract:Based on Mohr-Coulomb failure criterion and wave theory,the failure mechanism of rock and soil masses under earthquake loading has been theoretically analyzed,with the calculation process assuming the maximum value of seismic stress and the most unfavorable orientation.It has been found that cohesive force and normal stress are linearly related to vibration velocity when the burial depth is within a certain range.When the burial depth is constant,vibration velocity increases as cohesive force,c,decreases,so with increasing vibration velocity,stresses in the rock mass would transform from the compressive state to the tensile state and continue to increase.When the vibration velocity is constant,the deeper the burial depth of the rock mass,the smaller is the cohesive force;and the shallower the burial depth,the greater is the tensile stress.When the burial depth increases to a certain value,the rock mass begins to vibrate within the elastic limit and no failure can occur.This research can be applied to the assessment of rock mass stability and the forecasting of geological hazards,as rock masses under different burial depths always have different stress states.More specifically,rock masses buried shallowly store only a small amount of strain energy,limiting their destructive potential.Increasing the burial depth correspondingly increases the strain energy;as a result,the rock masses are closer to reaching their limit state and can more easily fail.The evolution of geological bodies shares a similar rule;namely,when a geological body reaches its limit state,a slight perturbation can trigger a geological hazard,whereas if the geological body has not yet approached its limit state,only a sufficiently strong disturbance will induce the geological hazard.

    • An Effectiveness Analysis on Hybrid Control System of Tuned Mass Damper-base Isolation under Near-fault Pulse-like Ground Motion

      2013, 35(2):208-212.

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      Abstract:Near-fault ground motions can cause severe damage to structures because of its high peak accelerations and macrocyclic velocity pulses.In the last two decades,the seismic isolation technique,which was proved to be very effective for the seismic protection of new constructions and the seismic retrofitting of existing ones,had been applied for buildings,bridges,industrial facilities,and structures of historical value as well.As a consequence,design guidelines for seismically isolated structures have been developed in many countries with a high seismic hazard.The insertion of an isolation system at the base of a building structure allows the horizontal seismic loads to be reduced through a decoupling of the structure motion from that of the soil;moreover,the superstructure behaves like a fixed or base isolated structure along the vertical direction,depending on the value,respectively very high or very low,of the ratio between the vertical stiffness of the isolator and the horizontal one.Base isolation technique,taken as an effective method to control structure's vibration that is induced by earthquake ground motions,has been widely accepted,however,only such an approach can not ensure structure's safety under near-fault pulse-like ground motions with high energy in low frequency band,because strong near-fault ground motions are characterized by long-duration horizontal pulses and very large displacements,which can lead to an oversizing of the isolation system and an amplification of the response of a base isolated structure.Specifically,the frequency content of the motion transmitted by the isolators to the superstructure can become critical when the pulse intensity is so strong that the superstructure undergoes plastic deformations.Moreover,the structural response can be amplified due to the long duration of the pulse.To overcome these problems,many authors have proposed a lot of solutions based on different kinds of isolators and dampers.Nevertheless,some problems remain unsettled if additional damping is adopted,because the displacements at the top of the isolators can be substantially reduced,but the contribution of the higher vibration modes of the superstructure increases,if this contribution becomes too large,it can give rise to significant increase in inter-story drifts and floor accelerations,so it is necessary to find more effective vibration control strategies.A pulse model and a stochastic ground motion model are combined to simulate the near-fault ground motions.The simulation of directivity pulse type ground motions through superimposition of modeled directivity pulse on a non-pulse type motion is a possible approach to meet the scarcity of such motions in studying the structural response.Typically,pulse duration or period,pulse amplitude,and the number and phase of half cycles constituting the pulse have been considered as the parameters which are necessary for such a characterization. The structure dynamic responses are solved by using MATLAB under these artificial ground motions.The effectiveness of TMD-Base isolation hybrid control method is studied through the comparisons of response time histories of a base isolated structure with and without TMD.The results show that this hybrid control method is capable of controlling isolation layer's displacement effectively.

    • Design Optimization and Seismic Reliability Analysis of Truss-type River-crossing Pipe Rack

      2013, 35(2):213-219.

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      Abstract:Oil and gas pipeline construction persists throughout China on national and regional levels.Because many barriers are encountered such as rivers,lakes,mountains,canyons,other construction,and unstable strata,access through and across these barriers are important in oil pipeline engineering design.Thus,construction reliability,safety,and economic impact have been studied.In cross projects,truss-type river-crossing pipe rack is a common form of medium-sized cross-projects because it has a simple structure,is light weight,and provides a convenient way to repair pipelines with ample space.The structure design optimization and seismic reliability analysis of truss-type river-crossing pipe racks are related to the overall performance and safe operation of pipeline structures.In this study,two scenarios of rectangular and inverted triangle truss structures were respectively optimized by using ANSYS parameter design language and a design optimization module,and the optimization results were analyzed to determine the most optimal solution.By simulating the structure's earthquake response,seismic performance analysis was conducted,and the structure of anti-seismic reliability was obtained through reliability analysis for optimal structure design.The optimization results show that the height of the truss increases in the optimizationprocess;however,the width is reduced.In addition,the diameter of pole gradually decreases in the process.The total weight of the structure rapidly reduces with rod cross-section reduction;reduction is rapid in the first three optimization cycles and slows from 54tons to 25tons after 10 optimization cycles to maintain a weight of 18.532t.The analysis of internal force and largest structural displacement show that the structures make full use of material mechanics capability and that the appropriate increase in structural height and decrease in structural width are favorable to the structure.Optimization results show that the two types of structure forms show the same change trends in the optimization.The inversion triangle form has a more simple structure,fewer section species,and a more simple connect247979 node construction than those of the rectangle form.Moreover,the inversion triangle form has weight reduction of 36% over the rectangle form;therefore,the cost of material and construction is less,and mechanics capability is more effective.Response spectrum and time history analyses reveal that earthquake activity in the horizontal direction results in stronger activity on the river-crossing pipe rack than that in the vertical direction because the width of the truss decreases in the optimization to increase vertical stiffness.Reliability analysis shows that the reliability of the structure is 99%.Failure probability of the structure maintains the probability permission bound of construction design.Therefore,the entire structure retains the guarantee probability of 99%.That is,the structure is safe and reliable under the earthquake activity and load.

    • Experiments on Slide Response of Museum Cultural Relics under Earthquakes Considering Various Showcase Boundary Conditions

      2013, 35(2):220-225.

