THE STATIC STRESS TRIGGERING INFLUENCES OF THE 2015 MW6.4 PISHAN,XINJIANG EARTHQUAKE ON THE NEIGHBORING AREAS

Based on the rupture models of the 2015 Pishan M_W6.4 earthquake and half space homogeneous elastic model, the Coulomb stress changes generated by the earthquake are calculated on the active faults near the earthquake region. The horizontal stress changes and the displacement field are estimated on the area around the epicenter. Results show that:(1)The Coulomb stress is decreased in the west of the western Kunlun frontal thrust fault(9.5×10³Pa), and increased in the east of the western Kunlun frontal thrust fault and the middle of the Kangxiwa faults. More attention should be taken to the seismic rick of the east of the western Kunlun frontal thrust fault; (2)Based on the analysis on the location of the aftershocks, it is found that most of the aftershocks are triggered by the earthquake. In the region of increased Coulomb attraction, the aftershock distribution is more intensive, and in the area of the Coulomb stress reduction, the distribution of aftershocks is relatively sparse; (3)The horizontal area stress increases in the north and south of the earthquake(most part of the Qaidam Basin and the northwest of the Qinghai-Tibet plateau), and decreases in the east and west of the earthquake(northern part of the Qinghai-Tibet plateau and eastern part of the Pamir Mountains). In the epicenter area, the principal compressive stress presents nearly NS direction and the principal extensional stress presents nearly EW direction. The principal compressive stress shows an outward radiation pattern centered on the epicenter with the principal extensional stress along the direction of concentric circles. The principal compressive stress presents NW direction to the west of the epicenter, and NE to the east of the epicenter. With the increase of radius, the stress level gradually decays with 10⁷Pa in the epicenter and hundreds Pa in the Maidan Fault which is in the north of the Qaidam Basin.     

THE COSEISMIC SOURCE SLIP AND COULOMB STRESS TRIGGERING OF 2015 NEPAL GORKHA MW7.9 AND KODARIMW7.3 EARTHQUAKE BASED ON InSAR MEASUREMENTS

According to the structure of the Himalayan orogenic belt, a low-angle antilistric thrust-slip fault model is used to simulate the ramp on the rupture portion of the Main Himalayan Fault. Based on descending Alos -2 and Sentinal -1 data, we invert for the coseismic slip models of the Gorkha earthquake and its largest aftershock, Kodari earthquake. In contrast to the inversion using Alos -2 or Sentinal -1 separately, the joint inversion of both data sets has stronger constraint for the deep slip and can obtain more details in Gorkha earthquake. The rupture depth obtained by joint inversion can be as deep as 24km underground, cutting across the locking line to the transition of locked and the creeping zone. The largest slip is as large as 4.5m appearing 17km underground and the dip angle is between 3°and 10°. Gorkha and Kodari earthquakes have the similar focal mechanisms, both of which are mainly thrusting, and yet some right-lateral slip component in Gorkha earthquake. The inversion results reveal that slip models of the Nepal mainshock and its largest aftershock are complementary in space and the Kodari earthquake occurs in the gaps of slip in Gorkha earthquake. The epicenter of the Kodari earthquake is just right in the transitive zone of the positive and negative Coulomb stress change, where the Coulomb stress change can reach 0.4MPa. We thus argue that Kodari earthquake has been triggered by the Gorkha earthquake.     

