RELIABILITY BASED ANALYSIS ON RESERVOIR INDUCED EARTHQUAKES

Reservoir induced earthquakes (RIE) are caused by impoundment of reservoir,with the characteristics of small magnitude and shallow focal depth,but they can also lead to not only economic loss,but also many serious secondary disasters,such as dam destruction,landslide,producing greater damages far more than the damages directly produced by earthquakes.So study on RIE is quite significant in the field of dam construction,thus more attentions should be paid to RIE.There are many factors to induce reservoir earthquakes,such as geological condition,rock mass mechanical index,state of crustal stress,pore pressure distribution,all of which are extremely difficult to measure due to the presence of many randomness;even if applying most advanced methods to measure them,the values fluctuate in great range,without a certain value in time and space.The great variety of these parameters gives rise to troubles to analyze RIE by deterministic approaches.How to handle the randomness of these factors has become vital problem in the field of RIE research.In this study,based on probability theory,and taking the main influence factors as stochastic variables,a new method to analyze probability of RIE was proposed by applying reliability theory.Firstly,the factors inducing reservoir earthquakes were analyzed,of which pore pressure in fault caused by water impounding of reservoir plays a vital role in triggering earthquakes.Then,taking these factors,including attitude,friction coefficient,cohesion of fault plane,stress state of fault plane and pore pressure in fault,as stochastic variables,performance function of triggering earthquakes was established by applying Coulomb stress on the fault plane,and reliability theory was used to analyze probability of earthquake induced by main factors.A special case analysis showed that:(1) The probability of induced earthquakes dramatically increases as pore pressure in fault increases;under the condition of equal pore pressure at triggering earthquakes area,probability of induced earthquakes obviously rises with enlarging of variation of pore pressure;(2) those faults with strike approximately parallel to horizontal maximum principal stress direction or with steep dip angle about more than 60° are prone to inducing earthquake;(3) as horizontal minimum principal stress increases,which has greater effect on induced earthquakes than horizontal maximum principal stress,probability of induced earthquakes becomes lower and fault keeps in more stable condition;(4) probability of induced earthquakes gradually decreases with the increase of friction coefficient and cohesion of fault plane;However,the effect of friction coefficient on induced earthquakes is much greater than the cohesion of fault plane.     

Preliminary analysis on the tectonic stress level in the source region of Tangshan earthquake

Introduction Analyzing tectonic stress field based on focal mechanism data is an important way to the study tectonic evolvement of lithosphere and associated dynamic process. Such studies growrapidly in China and abroad (Zoback, 1992; Plenefisch, Bonjer, 1997; XU, 1985; CUI, XIE, 1999). At present most of the studies focus on the inversion of focal mechanism data for the direction and relative magnitude of stress tensor, and few on absolute stress. Using focal mechanism and fault scratch,…     

盈江地区构造应力场和断层识别的联合迭代式反演研究

搜集了盈江及其邻区5组地震序列震源机制解并反演得到该区域的构造应力场。研究结果显示：盈江地区整体主压应力以NNE向为主,主张应力以ESE向为主;但其局部应力场不完全一致,沿苏典断裂分布的主压应力轴走向随着断裂走向由北向南延伸角度逐渐向北偏移,而盈江地区的西南部,其主压应力走向更偏向于东,这可能与大盈江断裂的横向拉伸有关。此外,本研究通过应力场反演识别出了5组地震序列震源机制解的主发震断层节面的走向、倾角、滑动角及发震断层的摩擦系数,为今后该区域的地震研究及地壳动力学变迁提供了参考。     

青海共和盆地地应力状态与断层稳定性分析

青海共和盆地地质构造条件复杂,断层十分发育,区域内既有地热、太阳能、矿产等资源丰富,存在龙羊峡水库诱发地震环境背景.因此,分析青海共和盆地地应力特征与地质结构易滑性对于青海东部地区防震减灾具有重要意义.对盆地及附近区域内19个钻孔、65条水压致裂数据和44条应力解除实测数据进行统计分析,并基于断层摩擦强度理论、Byer...     