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      Abstract:Many museum pieces are of cultural heritage and worthy of protection for their historical and artistic values.Because such relics are usually free-standing,they are easily damaged during earthquakes.For example,the 2008 Wenchuan earthquake in China led to substantial losses of property such that at least 216 museums were affected,and more than 3169 cultural relics were damaged.Slide motion is a typical seismic response mode of museum cultural relics;large slide sizes may cause relics to drop from their display stands and incur damage.Thus,it is important to study slide response of free-standing cultural relics under earthquake conditions and adopt aseismic measures for protection.In previous works,theoretical analyses were mainly used to study the slide responses of free-standing relics.Experimental studies were insufficient,and boundary conditions of showcases were seldom considered.To determine protection measures for movable cultural relics,slide responses of free-standing cultural museum relics under earthquake conditions are studied by considering various showcase boundary conditions.1:1 scale models were created on the basis of actual of a museum showcase sizes.A glass cultural relic was placed in the showcase by free-standing mode.The static friction coefficient between the relic bottom and its base was determined to be μ = 0.15 and the barycenter height values of the showcase and relic were calculated as 556 mm and 65 mm,respectively.To study seismic responses of the relic,acceleration sensors were set on the showcase bottom and relic top.In addition,a video admeasuring apparatus was used to capture displacement response values of the relic.Shaking table tests were conducted that considered two boundary conditions of the showcase bottom including fixed and free-standing status.Frequency distributions of the showcase under both boundary conditions were obtained by white noise excitation.Three different types of earthquake waves including those of El-Centro in 1940 and Taft and Artificial of Ⅱ site classification were applied to the models in east-west direction with intensities of PGA = 0.1g,0.2 g,0.4 g,and 0.7 g;time duration of 30 s;and time space of 0.02 s.Aseismic parameters such as displacement,acceleration,and dynamic magnification coefficients for both relic and showcase under the various boundary conditions were compared.Results show that under both showcase boundary conditions,relic sliding was minimal under small-intensity earthquake conditions,while the sliding was obvious under those of high intensity.For the duration of the tests,the relic slid under both showcase boundary conditions,and the showcase slid only under free-standing showcase boundary conditions.When earthquake intensity increased to certain degree,slide motion of the relic under fixed showcase boundary condition increased to a more significant degree than that under free-standing showcase boundary conditions.Regardless of showcase status,the prominent frequency factors were far greater than those of the input earthquake waves;thus,the showcase was not damaged significantly.The slide response for the relic under the free-standing showcase boundary condition was more significant under low-intensity earthquakes than that under fixed conditions and was significantly less when earthquake intensity increased,obviously due to friction between the showcase and shaking table.Thus,free-standing museum showcases are helpful for mitigating the slide response of cultural relic contained in them,provided that the distance between each showcase is sufficient to guarantee sliding motion during strong earthquakes.

    • Analysis of Seismic Response and Seismic Checking in A Long-span Continuous Beam Bridge on a High-speed Railway

      2013, 35(2):226-231.

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      Abstract:Considering that earthquakes occur frequently in China,four vertical and four horizontal high-speed railway networks are planned,and 23 provincial capital cities and two-thirds of the cities with populations of more than a million are located in regions of high seismic intensity,seismic design is the controlling factor in the design of high-speed railway bridges.The differences between a high-speed railway bridge and a highway or common railway bridge lie in the following aspects: First,pier,bearing system,and displacement restrictions are required to strictly ensure that high-speed trains remain on the rails.Second,bridges make up a large proportion of the high-speed railway,and most of these bridges are viaducts and long.Third,the high-speed railway will have a major impact,being traffic intensive,high speed,high cost,and so on.Fourth,gravity piers(or hollow piers) are generally used in the substructures of such bridges,and these piers often have large section size and low reinforcement ratio.The long-span continuous bridge is the most widely used bridge type in Chinese high-speed railway construction,and the structural form of "multiple spans as one unit" is often used in this bridge type,with only one fixed pier per unit.Under earthquake force,the inertial force of the superstructure is mainly exerted on the fixed pier,so the fixed pier must meet the requirements of strength and ductility.For this reason,most fixed piers of long-span continuous bridges are reinforced concrete gravity piers.Under frequent earthquake action,piers are required to be elastic,and strength failure criterion can be used to check piers.Under rare earthquake action,because a pier would be in a plastic state,the deformation failure criteria would be used.The seismic checking index for each level is combined with the three-level seismic fortification goal based on the structural characteristics of a long-span continuous beam high-speed rail bridge.A seismic response analysis was performed on an actual bridge by use of a response spectrum method,and elasto-plastic history response analysis and seismic performance evaluation were also conducted.The results showed that the seismic design of the bridge was controlled by the fixed pier.The fixed pier is in an elastic state under low-level earthquake conditions.Under high-level earthquake conditions,however,it enters a plastic state in the longitudinal direction,but the displacement ductility factor is less than the allowable value so it has sufficient ductility capability in reserve.Therefore,the seismic capacity of the bridge meets the three-level seismic fortification goal.

    • Numerical Simulation of Earthquake Damage in Rural Masonry Buildings

      2013, 35(2):232-239.

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      Abstract:Earthquake experience indicates that the buildings of the countryside have sustained more serious damage and destruction than city buildings during recent earthquakes in China.A main reason is that rural buildings have not been strictly designed and constructed according to codes.The Code for Seismic Design of Buildings has been under development for fifty years in China,but it has been given few chances to guide building construction at the countryside's lower economic level.Rural buildings have been constructed by the owners themselves and lack basic earthquake provisions,causing rural buildings to be easily damaged during earthquakes.For this reason,some measures have been proposed in recent years for improving the seismic performance of rural buildings.But most earthquake guidelines have not been verified by building model experiments or actual earthquake experiences.Fortunately,as numerical simulation skills develop,it is becoming possible to simulate the entire earthquake response process for a building.This study proposed a numerical dynamic inelastic earthquake response model for a single-story unreinforced masonry building,using the ABAQUS program.Three levels of earthquake provision were considered:(1) the unreinforced masonry building,with no reinforced concrete(RC) tie columns or RC tie beams;(2) the unreinforced masonry building,including RC tie columns and RC tie beams;(3) the masonry building with reinforced steel in the corners and joints between the horizontal wall and the longitudinal wall and including RC tie columns and RC tie beams.Concrete damaged plasticity was used to represent the behavior of the masonry wall.Masonry in compression was modeled as an elastic-plastic material,and the stress-strain behavior of concrete in compression was assumed to be linear elastic.The earthquake response processes of the three models were simulated from the record of the Wenchuan earthquake,located in Wen County of GanSu province.The analysis results indicated that the numerical method is a better tool for simulating the masonry building earthquake response process.The earthquake measures are very important for improving buildings in the countryside.

    • Study on the Application Effect of Ground-penetrating Radar in Permafrost Engineering Geological Investigation

      2013, 35(2):240-245.

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      Abstract:Research purposes: Ground-penetrating radar is one of the important methods used in permafrost engineering geological investigations.Engineering data in addition to theoretical analysis and field tests of ground-penetrating radar in permafrost engineering geological investigations were used in this study,which summarizes the characteristics of the radar image of the main geologic factors of permafrost regions and analyzes the effect of ground-penetrating radar in permafrost engineering geological investigations.In addition,this paper reports the topics for future analysis and fieldwork.The results show that ground-penetrating radar can accurately classify stratum and aid in determination of the permafrost table and the distribution of permafrost;however,this technology cannot effectively determine the ice content in frozen soil.Moreover,the prospecting effect of ground-penetrating radar is more effective in fine-grained soil than that in coarse-grained soil.

