基于恢复地震数据获取震级、震源机制及破裂过程的评价——以2013年四川芦山MW6.6地震为例

区域地震波形对于震源研究非常重要,但限幅问题限制了区域地震台网数据的运用,并影响到震源参数测定的准确度.本文利用恢复后的芦山地震区域地震波形,研究了芦山地震的震级、点源机制解以及破裂过程.基于震中距99~300 km恢复前与恢复后地震数据获取的面波震级分别为7.01与7.06级.分别利用7个震中距150~250 km宽频带台站的恢复前和恢复后的数据反演点源机制解,与参考机制解相比,滑动角偏差自13°减小到了4°.基于7个震中距81~134 km的区域地震波形联合远场数据获得的震源破裂过程结果,其主要参数（如滑动分布、破裂速度等）与强地面运动波形联合远场数据得到的结果具有很好的一致性.研究结果表明,本文所采用的数据恢复方法具有较高的可靠性,有效提高了震源参数测定的准确度.     

用接收函数方法研究汶川和芦山地震之间未破裂段的地壳结构

芦山与汶川地震之间存在约40 km的地震空区.震源区和地震空区的深部构造背景的研究对深入了解中强地震的深部孕育环境及地震空区的地震活动性具有重要科学意义.利用本小组布设的15个临时观测地震台以及21个芦山科考台站和21个四川省地震局固定台站记录的远震数据,用H-K叠加方法得到各个台站的地壳厚度和平均泊松比,并构建了接收函数共转换点(CCP)偏移叠加图像以及反演得到台站下方的S波速度模型.我们的结果揭示了震源区和地震空区地壳结构特征差异:(1)汶川震源区的地壳平均泊松比为~0.28;芦山震源区为~0.29;而地震空区处于泊松比变化剧烈的区域;(2)汶川地震与芦山地震的震源区以西下方的Moho面呈现深度上的突变(这与前人的研究成果基本一致),分别从~44 km突变到~59 km,~40 km突变到~50 km,而地震空区地壳平均厚度呈现渐变性变化;(3)地震空区Moho面下凹且具有低速的上地壳.综合一维S波速度结构和H-k以及CCP的初步结果,这可能显示汶川地震的发震断裂在深部方向上向西倾斜并形成切割整个地壳的大型断裂;芦山地震则可能是由于上、下地壳解耦引起的;而地震空区处于两种地震形成机制控制区域的过渡带中.     

2013年4月20日四川芦山MS7.0地震:一个高角度逆冲地震

利用中国地震台网和IRIS数据中心提供的近远震数字地震波形记录,首先读取P波初动方向,在考虑深度误差和速度模型引起的离源矢量误差基础上,利用网格搜索方法,计算了2013年4月20日四川芦山M_S7.0地震断层面解,其断层面走向/倾角/滑动角依次为212°/44°/92°.然后采用近远震波形联合反演方法(CAPjoint),反演了地震矩心深度和点源近似下双力偶解,表明地震发生在12 km深度,发震断层面参数为212°/47°/93°.通过分析波形反演中深度和震源区地震波速度模型对断层面倾角的影响,并结合短期余震机制解,认为芦山M_S7.0地震是一个高角度逆冲地震.     

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.     

核幔边界反射震相ScS对远震体波反演震源参数精度影响

研究表明,远震直达体波波形(P波、SH波)是有效反演中强地震(M5.5~7)震源参数的重要资料.但是当震中距较大时,核幔边界全反射波ScS会进入SH波反演窗口,其未被传统的基于体波震源参数反演算法所考虑,从而导致反演结果偏差.本文通过TEL3与fk方法合成理论地震图,使用Jackknifing统计方法定量测试了不同情况下ScS震相对远震体波反演的影响.结果表明,当反演数据震中距位于70°~90°时,ScS震相会造成震源质心深度1km左右、机制解最大8°的系统偏差;使用震中距40°~90°的SH波进行抽样反演,机制解最大系统偏差可达5°;SH波与P波联合反演可减少ScS震相引起的震源参数结果系统偏差.因此,ScS震相对基于射线理论的远震体波震源机制解反演所造成的误差是需要给予考虑的.     

Did the M S7.0 Lushan earthquake dynamically trigger earthquakes in the Datong volcanic region (Shanxi Province)?