THE GEOLOGICAL AND ROCK MECHANICAL DISTINCTION EVIDENCE BETWEEN STICK-SLIP AND CREEP IN HOST ROCK SEGMENTS OF FAULT

Paleo-seismic and fault activity are hard to distinguish in host rock areas compared with soft sedimentary segments of fault. However, fault frictional experiments could obtain the conditions of stable and unstable slide, as well as the microstructures of fault gouge, which offer some identification marks between stick-slip and creep of fault. We summarized geological and rock mechanical distinction evidence between stick-slip and creep in host rock segments of fault, and analyzed the physical mechanisms which controlled the behavior of stick-slip and creep. The chemical composition of fault gouge is most important to control stick-slip and creep. Gouge composed by weak minerals, such as clay mineral, has velocity weakening behavior, which causes stable slide of fault. Gouge with rock-forming minerals, such as calcite, quartz, feldspar, pyroxene, has stick-slip behavior under condition of focal depth. To the gouge with same chemical composition, the deformation mechanism controls the frictional slip. It is essential condition to stick slip for brittle fracture companied by dilatation, but creep is controlled by compaction and cataclasis as well as ductile shear with foliation and small fold. However, under fluid conditions, pressure solution which healed the fractures and caused strength recovery of fault, is the original reason of unstable slide, and also resulted in locking of fault with high pore pressure in core of fault zone. Contrast with that, rock-forming minerals altered to phyllosilicates in the gouges by fluid flow through degenerative reaction and hydrolysis reaction, which produced low friction fault and transformations to creep. The creep process progressively developed several wide shear zones including of R, Y, T, P shear plane that comprise gouge zones embedded into wide damage zones, which caused small earthquake distributed along wide fault zones with focal mechanism covered by normal fault, strike-slip fault and reverse fault. However, the stick-slip produced mirror-like slide surfaces with very narrow gouges along R shear plane and Y shear plane, which caused small earthquake distributed along narrow fault zones with single kind of focal mechanism.     

2009年云南姚安6.0级地震震源机制与发震构造的分析研究

利用P波、SV波、SH波初动及其振幅比联合反演震源机制解的方法,计算了2009年7月9日发生在云南姚安6.0级地震余震序列的震源机制解,同时结合地震序列的空间分布,对姚安6.0级地震的发震断层性质和震区应力场特征进行综合分析。结果分析表明：（1）姚安6.0级地震发震断层为NWW—SEE向的直立右旋走滑断层,与美国哈佛大学的主震CMT解节面基本一致,也与余震优势方向分布一致,证明结果可靠;（2）震区主压应力场优势方向为NNW—SSE向,与其现今区域构造应力场主压应力NNW—SSE向一致,表明主震应力场主要受到现今区域构造应力场的控制,同时还有一些小的余震与主震应力场不同,表明震区应力场的多样性和复杂性;（3）结合本次地震序列的空间分布、震源机制解特征、震区断裂构造特征综合分析,综合判定姚安6.0级地震的发震构造属于马尾箐断裂。     

