Fourier spectra and acceleration response spectra of near-field acceleration records of the 2008 Wenchuan Earthquake have been calculated.Relative fundamental frequencies(or predominant periods) were characterized.The...Fourier spectra and acceleration response spectra of near-field acceleration records of the 2008 Wenchuan Earthquake have been calculated.Relative fundamental frequencies(or predominant periods) were characterized.Then,the natural frequencies of a range of slopes with different geometric characteristics,such as height,slope ratio,and pattern,were analyzed.The seismic responses of the slopes were compared,and the variability of seismic response with the above geometric elements was found.Results show that if slope height increases,and provided that other conditions are unchanged,the natural frequency of the first mode of a doublesurface slope will change as a power law.However,natural frequencies will diminish(based on a parabolic function) as the slope angle becomes large.Both the surface pattern and the number of surfaces on a slope can have a great impact on the seismic response of the slope.Moreover,within a certain range of slope heights or angles,either height or angle will also greatly influence the variability of the seismic response.The results of this research will be helpful to understanding seismic dynamic response features and explaining the ways that slope stability can be affected by earthquakes.展开更多
To evaluate the coupling pounding-friction effect between bridge girders and retainers and its influence on bridge seismic response, a reinforced concrete （RC） continuous bridge is selected as the research object. T...To evaluate the coupling pounding-friction effect between bridge girders and retainers and its influence on bridge seismic response, a reinforced concrete （RC） continuous bridge is selected as the research object. Three bridge finite element （FE） models were built using OpenSees, in which the longitudinal and transverse pounding elements, as well as the transverse failure element of bearings were introduced. Based on this, tire seismic response analysis considering the coupling pounding-friction effect was conducted for the continuous bridge subjected to bi-directional ground motions. Furthermore, the influential parameters were analyzed. The analysis results indicate that the coupling pounding-friction effect can alter the internal force distribution of the bridge structure and generate additional torsional force to bridge columns. The friction coefficient and longitudinal pounding gap size are two important factors. The appropriate friction coefficient and longitudinal pounding gap size can significantly reduce seismic response of girders, and effectively transfer part of the girder inertia force from the fixed columns to the sliding columns, which can reduce the seismic demands of the fixed columns and improve the seismic performance of continuous bridge structures.展开更多
The basic element in any sustainable dam project is safety, which includes the following safety elements： O structural safety, dam safety monitoring, operational safety and maintenance, and emergency planning. Lon...The basic element in any sustainable dam project is safety, which includes the following safety elements： O structural safety, dam safety monitoring, operational safety and maintenance, and emergency planning. Long-term safety primarily includes the analysis of all hazards affecting the project; that is, hazards from the natural environment, hazards from the man-made environment, and project-specific and site-specific hazards. The special features of the seismic safety of dams are discussed. Large dams were the first structures to be systematically designed against earthquakes, starting in the 1930s. How- ever, the seismic safety of older dams is unknown, as most were designed using seismic design criteria and methods of dynamic analysis that are considered obsolete today. Therefore, we need to reevaluate the seismic safety of existing dams based on current state-of-the-art practices and rehabilitate deficient dams. For large dams, a site-specific seismic hazard analysis is usually recommended. Today, large dams and the safety-relevant elements used for controlling the reservoir after a strong earthquake must be able to withstand the ground motions of a safety evaluation earthquake. The ground motion parameters can be determined either by a probabilistic or a deterministic seismic hazard analysis. During strong earthquakes, inelastic deformations may occur in a dam; therefore, the seismic analysis has to be car- ried out in the time domain. Furthermore, earthquakes create multiple seismic hazards for dams such as ground shaking, fault movements, mass movements, and others. The ground motions needed by the dam engineer are not real earthquake ground motions but models of the ground motion, which allow the safe design of dams. It must also be kept in mind that darn safety evaluations must be carried out several times during the long life of large storage dams. These features are discussed in this paper.展开更多