CONSTRAINING THE FOCAL MECHANISM OF THE 2015 NEPAL EARTHQUAKE WITH OBSERVATIONS OF THE CONTINUOUS GRAVITY STATIONS

On 25 April 2015, a magnitude M_S8.1 interplate thrust earthquake ruptured a densely instrumented region of Nepal. After earthquake, the focal mechanism solutions of Nepal earthquake were provided by well-respected international earthquake research institutions based on different data and methods, which were different. We compared free oscillations observed by 18 spring gravimeters of continuous gravity stations with synthetic normal modes corresponding to 3 different focal mechanisms for the Nepal earthquake, and the focal mechanisms solutions of Nepal earthquake were analyzed and constrained by spherical normal modes in a 2 to 5mHz frequency band. Based on the optimal focal mechanism, the accurate magnitude was searched. The results show that the focal mechanism of Nepal earthquake can be estimated by spherical modes in the 2 to 5mHz frequency band. The synthetic modes corresponding to the focal mechanism determined by the GCMT Moment Tensor Solution showed agreement to the observed modes, the average of misfit factors F was 0.03, and the average of scaling factors was 1.04, which was closest to 1, suggesting that earthquake magnitudes predicted in this way can reflect the total energy released by the earthquake. Based on the focal mechanism solutions provided by GCMT, keeping the strike, dip, slip, depth constant, adjusting the scalar moment, the real scalar moment was searched. When the average of scaling factors was 1, the average of misfit factors F was only 0.03. After calculation, the scalar moment of Nepal earthquake was 8.09×10²⁰ Nm, and the corresponding magnitude was M_W7.91.     

THE DISPLACEMENT AND STRESS FIELD GENERATED BY THE COLLAPSE IN PINGYI COUNTY,SHANGDONG PROVINCE,ON DECEMBER 25, 2015

A collapse happened in Pingyi County, Shandong Province, on December 25, 2015. The displacement field, stress field and Coulomb failure stress change on the Mengshan frontal fault generated by the collapse are calculated by using point collapse model in isotropic medium. The result shows that: (1) The maximum horizontal displacement is located at the center of the collapse with value of~18mm. The horizontal displacements are greater than 1mm within~5km of the collapse with its direction pointing to the collapse center. The maximum subsidence is located at the center of the collapse with the value of 4mm. The subsidence is greater than 1mm within ~3km of the collapse. The displacement field decays so rapidly that can be ignored at far away from the collapse for the shallow source, which caused local displacement field. (2) Influenced by the free surface, the contraction area stress within ~5km of the collapse with the order of 1000Pa and expansion area stress in farther away areas at depth of 2km are estimated. the expansion area stress of 1000Pa is estimated at the~5km from the collapse center. Then the expansion area stress decays to 100Pa at the distance of ~10km from the collapse. The maximum compressive and extensional principal stresses are estimated as 10000Pa at the depth of 2km. The compressive stress axes present radical direction pointing to the collapse within ~5km of the center. In farther away from the collapse, The extensional principal stress axes present radical direction pointing to the center of the collapse. With farther distance to the collapse, the compressive and extensional stress decay rapidly to the order of 100Pa. (3) The Coulomb failure stress on the northwestern part of the Mengshan frontal fault, which is known as active segment of the Mengshan frontal fault, is decreased by the collapse with maximum value of 2500Pa. Whereas, the Coulomb failure stress on the southeastern part of the Mengshan frontal fault, which is known as left-lateral normal slip fault segment in Quaternary period, is increased by the collapse with maximum of 2400Pa, to which attention would be paid in seismic hazard analysis.     

2015年尼泊尔强震序列对中国大陆的应力影响

基于2015年尼泊尔地震序列的破裂模型及均匀弹性半空间模型,计算了该地震序列传递到中国西藏境内发生在定日县地震和聂拉木县地震的应力.2015年尼泊尔地震序列导致定日县地震和聂拉木地震节面和滑动方向的库仑应力增加(2~3)×103 Pa和(2.4~3.1)×105 Pa, 表明这两个地震受到尼泊尔地震序列的触发.其次,我们计算了2015年尼泊尔地震序列在中国大陆及其附近主要活动断层上产生的库仑应力变化.喜马拉雅主山前逆冲断裂和青藏高原内部的拉张正断层上的库仑应力有较大的增加,而青藏高原的走滑断裂,如阿尔金断裂、东昆仑断裂、玉树玛曲断裂、班公错断裂西部、嘉黎断裂的库仑应力有较大的降低.天山南北两侧的断裂库仑应力降低.而华北及东北、华南地区的库仑应力变化几乎可以忽略不计.最后,计算了该地震序列造成的水平应力变化.水平面应力在2015年尼泊尔地震序列北向(青藏高原大部和新疆区域)增加(拉张),而在地震序列东侧的西藏南部和川滇地区南部降低(压缩),在华北和东北仅有少许增加,在华南地区有少许降低.在中国西部,主压应力表现为以2015年地震序列为圆心的向外辐射状,而主张应力方向与同心圆切线方向大体一致.水平主压应力方向在东北地区为北东向,在华北地区为北东东向,在华南地区为南东东向.这种模式与现今构造应力场方向相似,表现了2015尼泊尔地震序列所代表的印度板块和欧亚板块的碰撞是中国大陆构造变形的主要动力来源.     