2017年精河MS6.6地震邻区构造应力场特征与发震断层性质的厘定

2017年8月9日新疆精河发生M_S6.6地震,深入了解该地震的构造应力背景及其所破裂断层的活动特性对理解其孕震过程及震后的地震危险性估计十分重要.本研究自GCMT目录收集了2017年8月9日新疆精河M_S6.6地震震中及其邻区的253个震源机制解,应用MSATSI软件反演了该地震及其邻区的应力场.反演结果显示,西北区域应力场的最大主压应力轴的方位从西到东呈现出NNW-NS-NNE的渐变过程,东南区域应力场最大主压应力轴的方位稳定于NNE向,倾角都较小;最大主张应力轴都基本沿东西向,倾角相对较大;西北区域较大的R值显示出区域应力场主要受近NS向水平挤压作用,中部挤压分量相对较大,西部和东部挤压分量相对较小.根据所反演的区域构造应力场,结合发震的库松木契克山前断裂的地质调查参数,估算该断裂的理论滑动角为137.7°,误差为21.3°,验证了地质上得到的库松木契克山前断裂的逆冲兼右旋走滑性质.判断该断裂滑动性质的另一种方法是通过发生在该断裂上地震的震源机制验证.本研究首先计算了发生在库松木契克山前断裂不同机构给出的震源机制节面在所反演的局部应力场作用下的理论滑动角,发现理论滑动角与实际地震震源机制滑动角相差很小,验证了反演的局部应力场的正确性;而后计算了局部应力场作用下的库松木契克山前断裂上的理论震源机制与实际发生地震震源机制的三维空间旋转角,发现两者在给定的误差范围内是一致的.本研究自地球物理角度确证了库松木契克山前断裂的滑动性质,为该地区的地震孕育环境、地震活动性和地球动力学研究提供了基础.     

STUDY ON THE SEISMOGENIC FAULT AND DYNAMICS PARAME-TERS OF THE 2014 MS6.6 JINGGU EARTHQUAKE IN YUNNAN

On October 17, 2014, a M_S6.6 earthquake occurred in Jinggu, Yunnan. The epicenter was located in the western branch of Wuliang Mountain, the northwest extension line of Puwen Fault. There are 2 faults in the surrounding area, one is a sinistral strike-slip and the other is the dextral. Two faults have mutual intersection with conjugate joints property to form a checkerboard faulting structure. The structure of the area of the focal region is complex. The present-day tectonic movement is strong, and the aftershock distribution indicates the faulting surface trending NNW. There is no obvious surface rupture related to the known fault in the epicenter, and there is a certain distance from the surface of the Puwen fault zone. Regional seismic activity is strong. In 1941, there were two over magnitude 7.0 earthquakes in the south of the epicenter of Jinggu County and Mengzhe Town. In 1988, two mainshock-aftershock type earthquakes occurred in Canglan-Gengma Counties, the principal stress axes of the whole seismic area is in the direction of NNE. Geological method can be adopted to clarify the distribution of surficial fracture caused by active faults, and high-precision seismic positioning and spatial distribution characteristics of seismic sequences can contribute to understand deep seismogenic faults and geometric features. Thus, we can better analyze the three-dimensional spatial distribution characteristics of seismotectonics and the deep and shallow tectonic relationship. The focal mechanism reveals the property and faulting process to a certain extent, which can help us understand not only the active property of faults, but also the important basis for deep tectonic stress and seismogenic mechanism. In order to study the fault characteristic of the Jinggu earthquake, the stress field characteristics of the source area and the geometric parameters of the fault plane, this paper firstly uses the 15 days aftershock data of the Jingsuo M_S6.6 earthquake, to precisely locate the main shock and aftershock sequences using double-difference location method. The results show that the aftershock sequences have clustering characteristics along the NW direction, with a depth mainly of 5~15km. Based on the precise location, calculations are made to the focal mechanisms of a total of 46 earthquakes including the main shock and aftershocks with M_L ≥ 3.0 of the Jinggu earthquake. The double-couple(DC)component of the focal mechanism of the main shock shows that nodal plane Ⅰ:The strike is 239°, the dip 81°, and the rake -22°; nodal plane Ⅱ, the strike is 333°, the dip 68°, and the rake -170.31°. According to focal mechanism solutions, there are 42 earthquakes with a focal mechanism of strike-slip type, accounting for 91.3%. According to the distribution of the aftershock sequence, it can be inferred that the nodal plane Ⅱ is the seismogenic fault. The obtained focal mechanism is used to invert the stress field in the source region. The distribution of horizontal maximum principal stress orienation is concentrated. The main features of the regional tectonic stress field are under the NNE-SSW compression(P axis)and the NW-SE extension(T axis)and are also affected by NNW direction stress fields in the central region of Yunnan, which indicates that Jinggu earthquake fault, like Gengma earthquake, is a new NW-trending fault which is under domination of large-scale tectonic stress and effected by local tectonic stress environment. In order to define more accurately the occurrence of the fault plane of the Jinggu earthquake, with the precise location results and the stress field in the source region, the global optimal solution of the fault plane parameters and its error are obtained by using both global searching simulated annealing algorithm and local searching Gauss-Newton method. Since the parameters of the fault plane fitting process use the stress parameters obtained by the focal mechanism inversion, the data obtained by the fault plane fitting is more representative of the rupture plane, that is, the strike 332.75°, the dip 89.53°, and the rake -167.12°. The buried depth of the rupture plane is 2.746km, indicating that the source fault has not cut through the surface. Based on the stress field characteristics and the inversion results of the fault plane, it is preliminarily believed that the seismogenic structure of the Jinggu earthquake is a newly generated nearly vertical right-lateral strike-slip fault with normal component. The rupture plane length is about 17.2km, which does not extend to the Puwen fault zone. Jinggu earthquake occurred in Simao-Puer seismic region in the south of Sichuan-Yunnan plate. Its focal mechanism solution is similar to that of the three sub-events of the Gengma earthquake in November 1988. The seismogenic structure of both of them is NW-trending and the principal stress is NE-SW. The rupture plane of the Jinggu main shock(NW direction)is significantly different from the known near NS direction Lancang Fault and the near NE direction Jinggu Fault in the study area. It is preliminarily inferred that the seismogenic structure of this earthquake has a neogenetic feature.     