    • Quasi-static Tests of Pile-cap Connections for the Prestressed Spun Concrete Square Piles

      2013, 35(2):246-251.

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      Abstract:Quasi-static tests of six full-scale prestressed spun concrete square piles-cap connections were conducted to investigate the influence of 4 parameters on the seismic behavior of the connection.The results and findings indicate:①With axial load larger than 1 700 kN,failures governed by concrete compression take place in the connected part of the piles due to small eccentricity.②Axial load increases the loading capacity for the connection but on the other hand decreases its deformation capacity.The connection shows considerable deformation capacity under axial load of 1 700 kN.③Connection under diagonal loading condition is statically weaker,while showing better deformation capacity.④With a 50 mm dowel depth into the cap,the connection functions well and is capable of larger deformation.But the corresponding equivalent viscous damping coefficient is lower at failure.

    • The Critical Point Behavior of Seismic Activities Prior to Lushan M_S7.0 Earthquake in 2013

      2013, 35(2):252-256.

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      Abstract:The seismic correlation length prior to the Lushan earthquake(April.20,2013) has been studied by use of single-link cluster(SLC) analysis.The catalogs used were downloaded from China Earthquake Networks Center(CENC,http://www.csndmc.ac.cn).The earthquakes were located in an area centered in the mainshock(30.3N°,103.0°E) and ranging 27°~33° to 100°~106° from 5 years before the mainshock to its origin time.We selected 3.5 as the minimum magnitude and checked the completeness of the catalogs used prior to the mainshock using the Gudengberg formula,which shows good completeness above magnitude 3.5.The results showed that the growing correlation length of earthquakes for moderate-size earthquakes,which had been observed prior to the mainshock nearly two years ago to the origin time,can be fitted well by the power law.At the same time,we have developed a method to test whether or not the result obtained is simply caused by data selection to produce the desired pattern.We selected a time interval before the mainshock in which no great earthquake occurred and several years later when the greater earthquake occurred.The catalogs in the time interval will be analyzed using the same method as the catalogs prior to the mainshock study to check whether the correlation length shows an increase with the power law.We cannot find an obvious increasing process by the power law.For the preparation and occurrence stages of the earthquake process,characterized as a selforganized critical phenomenon,to test directly for growing spatial correlation lengths prior to large earthquakes is an independent approach to detect critical point behavior in observed seismicity.The results from this paper showed that the self-organized critical point characteristic was observed prior to the Lushan 7.0earthquake.The studies in this paper illuminate the notion that the growing seismic correlation length by the power law represents a physical process of criticalpoint characteristics in the source area preparing for a great earthquake.In future work,the predictive power of growing correlation length should be tested.In an area,the grid search technique can be applied to extract regions of growing correlation length systematically from a data set.The estimates for occurrence time,epicenter,and magnitude of expected mainshock may then be obtained from the fitting parameter,critical region,and value of correlation length.For a further reduction of uncertainties in a predictive approach,it also appears promising to combine the concepts of growing correlation length and other predictive methods

    • Retrospective Study on One-year Prediction for 2013 Lushan M_S7.0 Earthquake

      2013, 35(2):257-265.

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      Abstract:The medium-term prediction(one-year scale) is focused on and mainly considered for the master's thesis written by the first author and his student in 2012.Before the earthquake,it predicted that an MS7.0 earthquake would occur in the Xianshuihe seismic belt by means of a triplet method and the regularity of "an earthquake on the bottom follow-up earthquake on the perpendicular fault," and the prediction location was approximately 70~80 km from the accurate circle.In the medium-term(one-year) predictions that aimed at predicting the Yaan MS7.0earthquake,the predictions should be the closet one.The triplet method,the"activity in quiescence" method,and the regularity of"an earthquake on the bottom follow-up earthquake on the perpendicular fault" are retrospectively researched in this paper,and they are shown to have good prediction efficiency.The triplet method is an analysis method based on the time frequency of the M >7.0earthquakes.A specific approach is used for studying the time series of great earthquakes occurring in the past in a certain region by using a time series composed of periodicity,multiple periodicity,and golden section.If they fit well,we can use it for predicting the time of a future earthquake by the time series." Activity in quiescence" was a method for analyzing the seismic activity on the basis of considering the earthquakes in a low-tide period as a precursory index for predicting the earthquakes in a high-tide period.It calls approximately one decade when no M >7.0earthquakes occurred in the Mainland China intermittent period,then subtracts two years from both ends of the intermittent period to eliminate the influence of the start and the end of the earthquake climax;hence,the rest of the period is called the quiet period.In the places where M6.0earthquakes occurred in the quiet period,the M ≥ 7.0earthquakes may occur when the climax of the next earthquakes is reached.The regularity of"an earthquake on the bottom follow-up earthquake on a perpendicular fault" is based on the theory that seismogenic faults interact with each other and then affect another seismogenic fault,and thus,an earthquake is caused.It states that the Wenchuan MS8.0 earthquake in 2008exhibited a shock-adding effect on the intersecting Xianshuihe fault.

    • Gravity Observation in the Eastern Margin of Qinghai-Tibetan Plateau and Reflect to the Lushan M7.0 Earthquake

      2013, 35(2):266-271.

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      Abstract:With the introduction of observation on relative gravity and absolute gravity in the eastern Qinghai-Tibet Plateau,gravity field change of the eastern margin of Tibetan Plateau since 2010 and the reflection on the M7.0 earthquake which occurred on April 20,2013 in Lushan,Sichuan were systematically analyzed.The results showed that:(1)Before the Lushan 7.0 earthquake,the gravity of the eastern margin of Tibetan Plateau changed drastically,and the Lushan earthquake occurred in the turning site of the high gradient zone of gravity variation which was along the southern seciont of Longmenshan fault zone.(2)The Lushan earthquake in 2013was less than 100km from the 2008 Wenchuan earthquake in terms of location,moreover,Lushan and Wenchuan were at the four-quadrant center of gravity change,which indicated that the restoration and change after Wenchuan earthquake had a promoting effect on the Lushan earthquake.(3)A certain medium-term prediction based on the anomaly change of mobile gravity was madebefore the Lushan M7.0earthquake,especially the location prediction.

    • Analysis of Thermal Infrared Anomaly before the Lushan M_S7.0 Earthquake

      2013, 35(2):272-277.