Immediately following the M _S7.0 Lushan earthquake on April 20, 2013, using high-pass and low-pass filtering on the digital seismic stations in the Shanxi Province, located about 870–1,452 km from the earthquake epicenter, we detected some earthquakes at a time corresponding to the first arrival of surface waves in high-pass filtering waveform. The earthquakes were especially noticed at stations in Youyu (YUY), Shanzizao (SZZ), Shanghuangzhuang (SHZ), and Zhenchuan (ZCH), which are located in a volcanic region in the Shanxi Province,but they were not listed in the Shanxi seismic observation report. These earthquakes occurred 4–50 min after the passage of the maximum amplitude Rayleigh wave, and the periods of the surface waves were mainly between 15 and 20 s following. The Coulomb stresses caused by the Rayleigh waves that acted on the four stations was about 0.001 MPa, which is a little lower than the threshold value of dynamic triggering, therefore, we may conclude that the Datong volcanic region is more sensitive to the Coulomb stress change. To verify, if the similar phenomena are widespread, we used the same filtering to observe contrastively continuous waveform data before, and 5 h after, the M _S7.0 Lushan earthquake and M _S9.0 Tohoku earthquake in 2011. The results show that the similar phenomena occur before the earthquakes, but the seismicity rates after the earthquakes are remarkably increased. Since these weak earthquakes are quite small, it is hard to get clear phase arrival time from three or more stations to locate them. In addition, the travel time differences between P waves and S waves (S–P) are all less than 4 s, that means the events should occur in 34 km around the stations in the volcanic region. The stress of initial dynamic triggering of the M _S9.0 Tohoku earthquake was about 0.09 MPa, which is much higher than the threshold value of dynamic triggering stress. The earthquakes after the M _S9.0 Tohoku earthquake are related to dynamic triggering stress, but the events before the earthquake cannot be linked to seismic events, but may be related to the background seismicity or from other kinds of local sources, such as anthropogenic sources (i.e., explosions). Using two teleseismic filtering, the small background earthquakes in the Datong volcanic region occur frequently, thus we postulate that previous catalog does not apply bandpass filter to pick out the weak earthquakes, and some of the observed weak events were not triggered by changes in the dynamic stress field.     

f max and fault zone property of Lushan earthquake of 20 April 2013, Sichuan,China

In this study, we determined f _max from near-field accelerograms of the Lushan earthquake of April 20, 2013 through spectra analysis. The result shows that the values of f _max derived from five different seismography stations are very close though these stations roughly span about 100 km along the strike. This implies that the cause of f _max is mainly the seismic source process rather than the site effect. Moreover, according to the source–cause model of Papageorgiou and Aki (Bull Seism Soc Am 73:693–722, 1983), we infer that the cohesive zone width of the rupture of the Lushan earthquake is about 204 with an uncertainty of 13 m. We also find that there is a significant bulge between 30 and 45 Hz in the amplitude spectra of accelerograms of stations 51YAL and 51QLY, and we confirm that it is due to seismic waves’ reverberation of the sedimentary soil layer beneath these stations.     

2016年1月21日青海门源MS6.4余震序列重定位和主震震源机制解

2016年1月21日01时13分13.0秒（北京时间）,青海省海北州门源县发生M_S6.4地震.为了更好地认识这次地震的发震构造,本文利用青海省地震台网和甘肃省地震台网的省级固定地震台站及部分流动地震台站记录到的波形资料,通过重新拾取震相和联合HYPOINVERSE 2000与HypoDD定位方法,对2016年1月21日青海门源地震序列M_L≥1.8的189个地震事件进行了重新定位,并采用gCAP方法分别反演了主震的双力偶机制解和全矩张量解. 定位结果显示,主震位置为37.67°N、101.61°E,震源深度为11.98 km;余震序列展布方向为SE和NW两个方向、长度约16 km,震源深度优势分布为4~14 km,断层面倾向为SW方向. 利用gCAP方法得到的矩心深度在8~9 km之间. 结合野外地质调查结果,认为该次地震事件为一次逆冲型事件,其发震断层可能为北西向冷龙岭断裂与北西向民乐—大马营断裂之间的一条盲断层,推测由于印度板块与欧亚板块的碰撞挤压使得青藏高原北缘与阿拉善地块之间的东西向挤压而造成的断层应力失稳,从而形成门源地震.     

