摘要Using the double-difference relocation algorithm, we relocated the 20 April 2013 Lushan, Sichuan, earthquake (MS7.0), and its 4,567 aftershocks recorded during the period between 20 April and May 3, 2013. Our results showed that most aftershocks are relocated between 10 and 20 km depths, but some large aftershocks were relocated around 30 km depth and small events extended upward near the surface. Vertical cross sections illustrate a shovel-shaped fault plane with a variable dip angle from the southwest to northeast along the fault. Furthermore, the dip angle of the fault plane is smaller around the mainshock than that in the surrounding areas along the fault. These results suggest that it may be easy to generate the strong earthquake in the place having a small dip angle of the fault, which is somewhat similar to the genesis of the 2008 Wenchuan earthquake. The Lushan mainshock is underlain by the seismically anomalous layers with low-VP, low-VS, and high-Poisson’s ratio anomalies, possibly suggesting that the fluid-filled fractured rock matrices might significantly reduce the effective normal stress on the fault plane to bring the brittle failure. The seismic gap between Lushan and Wenchuan aftershocks is suspected to be vulnerable to future seismic risks at greater depths, if any.
Abstract：Using the double-difference relocation algorithm, we relocated the 20 April 2013 Lushan, Sichuan, earthquake (MS7.0), and its 4,567 aftershocks recorded during the period between 20 April and May 3, 2013. Our results showed that most aftershocks are relocated between 10 and 20 km depths, but some large aftershocks were relocated around 30 km depth and small events extended upward near the surface. Vertical cross sections illustrate a shovel-shaped fault plane with a variable dip angle from the southwest to northeast along the fault. Furthermore, the dip angle of the fault plane is smaller around the mainshock than that in the surrounding areas along the fault. These results suggest that it may be easy to generate the strong earthquake in the place having a small dip angle of the fault, which is somewhat similar to the genesis of the 2008 Wenchuan earthquake. The Lushan mainshock is underlain by the seismically anomalous layers with low-VP, low-VS, and high-Poisson’s ratio anomalies, possibly suggesting that the fluid-filled fractured rock matrices might significantly reduce the effective normal stress on the fault plane to bring the brittle failure. The seismic gap between Lushan and Wenchuan aftershocks is suspected to be vulnerable to future seismic risks at greater depths, if any.
基金资助:the National Natural Scientific Foundation of China (41274059 and 40974021), Beijing Natural Scientific Foundation (8122039 and 8092028) to J. Lei, and Special Project for Basic Scientific Research (ZDJ2013-12) to G. Zhang
通讯作者:
Jianshe Lei
E-mail: leijs@eq-icd.cn
引用本文:
Jianshe Lei, Guangwei Zhang, Furen Xie. The 20 April 2013 Lushan, Sichuan, mainshock, and its aftershock sequence: tectonic implications[J]. 《地震学报》英文版, 2014, 27(1): 15-25.
Jianshe Lei, Guangwei Zhang, Furen Xie. The 20 April 2013 Lushan, Sichuan, mainshock, and its aftershock sequence: tectonic implications. Earthquake Science, 2014, 27(1): 15-25.