昌马地震应力场及发震机制研究

本文利用前人大量的地质、地球物理资料，建立了昌马盆地的立体地质模型，利用三维有限元法研究了１９３２年昌马７．６级地震前后应力场的变化及其昌马地震成因机制，结果表明：（１）震源断层走向与利用主压应力推测的断裂走向相差６５°，可能是由于地壳浅部旋转的主压应力与深部北东方向的主压应力所产生的力矩使块体发生旋转所致，其枢纽点即为震源所在；同时，该旋转也导致了地震断层和震源断层在力学性质和几何性质上的不同。（２）昌马地震是在闭锁、贯通和块体旋转联合作用下形成的。（３）区域应力场与局部应力场不一致、应力松弛单元的出现可能与地震的孕育、发生有关。（４）断裂活动的不均一性与平面最大剪应力分布不均匀成正相关，且各断裂均以相对左旋走滑兼挤压为特征，但是其走滑量的分布是不均匀的。     

长宁地区复杂地震活动的力学成因分析

长宁地区地震活动复杂,发生在长宁背斜轴部的长宁Ms6.0地震及其后续中强余震的震源机制与相距仅十几公里的南部向斜区内的中强震具有显著差异;这种差异仅仅是由于发震断层构造不同所造成的,还是孕育地震的应力场本身也存在局部变化?为了回答这一问题,本文在通过双差层析成像反演修正小震定位和波速结构的基础上,利用小震综合震源机制解...     

乌鲁木齐地区现今构造应力场综合分析

乌鲁木齐地处天山中段.震源机制解研究表明,北天山中段区域主压应力方向为N10°E左右,且具有自西向东逐渐东偏的特点.在乌鲁木齐地区,由中强地震震源机制解反演的主压应力方向为N15°-20°E;由断层滑动资料反演的乌鲁木齐周边构造应力场的主压应力方向为N17°W-N2°E.上述两种资料反演的乌鲁木齐构造应力场主压应力方向...     