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      Abstract:Aiming at analyzing the thermal infrared anomaly that occurred before the MS7.0 earthquake in Lushan,Sichuan,remotely sensed infrared brightness temperature data from China Geostationary Meteorological satellite FY-2C/E was collected,and the infrared data from the prime period from 1:00 to 5:00 Peking time was selected as the data source.By processing the data to eliminate cloud cover and by using the power spectrum transform method,we analyzed the thermal infrared anomalies in the earthquake temporal evolution diagram and the timing curve of the

    • Seismogenic Mechanism of the 2012 North Sumatra off West Coast Earthquake and Its Influences on Seismicity

      2013, 35(2):278-288.

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      Abstract:On April 11,2012,a large earthquake(MW8.6) and by far the largest strike-slip event ever recorded,struck the west coast of north Sumatra and was followed 2 h later by an MW 8.2 earthquake.A number of issues remain unclear such as the reason for the unusually large strike-slip earthquakes occurring in the intra-oceanic lithosphere,correlations between these two earthquakes,and the manner in which they influence seismicity.Therefore,this paper analyzes the nucleation background of the MW8.6 earthquake according to the region's geological environmentand geophysical observation results.Although the earthquake occurred in the Wharton Basin southwest of the Sunda Trench in the Indian Ocean,the strike-slip faults are well developed with complex deformation and frequent seismic activity.In the movement toward northwest of the Indian

    • Determination of the Direction of the Mean Stress Field in the Western Qilian Mountains through Focal Mechanism Solution Analysis

      2013, 35(2):289-295.

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      Abstract:The western segment of the Qilian Mountains,which is controlled by some tectonic blocks,has complicated geography and geology.This study looked at 14 strong-moderate earthquakes and 66 small-moderate earthquakes from 2001 to 2012,used the stress tensor averaging method to calculate the direction of the mean stress axis in the area,and then analyzed the characteristics of the stress field.Moreover,we compared the results with another inversion result by using the FMSI inversion process.Finally,we conducted a detailed study of the tectonic stress field characteristics of the western segment of the Qilian Mountains.With the stress tensor calculation method,we obtained the average direction of T,B,and P axes by calculating the average stress tensor of focal mechanism solutions from multiple earthquakes.If the earthquake has a relatively independent discrete distribution in the block,we can deduce the direction of the principal stress axes in the regional tectonic stress field on the basis of the average direction of T,B,and P axes.In our research,we selected two groups of data,strong-moderate earthquakes and smallmoderate earthquakes from 2001to 2012.We obtained 14focal mechanism solutions for strongmoderate earthquakes occurring since 1900,with 4above MS6.0and 10between MS5.0and MS 5.9.Furthermore,another was the earthquake that occurred on December 25,1932,the largeChangma MS7.6in the western Changma fault.In addition,we used the CAP method and the vertical P-wave and S-wave amplitude ratio method to calculate the focal mechanisms of smallmoderate earthquakes.The focal mechanisms show that the characteristics of focus are mainly strike-slip and thrust earthquakes.The quantification results for stress tensor in three regions show that the azimuth of maximum principal compressive stress,σ1,is NE,and the horizontally compressed acts show evidence of definite subarea characteristics.

    • Related Analysis of Effecting Errors in Deformation Measurement Accuracy of Four-pass D-InSAR

      2013, 35(2):296-301.

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      Abstract:Differential interferometry synthetic aperture radar(D-InSAR) is further development of InSAR,and four-pass D-InSAR is one type of data processing by this method.Because many uncertain factors affect the accuracy of data processing of four-pass D-InSAR,it is not applied widely in the monitoring of land deformation.However,four-pass D-InSAR does not require an external digital elevation model and has the advantage of a possible guarantee of the accuracy of monitoring deformation.The baseline,visual angle, baseline tilt angle,slope range,satellite orbit height,ground resolution,and other satellite imaging factors significantly affect the capability and accuracy of D-InSAR measurement in monitoring land subsidence;satellite orbit error is the main factor affecting the accuracy of deformation measurement when using four-pass D-InSAR.The difference in satellite orbit and radar frequency is generated by various sensors of satellites acquiring radar images,which could also significantly affect deformation measurement with this method.The system and speckle noise,loss of pixel registration,visual number,and temporal and baseline decorrelation are the main sources of phase measurement error and significantly affect each pixel of images from the coherent radar,for which the phase error affecting the accuracy of deformation measurement when using four-pass D-InSAR is created.The baseline is generated by two different satellite orbits,which causes the baseline error to be systematic;hence,the baseline length error is also systematic.The baseline tilt angle affecting high altitude onboard the satellite is created by various uncertainties of the satellite and changes in baseline length.Consequently,the baseline tilt angle error has an effect on four-pass D-InSAR.The uncertainty of slant range is determined by the delay of the troposphere and ionosphere to the space-borne SAR satellite radio transmission,sampling clock jitter,and uncertainties of timing system of the SAR satellite,for which the interference phase of the InSAR diagram from four-pass D-InSAR is unstable.The uncertainty of terrain factors is generated by variation from the ground flatness,high and low topography,and vegetation coverage in the study area,which prevents the coherent radar images from effectively containing deformation information of target objects;thus,the influence on four-pass D-InSAR is apparent through the terrain factor error.An effective quantitative formula of phase on deformation measurement accuracy of four-pass D-InSAR is presented in this paper on the basis of the basic principle and data processing flow of four-pass D-InSAR.In addition,the effects of baseline length,baseline tilt angle,satellite orbit height,slope range,and terrain factors on deformation measurement accuracy of four-pass D-InSAR are analyzed and discussed.Finally,conclusions of the effects of errors on deformation measurement accuracy when using four-pass D-InSAR are drawn by the quantitative analysis.

    • 2D Simulation of the Strong Ground Motion in Lanzhou Basin with Hybrid PSM/FDM Method

      2013, 35(2):302-310.

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      Abstract:In this study,we simulate two-dimensional(2D) numerical data related to a strong ground motion in the Lanzhou basin using a hybrid scheme based on the pseudospectral method(PSM) and the finite difference method(FDM).The simulation is based on a 10-km-deep focal point,and a 2D profile of five layers is used as a model for analyzing the site response and the peak displacement of the strong ground motion.The results show that the hybrid PSM/FDM method for the seismic wavefield simulation combines the advantage of PSM and FDM and compensates for the disadvantages of these methods.Therefore,the proposed method can betterprocess the calculation of the discontinuous medium surface.The calculation accuracy of this method is similar to that of PSM.First,we simulate the theoretical seismograms and find that the peak ground displacement(PGD)of the vertical is obvious at the basin edge.Then,the wavefield snapshots of the profile at t=3,6,9,12,15,18,21,24,27,and 30sexplain the propagation of the seismic wave,and it is ensured that the amplification of P waves and Sv waves is obvious in the inner basin.The results of the wavefield simulation reveal that the sedimentary basin can amplify a strong ground motion compared with the bedrock,and that the PGD of the vertical in the inner basin is 0.1cm,which is larger by 0.03cm than the PGD near the seismic source.Further,the PGD at the east edge of the basin is larger by 0.02cm than that in the inner basin.However,the PGD of the horizontal in the inner basin is 0.025cm,which is smaller by 0.2cm than the PGD near the seismic source.Therefore,it is known that the PGD of the vertical is larger than that of the horizontal in the inner basin,and the results are opposite near a seismic source,which proves that the influence of a distant earthquake on a tall building is significant.Further,the wavefield simulation revealed a positive correlation between the site conditions and the PGD:if the site conditions are more complex,the PGD will be larger for the same earthquake.Otherwise,the influence of the surface wave of the vertical is more obvious than that of the horizontal at the basin edge,which provides the theoretical evidence for future quakeproof research.