Seismic detections of the 15 February 2013 Chelyabinsk meteor from the dense ChinArray

Chin Array is a dense portable broadband seismic network to cover the entire continental China, and the Phase I is deployed along the north-south seismic belt in southwest China. In this study, we analyze seismic data recorded on the Chin Array following the February 15,2013 Chelyabinsk(Russia) meteor. This was the largest known object entering the Earth's atmosphere since the1908 Tunguska meteor. The seismic energy radiated from this event was recorded by seismic stations worldwide including the dense Chin Array that are more than 4000 km away. The weak signal from the meteor event was contaminated by a magnitude 5.8 Tonga earthquake occurred *20 min earlier. To test the feasibility of detecting the weak seismic signals from the meteor event, we compute vespagram and perform F-K analysis to the surface-wave data. We identify a seismic phase with back azimuth(BAZ) of 329.7° and slowness of 34.73 s/deg, corresponding to the surface wave from the Russian meteor event(BAZ *325.97°). The surface magnitude(MS) of the meteor event is 3.94 ± 0.18. We also perform similar analysis on the data from the broadband array F-net in Japan, and find the BAZ of the surface waves to be316.61°. With the different BAZs of Chin Array and F-net,we locate the Russian meteor event at 58.80°N, 58.72°E.The relatively large mislocation(*438 km as compared with 55.15°N, 61.41°E by others) may be a result of thebending propagation path of surface waves, which deviates from the great circle path. Our results suggest that the dense Chin Array and its subarrays could be used to detect weak signals at teleseismic distances.     

Source process of the 14 November 2001 western Kunlun Mountain <Emphasis Type="Italic">M</Emphasis><Subscript>S</Subscript>=8.1 earthquake

Based on digital teleseismic P-wave seismograms recorded by 28 long-period seismograph stations of the global seismic network, source process of the November 14, 2001 western Kunlun Mountain M _S=8.1 (M _W=7.8) earthquake is estimated by a new inversion method. The result shows that the earthquake is a very complex rupture event. The source rupture initiated at the hypocenter (35.95°N, 90.54°E, focal depth 10 km, by USGS NEIC), and propagated to the west at first. Then, in several minutes to a hundred minutes and over a large spatial range, several rupture growth points emerged in succession at the eastern end and in the central part of the finite fault. And then the source rupture propagated from these rupture growth points successively and, finally, stopped in the area within 50 km to the east of the centroid position (35.80°N, 92.91°E, focal depth 15 km, by Harvard CMT). The entire rupture lasted for 142 s, and the source process could be roughly separated into three stages: The first stage started at the 0 s and ended at the 52 s, lasting for 52 s and releasing approximately 24.4% of the total moment; The second stage started at the 55 s and ended at the 113 s, lasting for 58 s and releasing approximately 56.5% of the total moment; The third stage started at the 122 s and ended at the 142 s, lasting for 20 s and releasing approximately 19.1% of the total moment. The length of the ruptured fault plane is about 490 km. The maximum width of the ruptured fault plane is about 45 km. The rupture mainly occurred within 30 km in depth under the surface of the Earth. The average static slip in the underground rocky crust is about 1.2 m with the maximum static slip 3.6 m. The average static stress drop is about 5 MPa with the maximum static stress drop 18 MPa. The maximum static slip and the maximum stress drop occurred in an area within 50 km to the east of the centroid position.     

Source process of the 14 November 2001 western Kunlun Mountain M S=8.1 earthquake