In this paper, the verticalseismic effects on tunnels are studied based on a classic mass–damper–spring model. An analyticaldiscrete modelof urban underground tunnels subjected to verticalearthquake excitations is p...In this paper, the verticalseismic effects on tunnels are studied based on a classic mass–damper–spring model. An analyticaldiscrete modelof urban underground tunnels subjected to verticalearthquake excitations is proposed by considering the first verticalvibration mode. Taking a light railproject in Tianjin as an example, this study uses the proposed discrete modelto analyze the displacements of tunneland soilunder verticalearthquake excitations. The soildisplacement responses at different tunnellocations are analyzed with linear random vibration theory.The computationalcost is greatly reduced using the proposed model. It can be seen that different from the case of horizontalearthquakes, the displacement responses under verticalearthquake excitations keep growing after seismic acceleration reaches its peak for a short duration, and then,they begin to decay. The soils at different positions around the tunnels have large relative displacement under verticalearthquake excitations. Moreover, a finite-element modelis also established for displacement responses using ABAQUS.The comparison with the results of the finite-element modelshows that the results of the proposed discrete modelare available.展开更多
Probabilistic analysis is a rational approach for engineering design because it provides more insight than traditional deterministic analysis. Probabilistic evaluation on seismic stability of three dimensional (3D) sl...Probabilistic analysis is a rational approach for engineering design because it provides more insight than traditional deterministic analysis. Probabilistic evaluation on seismic stability of three dimensional (3D) slopes is studied in this paper. The slope safety factor is computed by combining the kinematic approach of limit analysis using a three-dimensional rotational failure mechanism with the pseudo-dynamic approach. The variability of input parameters, including six pseudo-dynamic parameters and two soil shear strength parameters, are taken into account by means of Monte-Carlo Simulations (MCS) method. The influences of pseudo-dynamic input variables on the computed failure probabilities are investigated and discussed. It is shown that the obtained failure probabilities increase with the pseudo-dynamic input variables and the pseudo-dynamic approach gives more conservative failure probability estimates compared with the pseudo-static approach.展开更多
The April 20,2013,Ms 7.0 Lushan Earthquake was a major earthquake that followed the Ms 8.0 Wenchuan Earthquake on May 12,2008.Frequent earthquakes have caused heavy casualties and property loss in Western Sichuan.Eart...The April 20,2013,Ms 7.0 Lushan Earthquake was a major earthquake that followed the Ms 8.0 Wenchuan Earthquake on May 12,2008.Frequent earthquakes have caused heavy casualties and property loss in Western Sichuan.Earthquake disasters are often closely related to the amplification effect of ground motion.Studying the ground motion characteristics of near-surface geological structures helps to understand the distribution of potential earthquake disasters.In this study,we investigated ground motion amplification in the downtown area of Lushan using numerical simulation and aftershock data from the Lushan Earthquake.Using the Lushan earthquake aftershock data from nine seismic stations distributed in the area,the amplification effect of the sites was determined using the"reference site spectral ratio"method.The results show that the frequency of the ground motion amplification in the area was in the range 5–10 Hz,and the corresponding amplification peak was from 3 to 14.Among the study sites,the amplification(14 times)at L07 was the most prominent.To study further the amplification characteristics,shear-wave velocity models for the structures under these sites were established using passive-source Rayleigh surfacewave exploration.One-dimensional(1 D)and two-dimensional(2 D)seismic amplification effects were simulated using horizontally propagating shear-wave modeling.Except Site L07,the 1 D simulation results of each site well reflected the variation feature of the seismic amplification on the frequency band below the observed peak frequency,although the overall simulated amplification peaks were smaller than the observed results.The 2 D simulation of the remarkable amplification phenomenon at L07 was in better agreement with the observation result than was the 1 D simulation,indicating that the seismic amplification in the Modong area is influenced by lateral variation of the Quaternary sediments.展开更多
To find the distribution patterns of dynamic amplification coefficients for dams subjected to earthquake, 3D seismic responses of concrete-faced rockfill dams with different heights and different shapes of river valle...To find the distribution patterns of dynamic amplification coefficients for dams subjected to earthquake, 3D seismic responses of concrete-faced rockfill dams with different heights and different shapes of river valley were analyzed by using the equivalent-linear model. Statistical analysis was also made to the seismic coefficient, and an empirical formula for calculating the maximum acceleration was provided. The results indicate that under the condition of the same dam height and the same base acceleration excitations, with the increase of the river valley width, the position of the maximum acceleration on the axis of the top of the dam moves from the center to the riversides symmetrically. For the narrow valleys, the maximum acceleration occurs in the middle of the axis at the top of the dam; for wide valleys the maximum acceleration appears near the riversides. The result negates the application of 2D dynamical computation for wide valleys, and shows that for the seismic response of high concrete-faced rockfill dams, the seismic coefficient along the axis should be given, except for that along the dam height. Seismic stability analysis of rockfill dams using pseudo-static method can be modified according to the formula.展开更多
