Joint inversion of GNSS and teleseismic data for the rupture process of the 2017 <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript>6.5 Jiuzhaigou,China, earthquake

The spatio-temporal slip distribution of the earthquake that occurred on 8 August 2017 in Jiuzhaigou, China, was estimated from the teleseismic body wave and near-field Global Navigation Satellite System (GNSS) data (coseismic displacements and high-rate GPS data) based on a finite fault model. Compared with the inversion results from the teleseismic body waves, the near-field GNSS data can better restrain the rupture area, the maximum slip, the source time function, and the surface rupture. The results show that the maximum slip of the earthquake approaches 1.4 m, the scalar seismic moment is ~ 8.0 × 10¹⁸ N·m (M_w?≈?6.5), and the centroid depth is ~ 15 km. The slip is mainly driven by the left-lateral strike-slip and it is initially inferred that the seismogenic fault occurs in the south branch of the Tazang fault or an undetectable fault, a NW-trending left-lateral strike-slip fault, and belongs to one of the tail structures at the easternmost end of the eastern Kunlun fault zone. The earthquake rupture is mainly concentrated at depths of 5–15 km, which results in the complete rupture of the seismic gap left by the previous four earthquakes with magnitudes >?6.0 in 1973 and 1976. Therefore, the possibility of a strong aftershock on the Huya fault is low. The source duration is ~ 30 s and there are two major ruptures. The main rupture occurs in the first 10 s, 4 s after the earthquake; the second rupture peak arrives in ~ 17 s. In addition, the Coulomb stress study shows that the epicenter of the earthquake is located in the area where the static Coulomb stress change increased because of the 12 May 2017 M_w7.9 Wenchuan, China, earthquake. Therefore, the Wenchuan earthquake promoted the occurrence of the 8 August 2017 Jiuzhaigou earthquake.     

2018年阿拉斯加湾MW7.9地震震源复杂性

2018年1月23日,在美国阿拉斯加湾海域发生了一次M_W7.9地震.震源机制解表明这次地震以走滑为主,可能发生在近东西向或南北向的陡倾角断层上,早期余震并非线型展布.我们利用视震源时间函数分析确定了此次地震的总体破裂方向,并结合余震的空间展布特征构建了相互交叉的双断层模型,进而通过联合反演远场P波和SH波数据获得了此次地震的时空破裂过程.视震源时间函数分析表明总体破裂方向既非东西也非南北,而且反演结果表明,两个断层上都发生了错动,总体破裂时间~50 s,释放标量地震矩~8.11×10²⁰ Nm.震源时间函数表现出多事件特征,且两个断层破裂的时间过程也不相同.破裂首先在南北向断层的南端开始,很快触发了东西向断层,最后终止于南北向断层的北端.每个断层都具有相当的时空复杂性,位错分布很不均匀.东西向断层具有三个凹凸体,一个位于震源附近,其他两个位于断层两端.南北向断层有两个凹凸体,均位于断层北段,最大滑动量~5.0 m就出现在这里.发生最大位错的南北向断层延伸至阿拉斯加海沟,增加了触发阿拉斯加海沟其他断层发生破裂的可能性.     

A Rupture Model for the 1999 Chi-Chi Earthquake from Inversion of Teleseismic Data Using the Hybrid Homomorphic Deconvolution Method

This study investigates the kinematics of the rupture process of the M _L 7.3 Chi–Chi, Taiwan, earthquake on September 21, 1999. By applying the proposed hybrid homomorphic deconvolution method to deconvolve teleseismic broadband P-wave displacement recordings of the earthquake, this study derives the apparent source time functions (ASTFs) at ten stations located around the epicenter. To further characterize the fault, the kinematic history of the rupture was inverted from ASTFs using a genetic algorithm, coupled with nonlinear iterative technique. The calculated ASFTs reveal that the total rupture event lasted for approximately 27 s. Static slip distribution images indicate that most slip occurred at shallower portions of the fault plane, especially 20–55 km north of the epicenter. The maximum slip reached 20 m at 45 km north of the epicenter, and the average slip throughout the observed rupture area was approximately 2 m. Large asperities on the fault appeared at 25–35 km and 40–50 km north of the hypocenter, and coincided with relatively high rupture velocity. This suggests that the earthquake’s energy may have been released quickly. The rupture velocity decreased upon encountering an asperity, and increased again after passing the asperity. This implies that the rupture required more time to overcome the resistances of the asperities. The maximum rupture velocity was 3.8 km/s, while the average rupture velocity was approximately 2.2 km/s. The rise time distribution suggests that larger slip amplitudes generally correspond to shorter rise times on the subfaults.     