Based on digital teleseismic P-wave seismograms recorded by 28 long-period seismograph stations of the global seismic network, source process of the November 14, 2001 western Kunlun Mountain M _S=8.1 (M _W=7.8) earthquake is estimated by a new inversion method. The result shows that the earthquake is a very complex rupture event. The source rupture initiated at the hypocenter (35.95°N, 90.54°E, focal depth 10 km, by USGS NEIC), and propagated to the west at first. Then, in several minutes to a hundred minutes and over a large spatial range, several rupture growth points emerged in succession at the eastern end and in the central part of the finite fault. And then the source rupture propagated from these rupture growth points successively and, finally, stopped in the area within 50 km to the east of the centroid position (35.80°N, 92.91°E, focal depth 15 km, by Harvard CMT). The entire rupture lasted for 142 s, and the source process could be roughly separated into three stages: The first stage started at the 0 s and ended at the 52 s, lasting for 52 s and releasing approximately 24.4% of the total moment; The second stage started at the 55 s and ended at the 113 s, lasting for 58 s and releasing approximately 56.5% of the total moment; The third stage started at the 122 s and ended at the 142 s, lasting for 20 s and releasing approximately 19.1% of the total moment. The length of the ruptured fault plane is about 490 km. The maximum width of the ruptured fault plane is about 45 km. The rupture mainly occurred within 30 km in depth under the surface of the Earth. The average static slip in the underground rocky crust is about 1.2 m with the maximum static slip 3.6 m. The average static stress drop is about 5 MPa with the maximum static stress drop 18 MPa. The maximum static slip and the maximum stress drop occurred in an area within 50 km to the east of the centroid position. Foundation item: Joint Seismological Science Foundation of China (103066) and Foundation of the Seismic Pattern and Digital Seismic Data Application Research Office of Institute of Earthquake Science of the China Earthquake Administration.     

2013年芦山地震序列震源机制与震源区构造变形特征分析

基于四川区域地震台网记录的波形资料,利用CAP波形反演方法,同时获取了2013年4月20日芦山M7.0级地震序列中88个M≥3.0级地震的震源机制解、震源矩心深度与矩震级,进而利用应变花（strain rosette）和面应变（areal strain）As值,分析了芦山地震序列震源机制和震源区构造运动与变形特征.获得的主要结果有：（1）芦山M7.0级主震破裂面参数为走向219°/倾角43°/滑动角101°,矩震级为M_W6.55,震源矩心深度15 km.芦山地震余震区沿龙门山断裂带走向长约37 km、垂直断裂带走向宽约16 km.主震两侧余震呈不对称分布,主震南西侧余震区长约27 km、北东侧长约10 km.余震分布在7~22 km深度区间,优势分布深度为9~14 km,序列平均深度约13 km,多数余震分布在主震上部.粗略估计的芦山地震震源体体积为37 km×16 km×16 km.（2）面应变As值统计显示,芦山地震序列以逆冲型地震占绝对优势,所占比例超过93%.序列主要受倾向NW、倾角约45°的近NE-SW向逆冲断层控制;部分余震发生在与上述主发震断层近乎垂直的倾向SE的反冲断层上;龙门山断裂带前山断裂可能参与了部分余震活动.P轴近水平且优势方位单一,呈NW-SE向,与龙门山断裂带南段所处区域构造应力场方向一致,反映芦山地震震源区主要受区域构造应力场控制,芦山地震是近NE-SW向断层在近水平的NW-SE向主压应力挤压作用下发生逆冲运动的结果.序列中6次非逆冲型地震均发生在主震震中附近,且主震震中附近P轴仰角变化明显,表明主震对其震中附近局部区域存在明显的应力扰动.（3）序列整体及不同震级段的应变花均呈NW向挤压白瓣形态,显示芦山地震震源区深部构造呈逆冲运动、NW向纯挤压变形.各震级段的应变花方位与形状一致,具有震级自相似性特征,揭示震源区深部构造运动和变形模式与震级无关.（4）不同深度的应变花形态以NW-NWW向挤压白瓣为优势,显示震源区构造无论是总体还是分段均以NW-NWW向挤压变形为特征.但应变花方位与形状随深度仍具有较明显的变化,可能反映了震源区构造变形在深度方向上存在分段差异.（5）芦山地震震源体尺度较小,且主震未发生在龙门山断裂带南段主干断裂上,南段长期积累的应变能未能得到充分释放,南段仍存在发生强震的危险.     