Using the four phases (1996～1999) of re-surveying data from the GPS network along the Shanxi fault zone, the recent state of horizontal movement of the fault zone and its relation with the Datong-Yanggao M5.6 earthqu...Using the four phases (1996～1999) of re-surveying data from the GPS network along the Shanxi fault zone, the recent state of horizontal movement of the fault zone and its relation with the Datong-Yanggao M5.6 earthquake (November 1, 1999), which took place on the north end of the monitored area, are analyzed. In the focal region, three areas with relatively higher strain (1×10 -6) appeared in Xinzhou and to the northeast of Jiexiu. The Shanxi fault zone is mainly controlled by the WNW-ESE-trending compressive stress field and the NNE-SSW-trending tensile stress field, and it does not have strike-slip movement. When examined for long-term tendency, attention should be paid to the junctures between the three moving elements.展开更多
A method combining the pseudo-dynamic approach and discretization technique is carried out for computing the active earth pressure.Instead of using a presupposed failure mechanism,discretization technique is introduce...A method combining the pseudo-dynamic approach and discretization technique is carried out for computing the active earth pressure.Instead of using a presupposed failure mechanism,discretization technique is introduced to generate the potential failure surface,which is applicable to the case that soil strength parameters have spatial variability.For the purpose of analyzing the effect of earthquake,pseudo-dynamic approach is adopted to introduce the seismic forces,which can take into account the dynamic properties of seismic acceleration.A new type of micro-element is used to calculate the rate of work of external forces and the rate of internal energy dissipation.The analytical expression of seismic active earth pressure coefficient is deduced in the light of upper bound theorem and the corresponding upper bound solutions are obtained through numerical optimization.The method is validated by comparing the results of this paper with those reported in literatures.The parametric analysis is finally presented to further expound the effect of diverse parameters on active earth pressure under non-uniform soil.展开更多
This paper is dedicated to the study of the seismic performance of an existing RC （reinforced concrete） bridge localized in a region of moderate seismicity. The bridge has six spans and piers with very different hei...This paper is dedicated to the study of the seismic performance of an existing RC （reinforced concrete） bridge localized in a region of moderate seismicity. The bridge has six spans and piers with very different heights, three of which are monolithically connected to the deck. To understand the roles of the different pier sizes in the overall behavior, several analyses were carried out in the longitudinal direction： （1） linear dynamic approach; （2） non-linear static approach; （3） non-linear dynamic approach. Linear dynamic analysis was made in order to design the bridge for the ultimate limit state considering the largest value of the ductility factor. No safety verification was made for the other loads. Using non-linear static analyses, sensitivity was performed to check the influence of reinforcement quantities of each pier on the overall behavior of the bridge under Lisbon seismic action. For the non-linear dynamic approach, a series of strong motion records compatible with the EC-8 spectrum for Lisbon area were generated. The very same combinations of reinforcement quantities were studied. Comparisons between static and dynamic non-linear analysis were made to confirm the validity of the first one in the case under analysis, where the period of vibration is quite high.展开更多
A statistical analysis on earthquake activity in the Kashi-Wuqia intersection area triggered by earth tide is done by Schusters test and the Permutation test on daily and monthly scales. The north-south,east-west comp...A statistical analysis on earthquake activity in the Kashi-Wuqia intersection area triggered by earth tide is done by Schusters test and the Permutation test on daily and monthly scales. The north-south,east-west component of the tidal force and tidal body stress are chosen as the tidal curve in the daily scale. The results show that most of the earthquakes occurred near the maximum 0° of the three kinds of tidal curves,the predominant tidal phases of the earthquake are- 5. 86°,6. 60° and- 15. 52°,and the frequency of the earthquakes increases with the increase of the tide; with three kinds of tidal curves( the north-south,east-west component of the tidal force and tidal body stress),the p S of Schusters test for all the earthquakes is 10. 52%,2. 40% and 2. 06%,and the p P of the Permutation test is 10. 90%,2. 40% and 2. 06%,and the results of p S and p P based on the east-west component of the tidal force and tidal body stress are below the threshold of 0. 05 that tidal triggering of earthquakes. In the monthly scale,both the p S and p P are very low( close to 0),far below the threshold of 0. 05 of tidal triggering of earthquakes,and the predominant tidal phase for earthquake triggering is- 18. 95°,close to the maximum 0°( new moon and full moon) of the earth tide in monthly scale. Regarding the statistical test result of tidal triggering of earthquakes,a preliminary explanation is given as to why the trigger effect in the east-west direction is greater than that in north-south direction.展开更多