    • New Discovery and Application of Some Historical Data for the M8.0 Earthquake in Southern Wudu in 1879

      2013, 35(2):311-320.

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      Abstract:An M8.0 great earthquake occurred between Wudu and Wenxian,Longnan district,on July 1,1879(May 12,Guangxu 5,Qing Dynasty).The complex geological structure,traffic inconvenience,and lack of systematic data and regional field trips have led to speculations and discussions about the true conditions of the earthquake for half a century.However,many questions remain.Comparative analysis of more than 20 studies concerning this earthquake has revealed that the macroscopic epicenter of the earthquake is located in Qiaotou and Tunzhai(now Tianchi township)along the Yangtang River.Moreover,the magistoseismic area extended to Guoyuan Township in Jiuzhaigou County,Sichuan province,and Liangshui and Shimen Township in Wudu,Gansu province.

    • The Research and Realization for Scanning Missed Seismic Events Automatically

      2013, 35(2):321-325.

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      Abstract:There are more than eight thousands times more than magnitude four in the world ever years.The seismic waves excited by two or more different earthquakes sometimes at the same time reach the observation seismic stations;it is difficult for seismic analysts to manually look for missed seismic events by the automated process software without any tools.The analysts have to spend more time to scan missed event in manual when there are more and more the number of stations in the network.The experience of the analysts determines whether to effectively detect the missed events and experienced analysts can successfully detect missed seismic events by the automated process system in a relatively short period of time.How to reduce the workload of analysts,as well as how to improve the efficiency and accuracy of their work is the issue which we discuss in the paper.The method of scanning the missed seismic events automatically and the software developed base on the method are introduced in the paper.Automatic scanning missed event method can scan the unassociated signal in the automatic process phase and re-associate them to form a new event.It captures the knowledge of experienced analysts and makes that knowledge available to all analyst and uses empirically derived information to identify candidate association sets for a given source region.We divide the world into several geographic focal regions according to the geographical distribution of seismic stations in NDC monitoring system and the earth physics rules.There is a corresponding set of sensitive stations in each certain region.The criteria for the source regions and candidate arrivals are defined in the NDC database tables and user definableoptions to control processing are stored in a parameter file.Each region is given a name,region identifier(number),and upper and lower bounds for latitude and longitude.The scanning software computes an initial P travel-time window for each station to the closest and furthest point in the region.To sum up,the scanning software can scan automatically unassociated seismic signals to form region specific events,according to the slowness and azimuth of signals,and then reduce the number of missed events.The signal to noise ratio,period and amplitude are also considered in the design of software,but tuning these three parameters need long-term statistical analysis,these parameters are not configured in our trial operation stage.In the future,these parameters can be added to the scanning software,no need to modify the program.The scanning software is developed on the platform of Solaris system and Oracle database,the core codes are programmed using standard C language.The software has been integrated into the national data center interaction analysis software and has obtained the good effect in the stage of trail operation.It greatly reduces the workload of analyst and improves the seismic bulletin.The change of seismic stations can influence the efficiency of the scanning software,so,the operations parameters need timely be adjusted according to the change of the monitoring station and monitoring network in order to improve the accuracy of the scanning software.

    • Component Azimuths of Regional CEArray Stations Checked by Teleseismic P-wave Particle Motion

      2013, 35(2):326-333.

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      Abstract:Orientation accuracy of three components of station seismometers is very important for modern seismology research.Many aspects of modern seismic studies require rotating the BHN,BHE,and BHU as three-dimensional orthogonal coordinate components of particle motion;that is,radial(horizontal direction of incidence),horizontal(in the horizontal plane perpendicular to the incident direction),and vertical.If the station seismometer's BHN component direction and the true north direction N are really larger than the azimuth deviation,then the radial and transverse components will have a greater system deviation,which is based on the back azimuth value.This will affect the authenticity and reliability of modern seismic studies,such as shear-wave splitting SKS results,and also confuse seismic interpretation.For many years,seismic workers at home and abroad have attached great importance to the seismometer azimuth's accuracy and correction testing for basic research.If P-waves are compressed through horizontal layered anisotropic media to seismic stations,then the particle trajectories will be in the large in-plane circle composed of the seismic focus,the seismostation,and the geocentre.Seismic P-waves in the plane incident to station direction(radial or station azimuth direction)were also determined tohave radial(plane incident)P-waves with the greatest polarization energies in the plane perpendicular to the incident direction of landscape orientation with the lowest vibrational energy.If BHN coincides with the north direction N (BHE direction coincides with the East direction E),the rotation angle from BHN to the P-wave plane incident direction(energy maximum polarization direction)will be the seismostation to seismic focus's back azimuth.If the seismometer station BHN direction and the North direction N slightly deviate,the rotation angle from BHN to Pwave plane incident direction(polarization energy maximum)will not equal the seismostation to seismic focus's back azimuth.From the seismostation-seismic focus back azimuth angle and the rotation angle determined from the BHN/BHE components to the maximum polarization energy's direction,the seismometer BHN component's azimuth deviation could be obtained.Using an SNR-weighted multievent method and teleseismic P-wave particle motions,Niu(2011)found that about one-third of the CEArray stations have some sort of problems,including misorientation of the two components,mislabeling of BHN and BHE components,as well as polarity reversal in one or more components,all of which were brought to the attention of the China Earthquake Administration and seismic data users.In this study,we rechecked the component azimuths of the circum-Ordos block of CEArrays from P-wave particle motions of 73 M >7teleseismic events from August 2007through March 2011.Considering possible seismometer re-installation,we estimated the north-component azimuth for each station by analyzing the time series of the calculated azimuths of each individual event.Our calculated azimuths are very consistent with the results of Niu(2011),which implies that the CEArray does have a problem with misorientation.The teleseismic P-wave particle motion method can be used to effectively check the seismometer stations' horizontal azimuth deviations.Therefore,in modern seismology research such as SKS splitting with CEArray data,users should pay particular attention to component misorientation,polarity reversal,and mislabeling problems.

    • Research on the Technology of Extracting Earthquake Precursor Information from Groundwater Level

      2013, 35(2):334-341.