2012年江苏高邮、宝应交界MS4.9地震发震断层参数测定

基于一维单侧有限移动震源模式,根据地震波传播过程中的多普勒效应,分别利用P波和S波拐角频率的方位变化,反演2012年7月20日江苏高邮、宝应交界MS4.9地震的发震断层面参数。P波和S波拐角频率的反演结果一致显示:本次地震的断层面破裂方向为232°左右,破裂面呈NE-SW向;地震马赫数v/c为0.2左右,平均破裂速度小于S波速度,破裂长度较短,为0.2~0.3km左右。破裂面方位与震源机制解、宏观烈度调查和余震精定位的研究结果具有一致性,结合震区周边的地质构造背景,分析认为滁河断裂很可能是高邮、宝应交界MS4.9地震的发震构造。     

山东及附近区域地震断层错动性质与地壳应力场特征

利用P、SH、SV波的初动及振幅比获得2001年4月至2012年8月山东及附近区域132次地震震源机制解,对该区域地震断层的错动性质及地壳应力场特征进行分析.结果表明,山东及附近区域地震断层错动的基本方向为北东向和北西向,错动方式以走向滑动为主,部分为斜向滑动.分区研究表明：聊考断裂带附近区域所受挤压作用相对较强,逆断型地震破裂较多;胶东半岛及北侧海域所受拉张作用略占优势,逆断型地震破裂较少;沂沭断裂带南部附近区域逆断型与正断型的地震破裂所占比例差别不大.     

Numerical simulation of strong ground motion for the M_s8.0 Wenchuan earthquake of 12 May 2008

The Wenchuan earthquake of 12 May 2008 is the most destructive earthquake in China in the past 30 years in terms of property damage and human losses. In order to understand the earthquake process and the geo-morphological factors affecting the seismic hazard, we simulated the strong ground mo-tion caused by the earthquake, incorporating three-dimensional (3D) earth structure, finite-fault rupture, and realistic surface topography. The simulated ground motions reveal that the fault rupture and basin structure control the overall pattern of the peak ground shaking. Large peak ground velocity (PGV) is distributed in two narrow areas: one with the largest PGV values is above the hanging wall of the fault and attributed to the locations of fault asperities and rupture directivity; the other is along the north-western margin of the Sichuan Basin and caused by both the directivity of fault rupture and the ampli-fication in the thick sediment basin. Rough topography above the rupture fault causes wave scattering, resulting in significantly larger peak ground motion on the apex of topographic relief than in the valley. Topography and scattering also reduce the wave energy in the forward direction of fault rupture but increase the PGV in other parts of the basin. These results suggest the need for a localized hazard as-sessment in places of rough topography that takes the topographic effects into account. Finally, had the earthquake started at the northeast end of the fault zone and ruptured to the southwest, Chengdu would have suffered a much stronger shaking than it experienced on 12 May, 2008.     

