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focal mechanisms of the Lushan earthquake sequence and spatial variation of the stress field

Science China Earth Sciences 2015年第4期58卷 1148-1158页

作者： LUO Yan ZHAO Li ZENG XiangFang GAO Yuan Institute of Earthquake Science China Earthquake Administration Institute of Earth Sciences Academia Sinica Key Laboratory of Computational Geodynamics Chinese Academy of Sciences

Using broadband seismic records from regional networks, we determined the focal mechanisms and depths of 37 earthquakes in the 2013 M7.0 Lushan earthquake sequence(3.4≤Mw≤5.1) by fitting the three-component waveform data. The results show that the earthquakes are predominantly thrust events, with occasional strike-slip mechanisms. Most earthquakes occurred at depths of 10–20 km. We derived the regional distribution of the average stress field in this area using the damped linear inversion method and the focal mechanisms obtained in this study. The inversion results suggest that the Lushan region and the adjacent area are mostly under compression. The orientations of the maximum principal axes trend NW-SE, with some local differences in the stress distribution at different depths. Compared with the distribution of the stress field in the Wenchuan earthquake area, the stress field in the southwest section of the Longmenshan Fault zone(LFZ) share similar characteristics, predominantly thrust faulting with a few strike-slip events and the maximum compression axes being perpendicular to the LFZ.

关键词： Lushan earthquake focal mechanisms stress field aftershock sequence

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Consistent Distribution of Stress before Strong Earthquake from focal mechanisms

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Earthquake Research in China 2010年第4期24卷 415-422页

作者： Zeren Zhima Diao Guiling Li Zhixiong Institute of Earthquake Science China Earthquake Administration Beijing 100036 China Earthquake Administration of Hebei Province Shijiazhuang 050021 China

At some stage of a strong earthquake preparation, the focal mechanisms of small earthquakes have roughly the same direction with the tectonic stress field. According to this feature, we define the angle between P, B and T axis of focal mechanisms and the three stress axes of tectonic stress field as the consistency parameter a in studying the dynamic changes of stress fields in earthquake preparation areas. We mainly analyze the changes of the consistency parameter a of the Mw8. 3 Knril island arc earthquake and the Mw8. 4 Peru earthquake. Our study shows that before the strong earthquakes, the earthquake area saw a low consistency, and the focal mechanisms of a series of small earthquakes had small differences in the directions with the tectonic stress field, which means the foreshocks were under the control of the stress field. On the other hand, a higher consistency means the focal mechanisms of their aftershocks are scattered and have big differences in the directions with the tectonic field, which indicate that the control of background stress field starts weakening.

关键词： focal mechanisms The consistency Kuril Island Peru Stress field

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Regional stress field around the Taigu fault zone in Shanxi Province,China

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Earthquake Science 2015年第5期28卷 333-345页

作者： Bin Li Zihong Li Mathilde B.S?rensen Reidar L?vlie Liqiang Liu Kuvvet Atakan Earthquake Administration of Shanxi Province Department of Earth Science University of Bergen State Key Laboratory of Earthquake Dynamics Institute of GeologyChina Earthquake Administration

A comprehensive study on regional stress field around the Taigu fault zone in Shanxi Province, China, was performed in this study. To get a better understanding of the present-day stress status in this area, 31 focal mecha- nisms of ML 〉3 earthquakes since 1965 were compiled, and the best stress tensor was then inverted based on the database. Additionally, magnetic fabrics along the Taigu fault zone were investigated to get an indication of the regional stress field in the past. Our results show that the present-day stress field around the Taigu fault zone is characterized by astable NW-SE extension with a strike- slip component, consistent with the geological surveys and recent GPS data. Results from magnetic fabrics indicate that the orientations of principal stress axes from magnetic fabrics of sedimentary rocks in Neogene coincide to the orientations of principal stress axes from focal mecha- nisms. The south segment of the Taigu fault displays more complicated magnetic fabrics and more activity of mod- erate earthquakes. It is connected with the Mianshan west fault and intersects with NW-SE striking Fenyang fault and the north fault of the Lingshi uplift at the south edge of Taiyuan basin. This may be the area needing more atten- tion in terms of seismic risk along the Taigu fault.

关键词： focal mechanisms Stress tensor inversion Magnetic fabric Taigu fault Shanxi rift

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