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      Abstract:Our country has established an improved seismic underground fluid observation network.Underground water level is an important earthquake precursor factor and is applied to prediction measures.The observation data of groundwater level is an integrated parameter and includes many components determined by such factors as precipitation,atmospheric pressure,Earth tide,and geological structures.To highlight the influence of tectonic forces on groundwater level and to recognize the earthquake precursorinformation obtained by this parameters must be separated from original observation data.Components influenced by Earth tide and atmospheric pressure can be separated on the basis of a widely used theory.The influence of climate conditions on underground water level at a watershed scale,changes of which are long-term and periodic,can be separated through smooth processing methods.On the contrary,rainfall peaks influence underground water level,which reduces the effects created by structure forces;therefore,the identification of earthquake precursor information is difficult.In order to highlight tectonic forces on groundwater level,it is necessary to separate the peak value of rainfall effects on underground water level.In our study,we regarded the observation data of groundwater level as a linear combination of all of the components.Changes caused by Earth tide and atmospheric pressure were first separated according to the BAYTAP-G procedure.Then,because quick and slow response existed in the influence of rainfall on groundwater level,these effects were distinguished by applying base flow separation methods.Changes induced by rainfall were separated from groundwater level by using base flow separation methods.By analyzing the relationships between the curve feature of every component and local seismic activities,local earthquake precursor information on groundwater

    • Characteristics of Late Quaternary Tectonic Activity of Middle-western Segment of Heihe Fault in Southwestern Part of Yunnan Province

      2013, 35(2):342-353.

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      Abstract:On November 6,1988,two earthquakes with a magnitude >7 occurred in the Lancang and Gengma area of the southwestern part of the Yunnan province.The maximum intensity of the M7.6 Lancang earthquake was IX on the Chinese scale,which is similar to the Modified Mercalli scale.The surface rupture of the tectonic activity of the Lancang MS7.6 earthquake occurred because of the earthquake-related extensional ground cracks and small fault scarps in the epicentral region. The area within which the cracks and small scarps occurred was approximately 35-km long and 3-km wide.The maximum vertical and the dextral horizontal offsets were 1.5mand 1.4m,respectively.The M7.6earthquake showed complicated earthquake-generating tectonics and formed a separate obvious seismic deformation belt along the Heihe and Lancang faults.The Heihe fault is one of the seismogenic faults of the 1988 M7.6event of Lancang.The Heihe fault,located in the southwestern part of the Yunnan province,having a length of 168km and a trend of 280°~310°,is an active fault zone in the late Quaternary,which is mainly a right-lateral strike slip with a dip slip.It turns out that the Heihe fault zone can be divided into three secondary fault segments,namely,Cangyuan-Mujia(F1-1),Mujia-Nandai(F1-2),and Nandai-Mengwang(F1-3).The activity gradually becomes weak when this segment of fault travels eastward.Through satellite image interpretation and field geological investigation,we studied the geological and geomorphologic characteristics of activity along the middle and the western segments of the Heihe fault in this research.The middle and western segments of the Heihe fault,having a length of 88km and a trend of 280°~310°,is an active fault zone in the late Quaternary,which is mainly a right-lateral strike slip with a dip slip.A variety of dislocation landforms have been formed along the fault by the new tectonic activities since the late Quaternary,such as the dextral dislocation of gullies and ridges,fault trenches,fault passes,fault scarps,and pits.A series of dextral dislocations of gullies and ridges,and scratches on the cross section along the fault show that the middle-western segment on the Heihe fault is dominated by a right-lateral strike slip.In the Xuelidazai village,the age of the displaced stratum is(2 530±25)a.B.P.,and on the faultplane,a loosely consolidated gouge is developed across several cross sections of the fault.This implies that the latest active time of the middle-western segment on the Heihe fault is the late Holocene.Near Baishuijing,there are synchronous dextral dislocations of four small gullies because of the dextral movement of faults;these dislocations range from 9to 14m.By using the differential GPS measurement,the sample dating and the regional comparison of the fault slip rate,we calculated the right-lateral strike slip rate of the segment to be(3.54±0.78)mm/a.This value agrees with the regional characteristics of the fault slip rate.

    • Research on Geochemical Characteristic of Hot Spring Water and Seismicity in Fault Zone Based on MATLAB

      2013, 35(2):354-359.

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      Abstract:The Matlab high-performance language for technical computing integrates computation,visualization,and programming in an easy-to-use environment where problems and solutions are expressed in familiar mathematical notation.It allows you to solve many technical computing problems,especially those with matrix and vector formulations,in a fraction of the time it would take to write a program in a scalar noninteractive language.The Matlab had a important application in seismic studies,such as,the ZMAP software used for scanning b value and application of Matlab software on intensity rapid report of Tianjin strong mation network.Authors developed the analysis software of the subsurface fluid based on Matlab,which combined with the function of some other geochemical software.This paper mainly discussed the water quality analysis by means of the software,and studied on the spring water in the north margin of western QinLing fault zone and comparatively analyzed the chemical composition characteristics of hot spring water in Wushan,Jiezi and Qingshui.In this paper,the types,water qualities,supply sources,the state of water-rock reaction and circulation depth of the water were discussed.And the paper analyzed that the circulation depth of hot spring water impacted on the seismicity of fault zone.In this paper,we drew the linear correlation diagram ofδDandδ18 O of hot spring water samples in the north margin of western Qinling fault zone.By the composition analysis of Hydrogen and Oxygen isotopes,it was showed that the supply sources of the water in three springs are precipitation and the isotope exchange effects caused positive shift of the 18 O.Based on Rectangle hydrochemical diagram,it was the results that the hot spring water in Wushan and Jiezi was belonged to Na-HCO3·SO4·Cl and carbonated water of hydrochemical type,but the water in the Qingshui hot spring was belonged to Na-SO4·Cl and sulfuric water of hydrochemical type.In overall,three hot springs was the type of low salinity water.Because the different reactions were taken place between water and surrounding rock during the water cycle,chemical composition type of the spring water in Qingshui distinguish the Wushan and Jiezi.We came to some conclusions by mean of comparing depth of the spring water cycle with seismic activity of fault zone.The hot spring water with shallow depth of the water cycle,in Wushan and Jiezi,and the seismic activity was frequent in the local fault.But,the water-circulating depth of the spring water in the Qingshui was deep and the seismic activity of local faults was weak.This paper was showed that it were a correlation between the depth and seismic activity.The water during depth circulation had a strong weakening effect on its surrounding-rock on the fracture.The deep fluid provided with greater pore-pressure could reduce the effective positive pressure of fracture surface.The water with deeper cycle had a the higher level of weakening effect on fracture and caused the lower strength of fault zone.It affected the fault activity.All in all,this paper was showed that the geochemical characteristics of the spring water were differences between Qingshui and Wushanand Jiezi.In addition,whether it is a correlation with the size of fault activity will be required more in-depth study.

    • Status of Seismic Source Spectral Parameters in the Jiaodong Peninsula

      2013, 35(2):360-365.