汶川地震白沙河段最大地表水平位移量的成因分析

最大同震位移量是活动构造研究、断层活动特性判定和地震危险性分析的一个重要参数,它关系到地震危险区最大震级、地震复发间隔的确定等定量评估。地震地表破裂的同震位移分布十分复杂,影响因素也多种多样。汶川8.0级地震是一个以逆冲型为主的破裂事件,同震位移多表现为垂直位错,同时也存在右旋走滑位移,这与震源机制解的结果以及破裂面上擦痕所显示的运动方式基本一致。此次地震的最大同震水平位移量为4.5m,附近还有高达5m的垂直位移量。破裂的几何学和运动学分析表明,最大水平位移量可能是逆冲量沿不同方向破裂带分解以及断裂倾角变化的结果     

关于1999年岫岩偏岭5.6级地震前震群序列性质的研究

利用经验类比的方法,对１９９９年１１月２９日岫岩偏岭５．６级地震前群序列及以往在辽宁地区发生的典型具有预报意义的１９８８年２月２５日彰武４．８级地震前岫岩偏岭兆震群和１９７５年２月４日海城７．３级地震前序列进行了详细研究。结果显示,１９９９年１１月２９日岫岩偏岭５．６级地震前震群序列与１９７５年２月４日海城７．３级地震前震序列的统计特征及性质相同,因此,认为该序列属于前震序列。同时, 将序列的表象     

对地震序列时间分布广义分维的初步探讨

以1990年4月26日共和7.0级地震为例,讨论了地震序列时间分布特征,发现用“标度变换法”求时间容量维时,很难找到严格意义上的无标度区,因而用“广义无标度区”的概念计算出一组“广义分维”。讨论了震级下限对“广义无标度区”及“广义分维”值的影响、实际地震分布与Poisson分布、随机Cantor集合的偏离等问题。对时间序列的“广义分维值”进行扫描发现,在强余震前个别标度区有降维现象。     

地震序列的特征震级研究

在研究各类地震序列震级一频度客观分布的基础上,我们对45个地震序列的特征震级M0的普遍特征及差别作了进一步研究。结果,为地震预报探讨了一种可能的方法一用特怔震级M0≥2．0（或平均震级M≥2．1）作为地震预报的一个前兆性指标。同时还发现,当序列中主要事件超过7级以后,M0和M均限定在很小的震级域内变化。     

兰德斯地震断层面及其附近余震产生的位移场研究

根据兰德斯(Landers)地震断层面及其附近余震目录计算这些余震产生的位移场, 并与根据兰德斯地震破裂面滑动分布计算的主震产生的位移场进行对比. 结果表明, 断层面及其附近余震产生位移场的方向与主震大体一致, 余震破裂总体来看是继承性的. 余震产生的位移场达厘米量级, 足可以被GPS观测所捕获. 在利用地震震后随时间变化位移场研究地球粘性结构、 地震震后滑动分布等地球物理问题时, 扣除余震产生的位移场可以最大限度地减小反演结果的不确定性, 得到符合实际的结果.      

用地震标定律研究丽江7.0级地震的破裂过程

本根据Ｈｅａｓｋｅｌｌ二维矩形地震破裂模式，导出了以ω立方的波谱衰减，在分析地震破裂过程特征、考虑三个主要的相似性假定基础上，即假定地震满足断层面几何相似、应力环境相似和动力学相似条件，研究了大小地震相似性问题的标度分析，建立了地震破裂和源参数之间的标定律关系。用云南地区２０多年中数百个地震的地震矩Ｍ０、面波震级Ｍｓ和近震震级ＭＬ系统以及有关的地震参数，建立了适用于云南地区的地震标定律关系。由此     