CHARACTERISTICS OF FOCAL MECHANISMS AND STRESS FIELD OF YUNNAN AREA

Using the seismic waveform data recorded by regional seismic network of Yunnan and Sichuan and the method of CAP, we calculate and obtain the focal mechanism of 268 earthquakes with the magnitude of M_L≥4.0 occurring in Yunnan during Jan. 1999 to Aug. 2014; then, we analyze the types and the regional feature of the focal mechanism of earthquakes in Yunnan, on the basis of the focal mechanism of 109 earthquakes analyzed by Harvard University. Based on the data of the above focal mechanism solutions, we adopt the method of damped regional-scale stress inversion to calculate the best-fitting tectonic stress tensor of every grid in Yunnan; and adopt the method of maximum principal stress to calculate the direction of maximum horizontal principal stress in Yunnan. The result shows that: (1)the strike-slip type is the most principal type of the earthquake focus in the study area and the second is the normal faulting type; while, the reverse-fault type is relatively small. The spatial distribution of focal mechanism is obvious. This reflects that the dynamic source and acting force are different in different parts of the study area. (2)The direction of the stress field in Yunnan shows a certain spatial continuity. Maximum horizontal principal compressive stress is mainly clockwise from north to south and counterclockwise from the west to the east. The direction of stress field shows inhomogeneity in space. There exist two stress conversion zones respectively in EW and NS direction. The inversion result of stress field shows that the stress field in Yunnan is complex and the principal stress direction changes greatly; and there are obvious differences in different regions.     

CHARACTERISTICS OF TECTONIC STRESS FIELD OF THE XIAOWAN RESERVOIR BEFORE AND AFTER THE IMPOUNDMENT

Using the seismic waveform data of Xiaowan seismic network and Yunnan seismic network, we determined the focal mechanisms of 36 earthquakes(M_L ≥ 3.0)from Jun. 2005 to Dec. 2008 and 51 earthquakes(M_L ≥ 2.5)from Jan. 2009 to Dec. 2015 by generalized polarity and amplitude technique. We inverted tectonic stress field of the Xiaowan reservoir before impounding, using the focal mechanisms of 36 earthquakes(M_L ≥ 3.0)from Jun. 2005 to Dec. 2008 and CAP solutions of 58 earthquakes(M_L ≥ 4.0)collected and the solutions in the Global Centroid Moment Tensor(GCMT)catalog; We inverted local stress field of the reservoir-triggered earthquake clustering area, using 51 earthquakes(M_L ≥ 2.5)from Jan. 2009 to Dec. 2015. Focal mechanisms statistics show that, the Weixi-Qiaohou Fault is the seismic fault. Focal mechanisms were strike-slip type in initial stage, but normal fault type in later stage. Focal depths statistics of 51 earthquakes(M_L ≥ 2.5)show that, the average value of focal depths in period Ⅰ, period Ⅱ and period Ⅲ are 8.2km, 7.3km and 7.8km respectively and the standard deviations are 4.3km, 3.5km and 6.0km respectively. The average value of focal depths is basically stable in different period, only the standard deviation is slightly different. Therefore, there is not positive connection between focal depth and deviation of focal mechanisms. What's more, there are 2 earthquakes(number 46 and number 47 in Fig.5 and Table 3)with almost the same magnitude, epicenter and focal depth, but they have different faulting types as normal and strike-slip. The focal mechanism of event No.46 is strike:302°, dip:40° and rake:-97° for plane Ⅰ, however, the focal mechanism of event No.47 is strike:292°, dip:82° and rake:140° for plane Ⅰ. Likewise, earthquake of number 3 and number 18 have similar characteristic. Therefore, the obvious focal mechanism difference of similar earthquake pair indicates the complexity of Weixi-Qiaohou Fault. Considering the quiet-active character of reservoir-triggered earthquakes, we discussed the change of local stress field in different period. The σ₁ of tectonic stress field was in the near-south direction, with a dip angle of 14° before the impoundment, however, the direction of σ₁ of local stress field changed continuously, with the dip angle getting larger after the impoundment. The direction of σ₁ of local stress field of reservoir-triggered earthquake clustering area is close to the strike of Weixi-Qiaohou Fault, and reservoir impoundment increased the shear stress in the fault, so the weakening of fault was beneficial to trigger earthquakes. Comprehensive analysis suggests that fluid permeation and pore pressure diffusion caused by the water impounding, and the weakening of fault caused by local stress field are the key factors to trigger earthquake in the Xiaowan reservoir.     