2014年新疆于田MS7.3地震序列重定位及其发震构造初步研究

2014年2月12日在新疆于田县发生了M_S7.3地震,主震前一天在震区发生了M_S5.4前震,震后余震活动频繁,由于震区台站十分稀疏和不均匀、地壳速度结构复杂,台网常规定位结果精度有限,很难从中获得序列的空间分布特征和活动趋势的正确认识.本文首先利用位于震区附近的于田地震台5年记录的远震波形数据,采用接收函数方法研究了震区附近的地壳结构,建立了震源区的地壳速度模型.在此基础上,联合震相到时和方位角对2014年于田M_S7.3地震序列(从2014年02月11日-2014年04月30日,共计577次地震)进行了重新绝对定位.结果显示,(1) 重定位后的前震和主震震中位置明显向地表破裂带及其附近的阿尔金分支断裂(南肖尔库勒断裂和阿什库勒-肖尔库勒断裂)靠近,两者相距5.4 km,主震位置为36.076°N、82.576°E,震源深度为22 km, 前震位置为36.055°N、82.522°E,震源深度为19 km;(2) 本文重定位结果显示,余震序列沿NEE-SWW展布,优势分布长度约73 km、宽度约16 km,平均震源深度为14.8 km,其中77%的余震分布在地表破裂带的西南端,这部分余震中少数沿阿什库勒-肖尔库勒断裂分布,绝大多数沿北东东向的南肖尔库勒断裂分布,位于地表破裂带东北端的余震沿阿什库勒-肖尔库勒断裂分布,但发生在地表破裂带的余震极少;重定位后,位于地表破裂带西南侧的震中分布由台网目录的近南北向变为北东向,与地表破裂带、南肖尔库勒断裂和阿什库勒-肖尔库勒断裂走向一致;(3) 沿重定位剖面的地震分布,可推断位于地表破裂带西南段的南肖尔库勒断裂与位于北东段的阿什库勒-肖尔库勒断裂倾向反向,南肖尔库勒断裂的倾向为SE,阿什库勒-肖尔库勒断裂的倾向为NW,这与本次地震野外考察得到的断裂性质一致.综合重定位结果、地表破裂带分布、震源机制解、南肖尔库勒断裂和阿什库勒-肖尔库勒断裂的性质认为,2014年于田M_S7.3地震的发震构造为阿尔金断裂西南尾段的两条分支断裂——南肖尔库勒断裂和阿什库勒-肖尔库勒断裂.     

1996年3月19日新疆阿图什6.9级地震震源破裂特征的研究

通过对1996年3月19日新疆阿图什6．9级地震余震分布特征的研究，分析了这次地震震源破裂过程．并结合柯坪断裂带的构造运动、区域应力场的分布特征以及1972年以来该带的另外3次6级地震的余震分布方向，探讨了柯坪断裂带附近地区不同构造部位震源破裂扩展方向与强震活动的迁移方向．结果表明，本次地震震源破裂为明显的单侧破裂．柯坪断裂带的阿图什震区和柯坪震区，余震分布具有一定规律性，震源破裂基本都为单侧破裂；震源断错以逆断层为主．区内主要受NW向压应力。不同地段强震震源破裂扩展具有明显的区域特征，强余震分布方向是应力集中的体现，它标志着同一构造断裂带附近近期强震活动的迁移方向．在柯坪断裂带上这种规律更为明显。     

Seismic Imaging of a Bimaterial Interface Along the Hayward Fault,CA, with Fault Zone Head Waves and Direct P Arrivals

We observe fault zone head waves (FZHW) that are generated by and propagate along a roughly 80 km section of the Hayward fault in the San Francisco Bay area. Moveout values between the arrival times of FZHW and direct P waves are used to obtain average P-wave velocity contrasts across different sections of the fault. The results are based on waveforms generated by more than 5,800 earthquakes and recorded at up to 12 stations of the Berkeley digital seismic network (BDSN) and the Northern California seismic network (NCSN). Robust identification of FZHW requires the combination of multiple techniques due to the diverse instrumentation of the BDSN and NCSN. For single-component short-period instruments, FZHW are identified by examining sets of waveforms from both sides of the fault, and finding on one (the slow) side emergent reversed-polarity arrivals before the direct P waves. For three-component broadband and strong-motion instruments, the FZHW are identified with polarization analysis that detects early arrivals from the fault direction before the regular body waves which have polarizations along the source-receiver backazimuth. The results indicate average velocity contrasts of 3–8 % along the Hayward fault, with the southwest side having faster P wave velocities in agreement with tomographic images. A systematic moveout between the FZHW and direct P waves for about a 80 km long fault section suggests a single continuous interface in the seismogenic zone over that distance. We observe some complexities near the junction with the Calaveras fault in the SE-most portion and near the city of Oakland. Regions giving rise to variable FZHW arrival times can be correlated to first order with the presence of lithological complexity such as slivers of high-velocity metamorphic serpentinized rocks and relatively distributed seismicity. The seismic velocity contrast and geological complexity have important implications for earthquake and rupture dynamics of the Hayward fault, including a statistically preferred propagation direction of earthquake ruptures to the SE.     