基金The National Basic Research Program of China(973 program)(Grant No.2008CB425802)the Opening Fund of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection(Chengdu University of Technology)(No.SKLGP2010K007)for providing our research funding
文摘Fourier spectra and acceleration response spectra of near-field acceleration records of the 2008 Wenchuan Earthquake have been calculated.Relative fundamental frequencies(or predominant periods) were characterized.Then,the natural frequencies of a range of slopes with different geometric characteristics,such as height,slope ratio,and pattern,were analyzed.The seismic responses of the slopes were compared,and the variability of seismic response with the above geometric elements was found.Results show that if slope height increases,and provided that other conditions are unchanged,the natural frequency of the first mode of a doublesurface slope will change as a power law.However,natural frequencies will diminish(based on a parabolic function) as the slope angle becomes large.Both the surface pattern and the number of surfaces on a slope can have a great impact on the seismic response of the slope.Moreover,within a certain range of slope heights or angles,either height or angle will also greatly influence the variability of the seismic response.The results of this research will be helpful to understanding seismic dynamic response features and explaining the ways that slope stability can be affected by earthquakes.
基金The National Natural Science Foundation of China(No.51678141)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX17_0128)the Fundamental Research Funds for the Central Universities
文摘To evaluate the coupling pounding-friction effect between bridge girders and retainers and its influence on bridge seismic response, a reinforced concrete （RC） continuous bridge is selected as the research object. Three bridge finite element （FE） models were built using OpenSees, in which the longitudinal and transverse pounding elements, as well as the transverse failure element of bearings were introduced. Based on this, tire seismic response analysis considering the coupling pounding-friction effect was conducted for the continuous bridge subjected to bi-directional ground motions. Furthermore, the influential parameters were analyzed. The analysis results indicate that the coupling pounding-friction effect can alter the internal force distribution of the bridge structure and generate additional torsional force to bridge columns. The friction coefficient and longitudinal pounding gap size are two important factors. The appropriate friction coefficient and longitudinal pounding gap size can significantly reduce seismic response of girders, and effectively transfer part of the girder inertia force from the fixed columns to the sliding columns, which can reduce the seismic demands of the fixed columns and improve the seismic performance of continuous bridge structures.
文摘The basic element in any sustainable dam project is safety, which includes the following safety elements： O structural safety, dam safety monitoring, operational safety and maintenance, and emergency planning. Long-term safety primarily includes the analysis of all hazards affecting the project; that is, hazards from the natural environment, hazards from the man-made environment, and project-specific and site-specific hazards. The special features of the seismic safety of dams are discussed. Large dams were the first structures to be systematically designed against earthquakes, starting in the 1930s. How- ever, the seismic safety of older dams is unknown, as most were designed using seismic design criteria and methods of dynamic analysis that are considered obsolete today. Therefore, we need to reevaluate the seismic safety of existing dams based on current state-of-the-art practices and rehabilitate deficient dams. For large dams, a site-specific seismic hazard analysis is usually recommended. Today, large dams and the safety-relevant elements used for controlling the reservoir after a strong earthquake must be able to withstand the ground motions of a safety evaluation earthquake. The ground motion parameters can be determined either by a probabilistic or a deterministic seismic hazard analysis. During strong earthquakes, inelastic deformations may occur in a dam; therefore, the seismic analysis has to be car- ried out in the time domain. Furthermore, earthquakes create multiple seismic hazards for dams such as ground shaking, fault movements, mass movements, and others. The ground motions needed by the dam engineer are not real earthquake ground motions but models of the ground motion, which allow the safe design of dams. It must also be kept in mind that darn safety evaluations must be carried out several times during the long life of large storage dams. These features are discussed in this paper.