The stress field in Australia from composite fault plane solutions of the strongest earthquakes in the continent

The purpose of this study is to make an estimate of the stress field in the Australian continent from composite fault plane solutions of the strongest events in the area. 21 seismic events with magnitude greater than 5.0 have been chosen from a database of 400 Australian earthquakes since 1902 for performing composite fault plane solutions. The choice is based on the availability of data for first P-wave arrivals. Using data from ISC bulletins we have calculated composite fault plane solutions for six major earthquake zones in the country. An individual fault plane solution for at least one event in each zone has been computed, too. The space distribution of the focal mechanisms confirms a dominant east-west compression stress in the continent, with different tilt in different areas. The main compression axes in the Tennant Creek area (Northern Australia) are with clear north-south direction. The general direction of the plate motion is north-northeast.     

山西地区的地壳应力场

根据近20年山西地区的震源机制结果,得出了山西地壳应力场存在着有别于华北应力场的局部小区域应力场,这种小区域应力场在中部断陷盆地都是以北西—北北西向的水平拉张作用为主,而在东、西两侧隆起区则是以水平挤压作用为主的结论.但如果把上述断层面解中的所有P轴、T轴再分别投影到吴尔夫网上,得到是一个一致性很好的断层面解,由此推断山西地区的平均应力场的主要特征与华北应力场的基本特征完全相同,而山西局部小区域应力场的特征随之消失.     

FOCAL MECHANISM SOLUTIONS AND STRESS FIELD OF THE 2019 CHANGNING,SICHUAN MAINSHOCK AND ITS MODERATE-STRONG AFTERSHOCKS(MS≥4.0)

A M_S6.0 earthquake with shallow focal depth of 16km struck Changning County, Yibin City, Sichuan Province at 22:55: 43(Beijing Time)on 17 June 2019. Although the magnitude of the earthquake is moderate, it caused heavy casualties and property losses to Changning County and its surrounding areas. In the following week, a series of aftershocks with M_S≥4.0 occurred in the epicentral area successively. In order to better understand and analyze the seismotectonic structure and generation mechanism of these earthquakes, in this paper, absolute earthquake location by HYPOINVERSE 2000 method is conducted to relocate the main shock of M_S6.0 in Changning using the seismic phase observation data provided by Sichuan Earthquake Administration, and focal mechanism solutions for Changning M_S6.0 main shock and M_S≥4.0 aftershocks are inferred using the gCAP method with the local and regional broadband station waveforms recorded by the regional seismic networks of Sichuan Province, Yunnan Province, Chongqing Municipality, and Guizhou Province. The absolute relocation results show that the epicenter of the main shock is located at 28.35°N, 104.88°E, and it occurred at an unusual shallow depth about only 6.98km, which could be one of the most significant reasons for the heavier damage in the Changning and adjoining areas. The focal plane solution of the Changning M_S6.0 earthquake indicates that the main shock occurred at a thrust fault with a left-lateral strike-slip component. The full moment tensor solution provided by gCAP shows that it contains a certain percentage of non-double couple components. After the occurrence of the main shock, a series of medium and strong aftershocks with M_S≥4.0 occurred continuously along the northwestern direction, the fault plane solutions for those aftershocks show mostly strike-slip and thrust fault-type. It is found that the mode of focal mechanism has an obvious characteristic of segmentation in space, which reflects the complexity of the dislocation process of the seismogenic fault. It also shows that the Changning earthquake sequences occurred in the shallow part of the upper crust. Combining with the results from the seismic sounding profile in Changning anticline, which is the main structure in the focal area, this study finds that the existence of several steep secondary faults in the core of Changning anticline is an important reason for the diversity of focal mechanism of aftershock sequences. The characteristics of regional stress field is estimated using the STRESSINVERSE method by the information of focal mechanism solutions from our study, and the results show that the Changning area is subject to a NEE oriented maximum principal stress field with a very shallow dipping and near-vertical minimum principal stress, which is not associated with the results derived from other stress indicators. Compared with the direction of the maximum principal compressive stress axis in the whole region, the direction of the stress field in the focal area rotates from the NWW direction to the NEE direction. The Changning M_S6.0 earthquake locates in the area with complex geological structure, where there are a large number of small staggered fault zones with unstable geological structure. Combining with the direction of aftershocks distribution in Changning area, we infer that the Changning M_S6.0 earthquake is generated by rupturing of the pre-existing fault in the Changning anticline under the action of the overall large stress field, and the seismogenic fault is a high dip-angle thrust fault with left-lateral strike-slip component, trending NW.     