The April 24, 2013 Changning M s4.8 earthquake: a felt earthquake that occurred in Paleozoic sediment

The dense broadband seismic network provides more high-quality waveform that is helpful to improve constraint focal depth of shallow earthquake. Many shallow earthquakes occurring in sediment were regarded as induced events. In Sichuan basin, gas industry and salt mining are dependent on fluid injection technique that triggers microseismicity. We adopted waveform inversion method with regional records to obtain focal mechanism of an M _s4.8 earthquake at Changning. The result suggested that the Changning earthquake occurred at a ESE thrust fault, and its focal depth was about 3 km. The depth phases including teleseismic pP phase and regional sPL phase shows that the focal depth is about 2 km. The strong, short-period surface wave suggests that this event is a very shallow earthquake. The amplitude ratio between Rayleigh wave and direct S wave was also used to estimate the source depth of the mainshock. The focal depth (2–4 km) is far less than the depth of the sedimentary layer thickness (6–8 km) in epicentral region. It is close to the depth of fluid injection of salt mining, which may imply that this event was triggered by the industrial activity.     

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。     

一种低频地震事件的检测方法在汶川地震和芦山地震前的初步应用

本文发展了一种单台检测低频地震事件的方法, 并用其检测2008年汶川M_S8.0地震、 2013年芦山M_S7.0地震震前的低频事件。 使用汶川地震、 芦山地震前周边的宽频带台站数月的垂直向连续波形, 经过2~8 Hz带通滤波、 窗长为10 s的包络平滑、 窗长为20 min的中值滤波, 去除近场天然地震及远场大震与低频噪声的影响后, 发现这两个大地震前有少数台站在连续数天的时间内, 出现持续时间长(数十分钟到数小时)、 包络中值明显大于背景噪声的现象, 其波形记录及包络特征与非火山震颤(NVT)的波形记录及包络特征具有较好的相似性, 我们认为这是汶川地震和芦山地震前的疑似慢地震事件。 初步应用表明, 本文所用的方法对于从宽频带连续波形资料中提取NVT信号是可行的。     

Strong fast long-period waves in the Efpalio 2010 earthquake records: explanation in terms of leaking modes

The January 18, 2010, shallow earthquake in the Corinth Gulf, Greece (M _w  5.3) generated unusually strong long-period waves (periods 4–8 s) between the P and S wave arrival. These periods, being significantly longer than the source duration, indicated a structural effect. The waves were observed in epicentral distances 40–250 km and were significant on radial and vertical component. None of existing velocity models of the studied region provided explanation of the waves. By inverting complete waveforms, we obtained an 1-D crustal model explaining the observation. The most significant feature of the best-fitting model (as well as the whole suite of models almost equally well fitting the waveforms) is a strong velocity step at depth about 4 km. In the obtained velocity model, the fast long-period wave was modeled by modal summation and identified as a superposition of several leaking modes. In this sense, the wave is qualitatively similar to P long or Pnl waves, which however are usually reported in larger epicentral distances. The main innovation of this paper is emphasis to smaller epicentral distances. We studied properties of the wave using synthetic seismograms. The wave has a normal dispersion. Azimuthal and distance dependence of the wave partially explains its presence at 46 stations of 70 examined. Depth dependence shows that the studied earthquake was very efficient in the excitation of these waves just due to its shallow centroid depth (4.5 km).     

2013年4月20日四川芦山7.0级地震震源破裂特征

2013年4月20日四川芦山发生7.0级地震.本文运用反投影远震P波的方法研究了中心频率为1 Hz的芦山地震震源破裂特征.研究结果显示2013年芦山7.0级地震破裂长度约为20 km,震源破裂时间约为26 s.本文认为在芦山地震的开始阶段(0~4 s)震源的破裂是向震中位置两侧进行的.而芦山地震破裂的第二阶段(5~26 s)是单侧破裂.芦山地震最大能量释放区域位于震中以北.本文对比了运用相同方法研究的发生在同一断裂带上的2008年汶川地震震源破裂特征.发现2013年芦山地震和2008年汶川地震有三点相似之处,即,破裂主要沿北东走向的龙门山断裂带发展;最大能量释放区域没有位于震中;能量都是通过多次子事件来释放的,且第二次能量释放是最大能量释放.对比两次地震破裂区域,可以看出芦山地震的破裂区域是在2008年汶川地震破裂区域的西南端发展的.两次地震的破裂区域占了整个龙门山断裂带的三分之二.     

