Dozens of 】M5, hundreds of 】M4, and much more 】M3 aftershocks occurred after the 2008/05/12 Wenchuan earthquake, which were well recorded by permanent and portable seismic stations. After relocated with P arrival, ...Dozens of 】M5, hundreds of 】M4, and much more 】M3 aftershocks occurred after the 2008/05/12 Wenchuan earthquake, which were well recorded by permanent and portable seismic stations. After relocated with P arrival, the 】M3 aftershocks show two trends of distribution, with most of the aftershocks located along the north-east strike consistent with Longmenshan fault system, yet there is a north-west trend around the epicenter. It seems that substantially more aftershocks occur in regions with crystalline bedrocks. Then we collected waveform data from National Digital Seismograph Network and regional seismograph network of China, and employed 'Cut and Paste' method to obtain focal mechanisms and depths of the big aftershocks (M≥5.6). While most of those aftershocks show thrust mechanism, there are some strike slip earthquakes in the northern-most end of the rupture. Focal mechanisms show that the events located on the southern part of central Beichuan-Yingxiu Fault (BY) are mainly thrust earthquakes, which is consistent with initial mechanism of the main shock rupture. In the north part the aftershocks along the BY are also dominated by thrust slip, which is quite different from the right slip rupture of the main shock. Around Qingchuan-Pingwu Fault, the focal mechanisms are dominated by right-slip rupture with large depths (~18 km). So we suspected that in the north part the main shock might rupture on two faults: Beichuan Fault and Qingchuan-Pingwu Fault. The complex pattern of aftershock mechanisms argues for presence of a complicated fault system in the Longmenshan area.展开更多
Using the Cut And Paste(CAP)method,we invert the focal mechanism of 38 moderate earthquakes(M_(S)≥3.0)recorded by Yunnan seismic network and analyze the corresponding focal mechanism consistency based on the minimum ...Using the Cut And Paste(CAP)method,we invert the focal mechanism of 38 moderate earthquakes(M_(S)≥3.0)recorded by Yunnan seismic network and analyze the corresponding focal mechanism consistency based on the minimum spatial rotation angle.Our results indicate that the M_(S)6.4 mainshock is induced by a lateral strike slip fault(with a rake angle of~-165°)and a little normal-faulting component event along a nearly vertical plane(dipping angle~79° and strike~138°).Combining our results with high resolution catalog,we argue that the seismogenic fault of this earthquake sequence is a secondary fault western to the major Weixi-Qiaohou-Weishan fault.The focal mechanism evolution can be divided into three periods.During the first period,the foreshock sequence,the focal mechanism consistency is the highest(KA<36°);during the second period which is shortly after the mainshock,the focal mechanism shows strong variation with KA ranging from 8° to 110°;during the third period,the seismicity becomes weak and the focal mechanism of the earthquakes becomes more consistent than the second period(18°<KA<73°).We suggest that the KA,to some extent,represents the coherence between local tectonic stress regime and the stress state of each individual earthquake.Furthermore,high focal mechanism consistency and high linearity of seismic distribution may serve as indicators for the identification of foreshock sequence.展开更多
In this article, we have inverted local broadband waveform data to determine the focal mechanism of the 2011 MS4.8 Anqing earthquake. Our results show that the best double couple solution of the MS4.8 event is 16°...In this article, we have inverted local broadband waveform data to determine the focal mechanism of the 2011 MS4.8 Anqing earthquake. Our results show that the best double couple solution of the MS4.8 event is 16°, 74° and 120° for strike, dip and rake angles of one nodal plane respectively, and 131°, 33°, 30° for the other nodal plane. The estimated focal depth is about 3km. Both strikes of the two nodal planes differ significantly to the strike of Susong-Zongyang fault, along which seismic activity has been at a low level since the Late Quaternary. This implies that this earthquake may not have occurred on the Susong-Zongyang fault, and we infer that a buried fault with strike of NNE may be the seismogenic structure of this event.展开更多
利用湖北与重庆区域台网共9个台的宽频带数字地震记录,采用CAP法(Cut and Paste Method)反演了湖北巴东2013年12月16日MS5.1地震震源机制解,其最佳双力偶解为节面I:走向166°,倾角82°,滑动角41°;节面Ⅱ:走向69°,倾角...利用湖北与重庆区域台网共9个台的宽频带数字地震记录,采用CAP法(Cut and Paste Method)反演了湖北巴东2013年12月16日MS5.1地震震源机制解,其最佳双力偶解为节面I:走向166°,倾角82°,滑动角41°;节面Ⅱ:走向69°,倾角49°,滑动角169°;最佳震源深度主要集中分布在5.5km附近。分析认为此次地震的发震断层为带有逆冲成分的走滑性质断层,主压应力P轴近EW向,主张应力轴近NS向。余震序列主要呈EW分布,少部分呈NS方向分布,较大余震的发震破裂滑动类型以正走滑型的居多,其次为逆倾滑型及逆走滑型。结合7次较大余震的机制解判断,近EW向节面为发震断层。展开更多