基金supported by the National Natural Science Foundation of China (No. 51478311)the Natural Science Foundation of Tianjin, China (No. 14JCQNJC07400)
文摘In this paper, the verticalseismic effects on tunnels are studied based on a classic mass–damper–spring model. An analyticaldiscrete modelof urban underground tunnels subjected to verticalearthquake excitations is proposed by considering the first verticalvibration mode. Taking a light railproject in Tianjin as an example, this study uses the proposed discrete modelto analyze the displacements of tunneland soilunder verticalearthquake excitations. The soildisplacement responses at different tunnellocations are analyzed with linear random vibration theory.The computationalcost is greatly reduced using the proposed model. It can be seen that different from the case of horizontalearthquakes, the displacement responses under verticalearthquake excitations keep growing after seismic acceleration reaches its peak for a short duration, and then,they begin to decay. The soils at different positions around the tunnels have large relative displacement under verticalearthquake excitations. Moreover, a finite-element modelis also established for displacement responses using ABAQUS.The comparison with the results of the finite-element modelshows that the results of the proposed discrete modelare available.
文摘Probabilistic analysis is a rational approach for engineering design because it provides more insight than traditional deterministic analysis. Probabilistic evaluation on seismic stability of three dimensional (3D) slopes is studied in this paper. The slope safety factor is computed by combining the kinematic approach of limit analysis using a three-dimensional rotational failure mechanism with the pseudo-dynamic approach. The variability of input parameters, including six pseudo-dynamic parameters and two soil shear strength parameters, are taken into account by means of Monte-Carlo Simulations (MCS) method. The influences of pseudo-dynamic input variables on the computed failure probabilities are investigated and discussed. It is shown that the obtained failure probabilities increase with the pseudo-dynamic input variables and the pseudo-dynamic approach gives more conservative failure probability estimates compared with the pseudo-static approach.
基金supported by the National Natural Science Foundation of China(No.41774059)the Sichuan Science and Technology Program(No.2018JY0005)
文摘The April 20,2013,Ms 7.0 Lushan Earthquake was a major earthquake that followed the Ms 8.0 Wenchuan Earthquake on May 12,2008.Frequent earthquakes have caused heavy casualties and property loss in Western Sichuan.Earthquake disasters are often closely related to the amplification effect of ground motion.Studying the ground motion characteristics of near-surface geological structures helps to understand the distribution of potential earthquake disasters.In this study,we investigated ground motion amplification in the downtown area of Lushan using numerical simulation and aftershock data from the Lushan Earthquake.Using the Lushan earthquake aftershock data from nine seismic stations distributed in the area,the amplification effect of the sites was determined using the"reference site spectral ratio"method.The results show that the frequency of the ground motion amplification in the area was in the range 5–10 Hz,and the corresponding amplification peak was from 3 to 14.Among the study sites,the amplification(14 times)at L07 was the most prominent.To study further the amplification characteristics,shear-wave velocity models for the structures under these sites were established using passive-source Rayleigh surfacewave exploration.One-dimensional(1 D)and two-dimensional(2 D)seismic amplification effects were simulated using horizontally propagating shear-wave modeling.Except Site L07,the 1 D simulation results of each site well reflected the variation feature of the seismic amplification on the frequency band below the observed peak frequency,although the overall simulated amplification peaks were smaller than the observed results.The 2 D simulation of the remarkable amplification phenomenon at L07 was in better agreement with the observation result than was the 1 D simulation,indicating that the seismic amplification in the Modong area is influenced by lateral variation of the Quaternary sediments.
基金Project(90815024) supported by the National Natural Science Foundation of China
文摘To find the distribution patterns of dynamic amplification coefficients for dams subjected to earthquake, 3D seismic responses of concrete-faced rockfill dams with different heights and different shapes of river valley were analyzed by using the equivalent-linear model. Statistical analysis was also made to the seismic coefficient, and an empirical formula for calculating the maximum acceleration was provided. The results indicate that under the condition of the same dam height and the same base acceleration excitations, with the increase of the river valley width, the position of the maximum acceleration on the axis of the top of the dam moves from the center to the riversides symmetrically. For the narrow valleys, the maximum acceleration occurs in the middle of the axis at the top of the dam; for wide valleys the maximum acceleration appears near the riversides. The result negates the application of 2D dynamical computation for wide valleys, and shows that for the seismic response of high concrete-faced rockfill dams, the seismic coefficient along the axis should be given, except for that along the dam height. Seismic stability analysis of rockfill dams using pseudo-static method can be modified according to the formula.