2013年南斯科舍海岭MW7.8地震的多点震源机制反演

2013年11月17日,在南极南奥克尼群岛北、南极板块与斯科舍板块之间发生了一次M_W7.8级地震（2013年南斯科舍海岭M_W7.8地震）,我们利用全球分布的长周期和宽频带地震记录反演确定了这次地震随时间和空间变化的震源机制,验证了提出的一种多点震源机制反演的新方法.首先利用长周期记录的W震相反演了这次地震的矩心矩张量解并利用体波提取了视震源时间函数,同时利用台阵反投影技术从宽频带记录中获得了这次地震的高频源的时空分布,然后基于矩心矩张量解、视震源时间函数以及高频源的时空分布,实现了采用新方法对2013年南斯科舍海岭M_W7.8地震的多点震源机制反演.矩心矩张量解表明,地震矩心在44.50°W/60.18°S,矩心深度19 km,半持续时间49 s,释放标量地震矩4.71×10²⁰ N·m,发震断层走向104°,倾角54°,滑动角8°.视震源时间函数清楚地揭示了地震矩随时间变化的方位依赖性,总体上可以将时间过程分为前60 s和后50 s两个阶段,但前60 s可细分为两次子事件.根据台阵反投影结果,这次地震为沿海沟从西到东的单侧破裂,破裂长度达311 km,可以分为5次子事件,能量释放的峰值点依次为13 s、30 s、51 s、64 s和84 s,平均破裂速度分别为0.6 km·s^-1、2.6 km·s^-1、2.3 km·s^-1、2.8 km·s^-1和3 km·s^-1.多点震源机制反演显示,5次子事件的矩震级分别为M_W7.57,M_W7.48,M_W6.80,M_W7.53和M_W7.08,半持续时间依次为21 s,17 s,6 s,16 s和8 s,走向分别为95°,105°,81°,98°和98°,倾角依次为57°,49°,86°,46°和64°,滑动角-9°,1°,-17°,13°和-4°.这些在震源机制、能量释放以及持续时间方面的变化都是当地构造和应力环境复杂性的反映.     

2019年西藏墨脱MS6.3地震震源参数及其构造意义

北京时间2019年4月24日04∶15,西藏自治区林芝市墨脱县发生了M_S6.3地震,该地震位于印度板块与欧亚板块俯冲碰撞的东北犄角地区,构造背景十分复杂.本研究基于我们在东喜马拉雅构造结地区架设的宽频带地震台站记录的近震波形数据,结合中国和国际地震台网的波形和到时资料,对该地震的震源位置、震源机制解和破裂过程进行了重新确定.结果显示,此次墨脱6.3级地震发生在（94.56±0.01°E,28.41±0.01°N）,震源深度为地表以下13.3±1.6（或海平面以下11.5±1.6）km.震源机制解走向/倾角/滑移角分别为202°/17°/20°,震源破裂较大的位置主要集中在初始破裂点NNE侧约5 km附近.结合其他地球物理和地质学资料,我们推测该地震位于主喜马拉雅逆冲断裂发生近90°突然偏转的大拐弯地区,桑构造结相对于其西侧南迦巴瓦构造结的西向俯冲和北向推挤是该地震发生的主要构造背景.     

四川芦山Ms7.0级强烈地震震源运动学特征

使用中国数字地震台网记录的区域宽频带波形,通过频率域和时间域多步反演,研究了2013年四川芦山“4·20”7.0级强烈地震的震源运动学特征.基于点源的震源机制解揭示：地震发震断层面参数分别为走向214°/倾角47°/滑动角96°,表现为一次高倾角的逆冲型事件.矩心在水平方向上位于震中（30.303°N/102.988°E）西南向约4.5 km,矩心深度约17 km.平均总标量地震矩M₀为1.16×10¹⁹ N·m,矩震级M_w约6.6.进一步模拟高达0.5 Hz高频波形,获得了芦山地震破裂过程图像,结果显示：此地震为一次不对称双侧破裂事件.破裂半径约15 km,整个破裂面积为706.7 km²,平均滑动量约0.231 m.破裂在8 s内释放了大多数能量.震后0~3 s内,破裂以孕震点为中心向四周同时扩展,3 s后,破裂表现出明显的方向性,主要向北北东扩展,导致位于震中北东向多数台站视破裂持续时间总体偏小,最小值为4 s.破裂约8 s后基本停止.