Source mechanism of strong aftershocks (Ms⩾5.6) of the 2008/05/12 Wenchuan earthquake and the implication for seismotectonics
Source mechanism of strong aftershocks (Ms⩾5.6) of the 2008/05/12 Wenchuan earthquake and the implication for seismotectonics
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DOI：
10.1007/s11430-009-0074-3
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发表时间：
2009-06
期刊：
影响因子：
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通讯作者：
Yong Zheng;Hong-Sheng Ma;Jian Lü;S. Ni;Yingchun Li;S. Wei
中科院分区：
文献类型：
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作者：
Yong Zheng;Hong-Sheng Ma;Jian Lü;S. Ni;Yingchun Li;S. Wei
2008年5月12日汶川大地震后发生了数十次> 5级、数百次> 4级和更多次> 3级余震，这些余震被固定和移动地震台站记录得很好。P波定位后，>M3级余震有两种分布趋势，大部分余震沿着与龙门山断裂系统一致的北东走向，但在震中附近有北西走向。似乎更多的余震发生在有结晶岩的地区。然后，利用国家数字地震台网和中国区域地震台网的波形资料，采用剪切粘贴法，得到了这次大余震（M ≥ 5.6）的震源机制和震源深度。虽然这些余震大多表现为逆冲机制，但在破裂的最北端也有一些走滑地震。震源机制解表明，位于北川-映秀断裂中部（BY）南部的地震以逆冲地震为主，这与主震破裂的初始机制一致。在北半球，沿北东向沿着的余震也以逆冲滑动为主，这与主震的右滑破裂有很大的不同。在青川-平武断裂带附近，震源机制以深达18 km的右行走滑破裂为主。因此，我们推测北部主震可能在北川断裂和青川-平武断裂上破裂。复杂的余震机制模式表明龙门山地区存在复杂的断裂系统。
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.