Visco-elastic stress triggering model of Tangshan earthquake sequence

We calculated the Coulomb failure stress change generated by the 1976 Tangshan earthquake that is projected onto the fault planes and slip directions of large subsequent aftershocks.Results of previous studies on the seismic fail-ure distribution,crustal velocity and viscosity structures of the Tangshan earthquake are used as model constraints.Effects of the local pore fluid pressure and impact of soft medium near the fault are also considered.Our result shows that the subsequent Luanxian and Ninghe earthquakes occurred in the regions with a positive Coulomb fail-ure stress produced by the Tangshan earthquake.To study the triggering effect of the Tangshan,Luanxian,and Ninghe earthquakes on the follow-up small earthquakes,we first evaluate the possible focal mechanisms of small earthquakes according to the regional stress field and co-seismic slip distributions derived from previous studies,assuming the amplitude of regional tectonic stress as 10 MPa.By projecting the stress changes generated by the above three earthquakes onto the possible fault planes and slip directions of small earthquakes,we find that the "butterfly" distribution pattern of increased Coulomb failure stress is consistent with the spatial distribution of follow-up earthquakes,and 95% of the aftershocks occurred in regions where Coulomb failure stresses increase,indicating that the former large earthquakes modulated occurrences of follow-up earthquakes in the Tangshan earthquake sequence.This result has some significance in rapid assessment of aftershock hazard after a large earthquake.If detailed failure distribution,seismogenic fault in the focal area and their slip features can be rapidly determined after a large earthquake,our algorithm can be used to predict the locations of large aftershocks.     

Recent tectonic stress field research in Shanxi graben system

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由地震释放的地震矩叠加推导平均应力场

文中给出了根据地震释放的总地震矩求解平均应力场的方法,并使用加入随机误差的人工合成震源机制解数据和唐山余震区震源机制解数据对其进行检验。由检验结果可知,该方法可以应用于区域平均应力场的求解。使用的震源机制解资料越多,所得结果越稳定,且更接近真实的区域应力场。该方法的优点是: 用每个地震的震级作为权重,能够较好地反映出大小地震在应力场反演中的不同贡献; 并且在计算过程中不需要知道震源机制解2个节面中哪个节面为地震断层面。     

Determinations of directions of the mean stress field in Sichuan-Yunnan region from a number of focal mechanism solutions

Introduction With the model of double couple point source, both orientations of the T, B, and P axes of a single focal mechanism solution and parameters of the two nodal planes may be determined. The focal mechanism solution under ″the model of the best double couple″ can also be given by seis- mic moment tensor, such as those provided by Harvard CMT solutions. The orientations of the T, B, and P axes from one earthquake are associated with the released stress, but they cannot be re- gar…