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      Abstract:Source parameters calculations are generally carried out in the frequency domain.Seismic wave data from station records can be used for site response,instrument response,geometric diffusion path attenuation,and focal radiation directivity factor correction.A genetic algorithm can be used to obtain the parameters of low-frequency spectral amplitude limit and corner frequency,and thus,the theoretical formula for calculating stress drop,source radius,and seismic moment.The geological structure of Jiaodong Peninsula is complex.The area spread by the Jiaodong fault was uplifted,and the area of the northern Yellow Sea fault was bent,so the Jiaodong Peninsula fault structure is mainly monoclinic or relief synclinic.Brittle faults are well developed,mainly related to the eastern section of the Yanshan-Bohai fault zone.In contrast,at the intersection with the Tan-Lu fault in the Bohai are two sets of faults in the NNE-NE and NWW directions.The faults in the area are strong,and the structure is extremely complex;this was a high activity area in the North China earthquake.In recent years,the seismic activity has concentrated and strengthened.Regional stress changes have been analyzed in recent years in order to study the risk to Jiaodong Peninsula of strong earthquakes.Based on digital seismograms of Jiaodong Peninsula and the surrounding areas recorded by the Shandong digital seismic network since 2010,the Brune model,combined with a genetic algorithm,has been used to calculate the spectral parameters of 134earthquakes above 2.0in the Jiaodong Peninsula.Results show that seismic moments were between 9.76×1011 N·m and 5.9×1014 N·m;pressure drops were between 0.017MPa and 25MPa(0.97MPa mean);and apparent pressures were between 0.06 MPa and 10.2MPa(0.396MPa mean).Seismic moment,stress drop,and apparent stress were positively correlated with magnitude,with the magnitude of the rise increasing.By using a linear fit of robust regression functions,aquantitative relationship has been developed for the Jiaodong Peninsula,which is consistent with the findings of other scholars.The relationship between corner frequency and magnitude is not obvious;seismic moment and corner frequency were negatively correlated.According to the quantitative statistical relationships between the Jiaodong Peninsula source parameters and magnitude(in addition to the effect of magnitude),and by the changes in stress drop and apparent stress over time,we can clearly see that a Jiaodong Peninsula stress adjustment has caused the stress to currently be in a period of weakening,compared to its previous high-stress state.

    • Comparative Analysis of Zhangjiang Station Surface and Deep Seismic Observation

      2013, 35(2):366-371.

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      Abstract:Twenty-seven deep seismic observation stations are planned for construction in the administrative area of Shanghai to provide a comprehensive observation system of deep earthquakes,and two deep seismic observation stations will be constructed in Zhangjiang,Pudong district,and the Yangtze River farm,Chongming district,in accordance with China's Eleventh Five-Year Plan.The deep well station in Zhangjiang has been completed and has passed the acceptance stage.Ten test items have been installed including a magnetometer;strain gauge;inclinometer;seismometers;pore pressure,temperature,and water temperature instruments;a water meter installation site in a deep well,a surface-installed strong motion seismograph,and a global positioning system (GPS).In addition,the surface is equipped with a pressure gauge,a temperature gauge,and other auxiliary observation tools.In this study,the micro-tremor and dynamic range data of the Zhangjiang surface station and deep well station data are compared and analyzed systematically.We obtained the following preliminary results:The root mean square(RMS)value of background noise in the deep well is smaller in orders of magnitude than that at the surface station.It can accurately record micro-tremors because of only slight disturbances by the external environment.The seismic signals of deep well observation are the most accurate.The dynamic range of measurement stations effectively reflects the instrument's performance indicators to determine the background environment interference level recorded by the maximum dynamic range of the seismic signal.Due to the superposition station environment noise and seismic signal,the instrument is not up to the dynamic range of design and can only achieve an effective dynamic range of measurement.The effective dynamic range of the deep well station exceeds 30%of that of surface stations;therefore,it can produce a broader range of micro-tremors.Range surface frequency is within 0.3~2.5;the deep well station has low-frequency noise and nearly high-frequency at 25Hz.A comparison of deep bench surface stations reveals that environment noise is much smaller,particularly in the low-frequency range.Moreover,with reference to analysis of data from the Shanghai telemetry seismic network of various types of base background noise,the dynamic range of noise at the Zhangjiang comprehensive deep well and those of the Shanghai network deep wells are consistent.Therefore,comprehensive visible data for the deep seismic section is unaffected by the noise integrated system.With the accelerated process of city development,environmental noise will increase;therefore,the deep well seismometer observation method is more reliable than surface seismometer observation.Completed construction of the seismic section of the deep borehole project can provide greater precision and better quality of observation data to further improve the earthquake monitoring capacity of Shanghai.

    • Analysis on Sand Bed Stress Observation Instrument through Data Changes at Huai'an Seismic Station

      2013, 35(2):372-377.

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      Abstract:The sand bed stress instrument is a precursory observation instrument used to transmit crustal stress signals via particle media,which entails sensors buried in the sand underground to receive the stress generated by the sand movement surrounding the sensor.It is widely accepted that the collision between sand grains can lead to stress changes in the Earth's crust and may affect the direction and numerical value of the crustal stress.To demonstrate the manner in which data recorded by the sand bed stressstress observation instrument,among which the frequency at 1.1574x10-5 Hz was the strongest signal,followed by 2.314 8x10-5 Hz.These frequency components included in the sand bed stress data clearly show the periodic tidal variations of the solid Earth under the tidal forces of the sun and the moon.A tidal cycle consists mainly of one-day waves and half-day waves;the former have the greatest influence on periodic tidal variations.In addition,we compared the stress data of sand bed in Huai'an with those in Xiji,Beijing,and Putian,Fujian province,to determine that despite the differences in geological environments,they exhibited the same trend of rise and fall in value,which obviously show a synchronous change and a consistent annual variation.The changes in stress data from the Huai'an station create an effective model for studying seismic activity.Such changes reflect the entire processes of major earthquake seismogenic phenomena,which include loading,rallying,unloading,and rising,in addition to higher frequency signal loading or unloading prior to a major earthquake with a frequency between 0.3and 0.4.On the contrary,when a moderate earthquake occurs,the sand beds near seismic stations exhibit short stress seismogenic phenomena,which includes loading,unloading,and rising.Moreover,the sand bed stress data curve shows abnormal fluctuation changes in waveforms.

    • The Assessment of Positioning Result of Northwestern Regional Automatic Earthquake Rapid Report System

      2013, 35(2):378-384.