Numerical simulation of strong ground motion for the <Emphasis Type="Italic">M</Emphasis><Subscript>s</Subscript>8.0 Wenchuan earthquake of 12 May 2008

The Wenchuan earthquake of 12 May 2008 is the most destructive earthquake in China in the past 30 years in terms of property damage and human losses. In order to understand the earthquake process and the geo-morphological factors affecting the seismic hazard, we simulated the strong ground motion caused by the earthquake, incorporating three-dimensional (3D) earth structure, finite-fault rupture, and realistic surface topography. The simulated ground motions reveal that the fault rupture and basin structure control the overall pattern of the peak ground shaking. Large peak ground velocity (PGV) is distributed in two narrow areas: one with the largest PGV values is above the hanging wall of the fault and attributed to the locations of fault asperities and rupture directivity; the other is along the northwestern margin of the Sichuan Basin and caused by both the directivity of fault rupture and the amplification in the thick sediment basin. Rough topography above the rupture fault causes wave scattering, resulting in significantly larger peak ground motion on the apex of topographic relief than in the valley. Topography and scattering also reduce the wave energy in the forward direction of fault rupture but increase the PGV in other parts of the basin. These results suggest the need for a localized hazard assessment in places of rough topography that takes the topographic effects into account. Finally, had the earthquake started at the northeast end of the fault zone and ruptured to the southwest, Chengdu would have suffered a much stronger shaking than it experienced on 12 May, 2008. Supported by the U.S. National Science Foundation (Grant Nos. EAR 0738779 and OCE 0727919), the National Basic Research Program of China (Grant No. 2004CB418404), and partially by the National Nature Science Foundation of China (Grant No. 40521002)     

Spatial and temporal rupture process of the January 26, 2001, Gujarat, India, M S=7.8 earthquake

The source parameters, such as moment tensor, focal mechanism, source time function (STF) and temporal-spatial rupture process, were obtained for the January 26, 2001, India, M _S=7.8 earthquake by inverting waveform data of 27 GDSN stations with epicentral distances less than 90°. Firstly, combining the moment tensor inversion, the spatial distribution of intensity, disaster and aftershocks and the orientation of the fault where the earthquake lies, the strike, dip and rake of the seismogenic fault were determined to be 92°, 58° and 62°, respectively. That is, this earthquake was a mainly thrust faulting with the strike of near west-east and the dipping direction to south. The seismic moment released was 3.5×10²⁰ Nm, accordingly, the moment magnitude M _W was calculated to be 7.6. And then, 27 P-STFs, 22 S-STFs and the averaged STFs of them were determined respectively using the technique of spectra division in frequency domain and the synthetic seismogram as Green’s functions. The analysis of the STFs suggested that the earthquake was a continuous event with the duration time of 19 s, starting rapidly and ending slowly. Finally, the temporal-spatial distribution of the slip on the fault plane was imaged from the obtained P-STFs and S-STFs using an time domain inversion technique. The maximum slip amplitude on the fault plane was about 7 m. The maximum stress drop was 30 MPa, and the average one over the whole rupture area was 7 MPa. The rupture area was about 85 km long in the strike direction and about 60 km wide in the down-dip direction, which, equally, was 51 km deep in the depth direction. The rupture propagated 50 km eastwards and 35 km westwards. The main portion of the rupture area, which has the slip amplitude greater than 0.5 m, was of the shape of an ellipse, its major axis oriented in the slip direction of the fault, which indicated that the rupture propagation direction was in accordance with the fault slip direction. This phenomenon is popular for strike-slip faulting, but rather rare for thrust faulting. The eastern portion of the rupture area above the initiation point was larger than the western portion below the initiation point, which was indicative of the asymmetrical rupture. In other words, the rupturing was kind of unilateral from west to east and from down to up. From the snapshots of the slip-rate variation with time and space, the slip rate reached the largest at the 4th second, that was 0.2 m/s, and the rupture in this period occurred only around the initiation point. At the 6th second, the rupture around the initiation point nearly stopped, and started moving outwards. The velocity of the westward rupture was smaller than that of the eastward rupture. Such rupture behavior like a circle mostly stopped near the 15th second. After the 16th second, only some patches of rupture distributed in the outer region. From the snapshots of the slip variation with time and space, the rupture started at the initiation point and propagated outwards. The main rupture on the area with the slip amplitude greater than 5 m extended unilaterally from west to east and from down to up between the 6th and the 10th seconds, and the western segment extended a bit westwards and downwards between the 11th and the 13th seconds. The whole process lasted about 19 s. The rupture velocity over the whole rupture process was estimated to be 3.3 km/s. Foundation item: 973 Project (G1998040705) from Ministry of Science and Technology, P. R. China, and the National Science Foundation of China under grant No.49904004. Contribution No. 02FE2026, Institute of Geophysics, China Seismological Bureau.     