基金Supported by Knowledge Innovation Project of Chinese Academy of Sciences (Grant Nos. KZCX3-SW-153, KZCX2-YW-116-1)National Natural Science Foundation of China (Grant No. 40604004)National Basic Technology R & D Program (GrantNo. 2006BAC01B02-01-02)
文摘Dozens of 】M5, hundreds of 】M4, and much more 】M3 aftershocks occurred after the 2008/05/12 Wenchuan earthquake, which were well recorded by permanent and portable seismic stations. After relocated with P arrival, the 】M3 aftershocks show two trends of distribution, with most of the aftershocks located along the north-east strike consistent with Longmenshan fault system, yet there is a north-west trend around the epicenter. It seems that substantially more aftershocks occur in regions with crystalline bedrocks. Then we collected waveform data from National Digital Seismograph Network and regional seismograph network of China, and employed 'Cut and Paste' method to obtain focal mechanisms and depths of the big aftershocks (M≥5.6). While most of those aftershocks show thrust mechanism, there are some strike slip earthquakes in the northern-most end of the rupture. Focal mechanisms show that the events located on the southern part of central Beichuan-Yingxiu Fault (BY) are mainly thrust earthquakes, which is consistent with initial mechanism of the main shock rupture. In the north part the aftershocks along the BY are also dominated by thrust slip, which is quite different from the right slip rupture of the main shock. Around Qingchuan-Pingwu Fault, the focal mechanisms are dominated by right-slip rupture with large depths (~18 km). So we suspected that in the north part the main shock might rupture on two faults: Beichuan Fault and Qingchuan-Pingwu Fault. The complex pattern of aftershock mechanisms argues for presence of a complicated fault system in the Longmenshan area.
基金sponsored by Earthquake monitoring, forecasting, and scientific research project of China Earthquake Administration(3JH-2021046)Sub-projects of The National Key Research and Development Program of China(2018YFC150330303)the Academician Workstation of Chen Yong of Yunnan Province (2014IC007).
文摘Using the Cut And Paste(CAP)method,we invert the focal mechanism of 38 moderate earthquakes(M_(S)≥3.0)recorded by Yunnan seismic network and analyze the corresponding focal mechanism consistency based on the minimum spatial rotation angle.Our results indicate that the M_(S)6.4 mainshock is induced by a lateral strike slip fault(with a rake angle of~-165°)and a little normal-faulting component event along a nearly vertical plane(dipping angle~79° and strike~138°).Combining our results with high resolution catalog,we argue that the seismogenic fault of this earthquake sequence is a secondary fault western to the major Weixi-Qiaohou-Weishan fault.The focal mechanism evolution can be divided into three periods.During the first period,the foreshock sequence,the focal mechanism consistency is the highest(KA<36°);during the second period which is shortly after the mainshock,the focal mechanism shows strong variation with KA ranging from 8° to 110°;during the third period,the seismicity becomes weak and the focal mechanism of the earthquakes becomes more consistent than the second period(18°<KA<73°).We suggest that the KA,to some extent,represents the coherence between local tectonic stress regime and the stress state of each individual earthquake.Furthermore,high focal mechanism consistency and high linearity of seismic distribution may serve as indicators for the identification of foreshock sequence.
基金supported by the China Earthquake Administration as a work Assignment for Seismic Situation Tracing for Earthquake Forecast and Prediction (2011020104)
文摘In this article, we have inverted local broadband waveform data to determine the focal mechanism of the 2011 MS4.8 Anqing earthquake. Our results show that the best double couple solution of the MS4.8 event is 16°, 74° and 120° for strike, dip and rake angles of one nodal plane respectively, and 131°, 33°, 30° for the other nodal plane. The estimated focal depth is about 3km. Both strikes of the two nodal planes differ significantly to the strike of Susong-Zongyang fault, along which seismic activity has been at a low level since the Late Quaternary. This implies that this earthquake may not have occurred on the Susong-Zongyang fault, and we infer that a buried fault with strike of NNE may be the seismogenic structure of this event.
文摘利用湖北与重庆区域台网共9个台的宽频带数字地震记录,采用CAP法(Cut and Paste Method)反演了湖北巴东2013年12月16日MS5.1地震震源机制解,其最佳双力偶解为节面I:走向166°,倾角82°,滑动角41°;节面Ⅱ:走向69°,倾角49°,滑动角169°;最佳震源深度主要集中分布在5.5km附近。分析认为此次地震的发震断层为带有逆冲成分的走滑性质断层,主压应力P轴近EW向,主张应力轴近NS向。余震序列主要呈EW分布,少部分呈NS方向分布,较大余震的发震破裂滑动类型以正走滑型的居多,其次为逆倾滑型及逆走滑型。结合7次较大余震的机制解判断,近EW向节面为发震断层。
