CUI TengFa,
CHEN XiaoBin,
ZHAN Yan et al
.2020.Characteristics of deep electrical structure and seismogenic structure beneath Anhui Huoshan earthquake area Chinese Journal of Geophysics(in Chinese),63(1): 256-269,doi: 10.6038/cjg2019M0458
安徽霍山地震区深部电性结构和发震构造特征
崔腾发, 陈小斌, 詹艳, 赵凌强, 刘钟尹
中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029
Characteristics of deep electrical structure and seismogenic structure beneath Anhui Huoshan earthquake area
CUI TengFa, CHEN XiaoBin, ZHAN Yan, ZHAO LingQiang, LIU ZhongYin
State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China
Abstract:Huoshan earthquake area is located in the northern margin of Dabie orogen, i.e., the contact zone between North China plate and Yangtze plate, where earthquakes are the most frequent and most concentrated in whole Dabie orogen and its surrounding area. A three-dimensional magnetotelluric array composed of 83 magnetotelluric stations covered the Huoshan earthquake area. Applying multi-grid method, impression and iterative reconstruction inversion technique and standard minimum structure nonlinear conjugate gradients method (NLCG), we inverted the array data and obtained the 3D electric structure beneath the area. The electrical structure reveals that mid-upper crust beneath North Dabie and North Huaiyang region is a high resistance area with the resistivity above 1000 Ωm and the mid-lower crust is a relatively low resistance area with tens of Ωm resistivity. The northwest-strike Xiaotian-Mozitan fault separate the North Huaiyang high resistivity layer from the North Dabie high resistivity layer. Fault dip is NE in the shallow and changes to SW in the deep. The northeast-strike Luoerling-Tudiling fault cuts through the high resistivity layer of North Dabie upper crust. Background seismicity relocated using the double difference earthquake location algorithm indicates:earthquakes mainly occurred in North Dabie and North Huaiyang high resistivity layer near the Luoerling-Tudiling fault, and were concentrated in the tectonic weak belt formed by early activities of Xiaotian-Mozitan fault. MS4.3 Huoshan earthquake has a deeper focal depth, and is located at a big electrical gradient zone in North Dabie high resistivity layer. Based on the above results, we think the primary seismogenic fault in Huoshan earthquake area is Luoerling-Tudiling fault. Fluid from mid-crustal conductive body below the fault propagates along the fault. It weakens the fault strength. The kinematic and deformation of the fault makes full use of the tectonic weak belt along Xiaotian-Mozitan fault. Since the existence of significant high resistivity layers in North Dabie belt and North Huaiyang belt, we consider there is a deep seismogenic environment beneath Huoshan earthquake area where earthquakes of magnitude above six are possible.
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