23 October 2011 Van, Eastern Anatolia, earthquake (M W 7.1) and seismotectonics of Lake Van area

The 23 October 2011 Van earthquake took place in the NE part of Lake Van area, surprisingly on a fault (the Van fault) that is not present in the current active fault map of Turkey. However, occurrence of such a large magnitude earthquake in the area is not surprising regarding the historical seismicity of the region. The comparison of the damage patterns suggests that the earthquake is much likely a recurrence of the 1715 Van earthquake. The finite fault modelling of the earthquake using teleseismic broadband body waveforms has shown that the earthquake rupture was unilateral toward SW, was mostly reverse faulting, confined to below the depth of 5 km, did not propagate offshore, and was dominated by a failure of a single asperity with a peak slip of about 5.5 m. The total seismic moment calculated for the model is 4.6?×?10¹⁹ Nm (M _W ?≈?7.1). The finite fault model coincides with the field observations indicating blind faulting and the vertical displacements over the free surface estimated from it correlate well with the maximum reported uplift along the coast of Lake Van above the hanging wall. The possible offshore continuations of the Van fault and some other faults lying its south are also discussed by assessing a previous offshore seismic reflection study and the earthquake epicentres and focal mechanisms.     

Spatio-temporal properties and evolution of the 2013 Aigion earthquake swarm (Corinth Gulf,Greece)

The 2013 Aigion earthquake swarm that took place in the west part of Corinth Gulf is investigated for revealing faulting and seismicity properties of the activated area. The activity started on May 21 and was appreciably intense in the next 3 months. The recordings of the Hellenic Unified Seismological Network (HUSN), which is adequately dense around the affected area, were used to accurately locate 1501 events. The double difference (hypoDD) technique was employed for the manually picked P and S phases along with differential times derived from waveform cross-correlation for improving location accuracy. The activated area with dimensions 6?×?2 km is located approximately 5 km SE of Aigion. Focal mechanisms of 77 events with M?≥?2.0 were determined from P wave first motions and used for the geometry identification of the ruptured segments. Spatio-temporal distribution of earthquakes revealed an eastward and westward hypocentral migration from the starting point suggesting the division of the seismic swarm into four major clusters. The hypocentral migration was corroborated by the Coulomb stress change calculation, indicating that four fault segments involved in the rupture process successively failed by stress change encouragement. Examination of fluid flow brought out that it cannot be unambiguously considered as the driving mechanism for the successive failures.     

Seismological asperities from the point of view of dynamic rupture modeling: the 2007 Mw6.6 Chuetsu-Oki,Japan, earthquake

We study the ground motion simulations based on three finite-source models for the 2007 Mw6.6 Niigata Chuetsu-oki, Japan, earthquake in order to discuss the performance of the input ground motion estimations for the near-field seismic hazard analysis. The three models include a kinematic source inverted from the regional accelerations, a dynamic source on a planar fault with three asperities inferred from the very-near-field ground motion particle motions, and another dynamic source model with conjugate fault segments. The ground motions are calculated for an available 3D geological model using a finite-difference method. For the comparison, we apply a goodness-of-fit score to the ground motion parameters at different stations, including the nearest one that is almost directly above the ruptured fault segments. The dynamic rupture models show good performance. We find that seismologically inferred earthquake asperities on a single fault plane can be expressed with two conjugate segments. The rupture transfer from one segment to another can generate a significant radiation; this could be interpreted as an asperity projected onto a single fault plane. This example illustrates the importance of the fault geometry that has to be taken into account when estimating the very-near-field ground motion.     

