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 arr...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
At 5: 39 AM on 24 June 2017, a huge landslide-debris avalanche occurred on Fugui Mountain at Xinmo village, Diexi town, Maoxian county, Sichuan province, China. The debris blocked the Songpinggou River for about 2 km,...At 5: 39 AM on 24 June 2017, a huge landslide-debris avalanche occurred on Fugui Mountain at Xinmo village, Diexi town, Maoxian county, Sichuan province, China. The debris blocked the Songpinggou River for about 2 km, resulting in a heavy loss of both human lives and properties(10 deaths, 3 injuries, 73 missing, and 103 houses completely destroyed). The objectives of this paper are to understand the overall process and triggering factors of this landslide and to explore the affecting factors for its long term evolution before failure. Post event surveys were carried out the day after the landslide occurrence. Information was gathered from literature and on-site investigation and measurement. Topography, landforms, lithology, geological setting, earthquake history, meteorological and hydrological data of the area were analysed. Aerial photographs and other remote sensing information were used for evaluation and discussion. Eye witnesses also provided a lot of helpful information for us to understand the process of initiation, development and deposition. The depositional characteristics of the moving material as well as the traces of the movement,the structural features of the main scarp and the seismic waves induced by the slide are presented and discussed in detail in this paper. The results show that the mechanism of the landslide is a sudden rupture of the main block caused by the instability of a secondary block at a higher position. After the initiation, the failed rock mass at higher position overloaded the main block at the lower elevation and collapsed in tandem. Fragmentation of the rock mass occurred later, thus forming a debris avalanche with high mobility. This landslide case indicates that such seismic events could influence geological hazards for over 80 years and this study provides reference to the long term susceptibility and risk assessment of secondary geological hazards from earthquake.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financially supported by the National Basic Reareach program of China (973 program, Grant No. 2013CB733201)Key Research Program of Frontier Sciences, CAS (Grant No. QYZDY-SSW-DQC006)the “Hundred Talents” program (SU Li-jun) of Chinese Academy of Sciences (CAS)
文摘At 5: 39 AM on 24 June 2017, a huge landslide-debris avalanche occurred on Fugui Mountain at Xinmo village, Diexi town, Maoxian county, Sichuan province, China. The debris blocked the Songpinggou River for about 2 km, resulting in a heavy loss of both human lives and properties(10 deaths, 3 injuries, 73 missing, and 103 houses completely destroyed). The objectives of this paper are to understand the overall process and triggering factors of this landslide and to explore the affecting factors for its long term evolution before failure. Post event surveys were carried out the day after the landslide occurrence. Information was gathered from literature and on-site investigation and measurement. Topography, landforms, lithology, geological setting, earthquake history, meteorological and hydrological data of the area were analysed. Aerial photographs and other remote sensing information were used for evaluation and discussion. Eye witnesses also provided a lot of helpful information for us to understand the process of initiation, development and deposition. The depositional characteristics of the moving material as well as the traces of the movement,the structural features of the main scarp and the seismic waves induced by the slide are presented and discussed in detail in this paper. The results show that the mechanism of the landslide is a sudden rupture of the main block caused by the instability of a secondary block at a higher position. After the initiation, the failed rock mass at higher position overloaded the main block at the lower elevation and collapsed in tandem. Fragmentation of the rock mass occurred later, thus forming a debris avalanche with high mobility. This landslide case indicates that such seismic events could influence geological hazards for over 80 years and this study provides reference to the long term susceptibility and risk assessment of secondary geological hazards from earthquake.