基于高频GNSS的2014年2月12日于田Ms7．3地震的同震位移研究

于田Ms7．3地震后,第一时间收集到震中350km范围内4个基准站1Hz高频数据,并用TRACK模块进行解算,研究结果发现,①距离震中54km处的于田基准站同震变化最明显,尤其是东西分量,变化幅度达52．5±11mm,超过解算精度3倍中误差;②于田基准站东西分量出现变化量值最大的时间在震后1min内;③北南分量变化不大。     

以震源精确定位结果分析张北地震序列的破裂特征

利用远场和近场数字地震观测记录 ,重新测定了张北地震序列ML≥ 3级地震的震源位置 ,结合修订后的震源机制、宏观烈度分布资料 ,给出了张北地震序列的破裂特征。地震序列由走向NWW、倾向NNE、倾角 4 4°、长 11.5km的左旋走向滑动的主破裂面 ,2条NNE走向、高倾角、右旋走滑的次要破裂面组合而成。NWW和NNE走向的破裂面共轭展布 ,2条NNE向的破裂面呈右阶斜列 ,3条破裂面先后依次出现。破裂面埋深 1.4～ 7.6km ,在地壳的浅部。研究表明 ,在没有发现活动断裂的“构造稳定区” ,利用精确可靠的强震序列震源位置、震源机制和宏观烈度分布资料 ,从三维空间分析研究强震序列的震源断层 ,是一条可行的途径     

青海玉树单台地震序列的尾波Q值研究

利用玉树单台记录到的2006年7月19日玉树Ms5．4级地震序列的数字地震波形资料，计算了不同频率下该序列尾波Q值的变化特征，为今后将数字地震资料应用到地震预报工作中提供了参考依据。     

伽师强震群序列的破列特征

分析了伽师强震群序列中13次5级以上地震的震源机制解资料，其中有8个走滑型地震、5个倾滑型地震。走滑型地震的北北西向节面与Ms≥5．0级地震震中分布的斜列线一致，伽师强震群序列可能是北北西向右旋走滑断层及与其斜交的张性正断层共同作用的结果。     

地震时间序列的突变分析

采用Ｍａｎｎ－Ｋｅｎｄａｌｌ非参数方法检验了陕西及邻省的历史及现今地震序列，发现存在若干突变点，在其前后地震频次和强度发生非连续时间变化。这个研究有助于地震演变规律认识。     

丽江7.0级地震前地震活动特征

本论述了丽江７．０级地震前地震活动条带、能量释放加速、复发周期时间扫描、剪切应力值异常等地震活动性的中长期背景异常和ｂ值、缺震、振幅比、剪切应力场地动态分布、地震窗等短期异常。     

安庆4.8级地震序列的地震波谱变化研究

采用安徽区域数字地震台网记录的安庆4.8级地震序列波形资料,开展地震波谱研究,求取了零频位移谱值、应力降和地震矩等震源参数。分析了纵、横波零频谱值比和应力降随时间的变化趋势,并讨论了震源参数之间的关系。结果表明,安庆4.8级主震后,纵、横波零频位移谱值比和应力降呈现一定的变化规律,可为主震—余震序列的最大余震的预测提供一定的参考依据,同时发现震源参数与震级有一定相关。     

用相对定位法精细测定张北地震序列的时空参数

使用笔者改进了的相对地震定位方法对１９９８年１月１０日至５月３１日的张北地震序列中ＭＬ３．０级以上地震进行了重新测定,由于相对定位法能在一定程度上抵消地壳速度结构的横向不均匀性地震定位的影响,从而取得了较常规定位方法更精细的结果。     

1812年尼勒克地震断层及最大位移

通过野外考察和地貌变形测量等手段,研究了尼勒克1812年8级地震的地震断层的平面分组特点、活动性质、分段特征,讨论了地震滑塌构造、地震断层与重力滑坡的区别,分析了线性滑坡后壁与地震断层的潜在关系。在正确区分地震断层和滑坡后壁的基础上,确定了地震断层的最大位移。该形变带从吉仁台延伸到乔尔马以东,东西总长124 km,南北最宽处约28 km,地震断层断续展布97 km,最大垂直错距为15 m,水平位移为4 m。