Deep Seismogenic Environment in the Southern Section of the Longmenshan Fault Zone on the Eastern Margin of the Tibetan Plateau and Lushan M_s 7.0 Earthquake

作     者：LI Dahu DING Zhifeng ZHAN Yan WU Pingping YE Qingdong 

作者机构：Institute of GeophysicsChina Earthquake Administration Earthquake Administration of Sichuan Province Institute of GeologyChina Earthquake Administration 

出 版 物：《Acta Geologica Sinica(English Edition)》 (地质学报（英文版）)

年 卷 期：2015年第89卷第2期

页      面：519-530页

核心收录：

学科分类：070801[理学-固体地球物理学] 07[理学] 0708[理学-地球物理学] 

基　　金：supported by China earthquake scientific array exploration-northern section of North South seismic belt (20130811) National Natural Science Foundation of China (41474057) Science for earthquake Resllience of China Earthquake Administration (XH15040Y) 

主　　题：The Longmenshan fault zone Lushan earthquake the three-dimensional velocitystructure the apparent magnetization inversion magnetotelluric sounding 

摘      要：The 2,026 earthquake events registered by the Sichuan regional digital seismic network and mobile seismic array after the April 20th, 2013 Lushan earthquake and 28,188 pieces of data were selected to determine direct P waves arrival times. We applied the tomographic method to inverse the characteristics of the velocity structure for the three-dimensional （3D） P wave in the mid-upper crust of the seismic source region of the Lushan earthquake. The imaging results were combined with the apparent magnetization inversion and magnetotelluric （MT） sounding retest data to comprehensively study the causes of the deep seismogenic environment in the southern section of the Longmenshan fault zone and explore the formation of the Lushan earthquake. Research has shown that there are obvious differences in velocity structure and magnetic distribution between the southern and northern sections of the Longmenshan fault zone. The epicenter of the Lushan earthquake is located near the boundary of the high and low-velocity anomalies and favorable for a high-velocity section. Moreover, at the epicenter of the Lushan earthquake located on the magnetic dome boundary of Ya＇an, the development of high velocity and magnetic solid medium favors the accumulation and release of strain energy. Low- velocity anomalies are distributed underneath the are of seismogenic origin, The inversion results of the MT retest data after the April 20th Lushan earthquake also indicate that there a high-conductor anomaly occurs under the area of seismogenic origin of the Lushan earthquake, Therefore, we speculated that the presence of a high-conductivity anomaly and low-velocity anomaly underneath the seismogenic body of the Lushan earthquake could be related to the existence of fluids. The role of fluids caused the weakening of the seismogenic layer inside the mid-upper crust and resulted in a seismogenic fault that was prone to rupture and pIayed a triggering role in the Lushan earthquake.