文摘Using the four phases (1996～1999) of re-surveying data from the GPS network along the Shanxi fault zone, the recent state of horizontal movement of the fault zone and its relation with the Datong-Yanggao M5.6 earthquake (November 1, 1999), which took place on the north end of the monitored area, are analyzed. In the focal region, three areas with relatively higher strain (1×10 -6) appeared in Xinzhou and to the northeast of Jiexiu. The Shanxi fault zone is mainly controlled by the WNW-ESE-trending compressive stress field and the NNE-SSW-trending tensile stress field, and it does not have strike-slip movement. When examined for long-term tendency, attention should be paid to the junctures between the three moving elements.
基金Projects(51908557,51378510)supported by the National Natural Science Foundation of China。
文摘A method combining the pseudo-dynamic approach and discretization technique is carried out for computing the active earth pressure.Instead of using a presupposed failure mechanism,discretization technique is introduced to generate the potential failure surface,which is applicable to the case that soil strength parameters have spatial variability.For the purpose of analyzing the effect of earthquake,pseudo-dynamic approach is adopted to introduce the seismic forces,which can take into account the dynamic properties of seismic acceleration.A new type of micro-element is used to calculate the rate of work of external forces and the rate of internal energy dissipation.The analytical expression of seismic active earth pressure coefficient is deduced in the light of upper bound theorem and the corresponding upper bound solutions are obtained through numerical optimization.The method is validated by comparing the results of this paper with those reported in literatures.The parametric analysis is finally presented to further expound the effect of diverse parameters on active earth pressure under non-uniform soil.
文摘This paper is dedicated to the study of the seismic performance of an existing RC （reinforced concrete） bridge localized in a region of moderate seismicity. The bridge has six spans and piers with very different heights, three of which are monolithically connected to the deck. To understand the roles of the different pier sizes in the overall behavior, several analyses were carried out in the longitudinal direction： （1） linear dynamic approach; （2） non-linear static approach; （3） non-linear dynamic approach. Linear dynamic analysis was made in order to design the bridge for the ultimate limit state considering the largest value of the ductility factor. No safety verification was made for the other loads. Using non-linear static analyses, sensitivity was performed to check the influence of reinforcement quantities of each pier on the overall behavior of the bridge under Lisbon seismic action. For the non-linear dynamic approach, a series of strong motion records compatible with the EC-8 spectrum for Lisbon area were generated. The very same combinations of reinforcement quantities were studied. Comparisons between static and dynamic non-linear analysis were made to confirm the validity of the first one in the case under analysis, where the period of vibration is quite high.
基金sponsored by the Earthquake Situation Tracking Task of 2013(2013020119)the Fund of Earthquake Administration of Xinjiang Uygur Autonomous Region,China(201304)
文摘A statistical analysis on earthquake activity in the Kashi-Wuqia intersection area triggered by earth tide is done by Schusters test and the Permutation test on daily and monthly scales. The north-south,east-west component of the tidal force and tidal body stress are chosen as the tidal curve in the daily scale. The results show that most of the earthquakes occurred near the maximum 0° of the three kinds of tidal curves,the predominant tidal phases of the earthquake are- 5. 86°,6. 60° and- 15. 52°,and the frequency of the earthquakes increases with the increase of the tide; with three kinds of tidal curves( the north-south,east-west component of the tidal force and tidal body stress),the p S of Schusters test for all the earthquakes is 10. 52%,2. 40% and 2. 06%,and the p P of the Permutation test is 10. 90%,2. 40% and 2. 06%,and the results of p S and p P based on the east-west component of the tidal force and tidal body stress are below the threshold of 0. 05 that tidal triggering of earthquakes. In the monthly scale,both the p S and p P are very low( close to 0),far below the threshold of 0. 05 of tidal triggering of earthquakes,and the predominant tidal phase for earthquake triggering is- 18. 95°,close to the maximum 0°( new moon and full moon) of the earth tide in monthly scale. Regarding the statistical test result of tidal triggering of earthquakes,a preliminary explanation is given as to why the trigger effect in the east-west direction is greater than that in north-south direction.