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      Abstract:The northwestern regional automatic earthquake rapid-report system,the center of which is located in earthquake networks center of Shaanxi province,is one of five such systems under the China Earthquake Administration.The principal rapid-report range includes Shaanxi province,Gansu province,Ningxia Hui Autonomous Region,western Inner Mongolia Autonomous Region,and eastern Qinghai province.The system,which is based on software in a regional digital seismic network for a real-time earthquake rapid report system,relies on the network platform of the Earthquake Administration of Shaanxi province and accepts data from all seismic earthquake stations in Shaanxi,Gansu,Ningxia,and Qinghai,in addition to those west of Inner Mongolia.On July 1,2009,this system officially assumed primary responsibility for the northwestern regional automatic earthquake rapid report,by which northwestern region M≥3.0earthquakes are automatically output and uploaded to the China earthquake networks center.This system can automatically analyze seismic phases of earthquakes on this region and neighbor areas and gives three elements of earthquake including origin time,earthquake magnitude,and earthquake epicenter.In addition,region M≥4.0earthquakes are recorded by the automated rapid reporting mobile message service.This study selects 173natural earthquakes and 11non-natural earthquakes from the earthquake catalog,from July 1,2009,to August 31,2011.One hundred fiftysix earthquakes output from the northwestern regional automatic earthquake rapid report system correlate with earthquakes listed in the catalog,including 149natural earthquakes(86.1%)and 7 non-natural earthquakes(63.6%).This study has determined that 24earthquake had been not detected by this automatic system,all of which occurred in western Gansu and the Qinghai-Tibet plateau area,where earthquake seismic the network layout is relatively sparse.Earthquakes occurring in areas in which seismic stations layout are relatively reasonable,such as Shaanxi,Ningxia,eastern Gansu province,western Inner Mongolia,and eastern Qinghai province,were all reported by this system.This study also analyzes the deviation and accuracy of positioning results of 149natural and 7non-natural earthquakes on the basis of correlation to the those listed in the earthquake catalog and northwestern regional automatic earthquake rapid report system.This paper shows that in 97.3%of natural earthquakes,the deviation of origin time is less than 5s;in 96%,deviation of the earthquake epicenter is 5to 30km;in 94%,deviation of earthquake depth is less than 5km;and in 68.5%,deviation of magnitude is less than 0.3.All 7non-natural earthquakes were related to a coal mine collapse earthquake with deviation of origin times of less than 5s.Therefore,the performance has achieved first-class competition status as outlined by the 2010appraisal standard for rapid reporting.Moreover,4achieved second-class for earthquake epicenter location accuracy;2reached third-class,1reached fourth-class in positioning accuracy.One earthquake had a magnitude deviation of 0.2;that of all other non-natural earthquakes was greater than or equal to 0.3.In addition,this paper analyzes the reasons why minor earthquakes are not recognized by system or are output with large deviation.According to the task of the northwestern regional automatic earthquake rapid-report system and research of the northwestern region seismic and seismic network layout,this study also provides suggestions for integration and improvement of the automatic earthquake rapid report system,which include relaxing the requirement for magnitude deviation;optimizing the layout of Qinghai networks;increasing the number of stations in mid-and western Qinghai and in northern Shaanxi;and optimizing existing processing software.

    • Research on the Precursor of Moderate Earthquakes before M≥5.0 Seimic in the Northeast Region

      2013, 35(2):385-393.

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      Abstract:In this paper,three parameters(E,T,and R) were used as tools to describe the activities of moderate earthquakes defined by statistical analysis of 11 earthquakes(M≥5.0) in the northeast region of China.The results showed that seismic activity in this area had obvious regional characteristics such that intense seismic activity of ML≥4.0 earthquakes was observed prior to all M≥5.0 earthquakes in Liaoning and to the west of the Nenjiang fracture.The final moderate earthquakes prior to the M≥5.0 earthquakes generally occurred within six months.The interval average was three months;the shortest period was 0.7month in Liaoning Province.In addition,the interval ranged from two to nine months with a four-month average west of the Nenjiang fracture.However,intensive moderate earthquake activity was not observed prior to M≥5.0earthquakes east of the fracture.The probability of the expected M≥5.0earthquake occurring in the area of Yingkou-Haicheng-Xiuyan was more than 75%,which was accompanied by enhanced moderate earthquake intensity.If a foreshock sequence existed,its epicenter was located in the scope of 22km near the larger earthquake.Essentially,the epicenter of M≥5.0earthquake occurring to the west of the Nenjiang fracture was located in the vicinity of the initial or latest moderate earthquake area,at a distance of 11~67km.Therefore,the ETR method has some significance in determining the epicenter of next M≥5.0earthquake after the occurrence of moderate seismic activity

    • Study on Model Building of Post-earthquake Intensity in Chongqing and Its Adjacent Areas

      2013, 35(2):394-400.

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      Abstract:After an earthquake,the earthquake disaster rapid assessment team needs very detailed information,such as an intensity distribution map.If we can study several kinds of different intensity distribution evaluation models in support of the emergency database and compare the difference between disaster evaluation results from different models,the final result will have greater credibility.In this study,the research area of focus was Chongqing and its adjacent areas.The research analyzed 19 earthquakes since 1960,collected and digitized 19seismic intensity isoseismal maps,and acquired a total of 46 isoseismal data sets,including long axis,short axis,and total area,for a data total of 141.In accordance with the characteristics of historical isoseismals,the isoseismals were processed as ovals.In this study,the researcher looked at the epicenter distribution of earthquakes in Chongqing and the vicinity,the intensity data,and the distribution of seismic magnitude and intensity.Through regression analysis,an intensity distribution evaluation model was developed on the basis of the seismic intensity attenuation relationship,and the results from the model were compared with those from other models,which yielded a figure representing the comparison.The attenuation relationship of the earthquake in Chongqing and its adjacent area was compared with Suyun Wang,in China's eastern region;Jianqi Lu,in a moderate earthquake area,and Jiancheng Lei,in Sichuan Basin.To make the seismic intensity attenuation curve closer to the actual situation with respect to far-field and near-field intensity,additional measures were needed to improve the distribution of the data.Hence,the author developed intensity distribution evaluation models based on the length of the prolate axis and the minor axis,and area statistics.The author developed different fitting curves for(1)magnitude V long shaft fitting,(2)magnitude V short axial fitting,(3)magnitude VI long shaft fitting,and(4)magnitude VI short axial fitting.Comparisons were made with one magnitude degree above the intensity area,for the intensity I relationship,and for the length of shaft radius ratio.Last,the author used the examples to verify the above three kinds of models.The model based on the attenuation relationship and the model based on"Wang Jinglai" give intensity in two mutually perpendicular directions with distance attenuation,and the model based on the area is the seismic intensity distribution on the surface.The former two models are one-dimensional,and the third is two-dimensional.If an earthquake of grade IV or V happened in Chongqing and its adjacent areas,the author calculated three kinds of intensity distribution evaluation models,getting long and short axis radii.The first two models'calculation results were more closely matched and so are deemed the best by the author.Because the sample size is small,we will expand the research area in the next study to include a destructive earthquake region.Furthermore,we will include methods of data correction in the earthquake disaster loss assessment process in order to more closely approximate the true mean variance regression relationship.The shape of the intensity distribution curve was very significant for the earthquake disaster loss assessment.

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