2022年1月8日青海门源MS6.9地震强地面运动模拟及烈度分布估计

2022年1月8日青海省海北藏族自治州门源回族自治县发生M_S6.9地震。门源地震序列的重定位结果认为门源地区还存在一定的应力积累,未来该地区具有发生强震的可能。本文结合震源区地形数据、三维速度结构,根据门源地震震源破裂过程的初步结果,采用曲线网格有限差分方法模拟了门源地震的波场传播过程,得到烈度分布。结果表明:沿平行断层走向方向的地震动衰减明显小于垂直断层走向方向;门源地震的最大烈度为Ⅷ度,位于震源破裂起始点附近区域,理论烈度与野外调查的地震烈度分布基本一致;受强地面运动方向性效应和起伏地表的影响,地震灾害主要沿发震断层的WNW方向和ESE方向集中分布。      

Coseismic deformation of the 2021 MW7.4 Maduo earthquake from joint inversion of InSAR,GPS, and teleseismic data

The M_W7.4 Maduo earthquake occurred on 22 May 2021 at 02:04 CST with a large-expansion surface rupture. This earthquake was located in the Bayan Har block at the eastern Tibetan Plateau, where eight earthquakes of M_S >7.0 have occurred in the past 25 years. Here, we combined interferometric synthetic aperture radar, GPS, and teleseismic data to study the coseismic slip distribution, fault geometry, and dynamic source rupture process of the Maduo earthquake. We found that the overall coseismic deformation field of the Maduo earthquake is distributed in the NWW-SEE direction along 285°. There was slight bending at the western end and two branches at the eastern end. The maximum slip is located near the eastern bending area on the northern branch of the fault system. The rupture nucleated on the Jiangcuo fault and propagated approximately 160 km along-strike in both the NWW and SEE directions. The characteristic source rupture process of the Maduo earthquake is similar to that of the 2010 M_W6.8 Yushu earthquake, indicating that similar earthquakes with large-expansion surface ruptures and small shallow slip deficits can occur on both the internal fault and boundary fault of the Bayan Har block.     

台湾双冬断层近场脉冲型地震动的数值模拟

根据我国台湾地区西部的地质地貌特征和1999年集集M_W7.6地震的震源参数,建立了三维速度结构模型和两类震源模型。基于地壳中断层的位错积累量和岩石破裂后应力应变的传播特性,采用三维有限差分法对双冬断层活动可能产生的近场脉冲型地震动进行了模拟研究。结果表明:走滑断层垂直于断层走向的水平分量和逆断层垂直分量的峰值速度较大;由方向性效应所产生的双向速度脉冲主要集中在垂直于断层滑动分量方向,而由滑冲效应所产生的单向速度脉冲则主要集中在平行于断层滑动分量的方向;受方向性效应和上盘效应的共同制约,近场脉冲型地震动呈不对称带状分布,速度脉冲多分布在距离走滑断层迹线15 km和逆断层迹线10 km的范围内;速度反应谱在断层面的覆盖范围内沿破裂方向逐渐增大,且速度脉冲可能会对大型建筑物产生严重的剪切破坏。受凹凸体特性的影响,地震波场显示南投、台中和苗栗处于强地震动危险区。      

断层间相互作用与地震触发机制的研究进展

计算地震引起的静、动应力变化量空间分布图象是国内外研究断层间相互作用与地震触发机制的两个主要方法。依据半弹性空间地震位错理论获得的静应力变化量，可以长期存在于邻近断层面上，直至下一次地震发生。因此，静应力变化量空间分布图象既被用来解释一次地震后余震活动在邻近断层上的分布规律，又被用来研究一个地区几十年至几百年地震活动过程中断层问相互作用特点和强震迁移规律。但静应力变化量随距离缩减快，空间分布与地震破裂扩展方向无关。动应力随距离衰减速度慢，量值大；在地震破裂扩展方向上，动应力变化量可以比相反方向高出一个数量级。由于动应力是伴随地震波传播而出现的，因此，动应力变化量是暂态的，作用于邻近断层面上时间有限。在分析国内外研究现状的基础上，提出我国目前在该研究领域所面临的一些问题，并说明了解决这些问题的主要技术途径。     

Tempo-spatial rupture process of the 1997 Mani, Xizang (Tibet), China earthquake of M S=7.9

An earthquake of M _S=7.4 occurred in Mani, Xizang (Tibet), China on November 8, 1997. The moment tensor of this earthquake was inverted using the long period body waveform data from China Digital Seismograph Network (CDSN). The apparent source time functions (ASTFs) were retrieved from P and S waves, respectively, using the deconvolution technique in frequency domain, and the tempo-spatial rupture process on the fault plane was imaged by inverting the azimuth dependent ASTFs from different stations. The result of the moment tensor inversion indicates that the P and T axes of earthquake-generating stress field were nearly horizontal, with the P axis in the NNE direction (29°), the T axis in the SEE direction (122°) and that the NEE-SWW striking nodal plane and NNW-SSE striking nodal plane are mainly left-lateral and right-lateral strike-slip, respectively; that this earthquake had a scalar seismic moment of 3.4×10²⁰ N·m, and a moment magnitude of M _W=7.6. Taking the aftershock distribution into account, we proposed that the earthquake rupture occurred in the fault plane with the strike of 250°, the dip of 88° and the rake of 19°. On the basis of the result of the moment tensor inversion, the theoretical seismograms were synthesized, and then the ASTFs were retrieved by deconvoving the synthetic seismograms from the observed seismograms. The ASTFs retrieved from the P and S waves of different stations identically suggested that this earthquake was of a simple time history, whose ASTF can be approximated with a sine function with the half period of about 10 s. Inverting the azimuth dependent ASTFs from P and S waveforms led to the image showing the tempo-spatial distribution of the rupture on the fault plane. From the "remembering" snap-shots, the rupture initiated at the western end of the fault, and then propagated eastward and downward, indicating an overall unilateral rupture. However, the slip distribution is non-uniform, being made up of three sub-areas, one in the western end, about 10 km deep ("western area"); another about 55 km away from the western end and about 35 km deep ("eastern area"); the third about 30 km away from the western end and around 40 km deep ("central area"). The total rupture area was around 70 km long and 60 km wide. From the "forgetting" snap-shots, the rupturing appeared quite complex, with the slip occurring in different position at different time, and the earthquake being of the characteristics of "healing pulse". Another point we have to stress is that the locations in which the rupture initiated and terminated were not where the main rupture took place. Eventually, the static slip distribution was calculated, and the largest slip values of the three sub-areas were 956 cm, 743 cm and 1 060 cm, for the western, eastern and central areas, respectively. From the slip distribution, the rupture mainly distributed in the fault about 70 km eastern to the epicenter; from the aftershock distribution, however, the aftershocks were very sparse in the west to the epicenter while densely clustered in the east to the epicenter. It indicated that the Mani M _S=7.9 earthquake was resulted from the nearly eastward extension of the NEE-SWW to nearly E-W striking fault in the northwestern Tibetan plateau. Contribution No. 99FE2016, Institute of Geophysics, China Seismological Bureau. This work is supported by SSTCC Climb Project 95-S-05 and NSFDYS 49725410.     

2015年尼泊尔Gorkha地震强地面运动记录分析

2015年4月25日在尼泊尔Gorkha地区发生M_W7.8地震,距离发震断层约11 km的KATNP台站完整记录了主震的加速度时程.本文根据KATNP台站记录的加速度数据分析了Gorkha地震的地震动特征.结果表明Gorkha地震在KATNP台站处产生的水平向峰值加速度为0.17 g,竖直向峰值加速度为0.19 g,该数值小于科学家们对如此大规模地震产生的地震动的预期,初步推测这可能是由加德满都山谷产生的非线性响应造成的（Dixit et al.,2015）;地震在KATNP台站处产生了地表永久位移,其中竖向永久位移为131.9 cm,水平向永久位移的绝对值为159.2 cm,方向为南偏西19°（199°）,据此可简单推算出断层走向约为289°（109°）.地震产生了脉冲型地震动,影响因素有盆地效应、地震破裂的向前的方向性效应以及滑冲效应,其中盆地效应的周期约为5 s左右,方向性效应产生的速度脉冲的周期约为8 s左右.加速度反应谱显示在0.5 s和5.0 s左右各有一个峰值,前者是由地震破裂的脉冲式滑移产生的大量高频地震动造成的,后者是由于盆地效应和地震破裂的方向性效应造成的.基于阿里亚斯烈度计算的地震动持时约在36~46 s之间,小于与其规模相当的地震产生的地震动持时,并且不同方向上的地震动持时可能与地震破裂方向有关.阿里亚斯烈度随时间的变化比较简单,也反映了Gorkha地震是一次连续的、能量释放相对简单的地震事件.