Study on Dynamic Characteristics of Fault Locking in the Eastern Boundary of the Sichuan-Yunnan Rhombic Block

Abstract:

By using the GPS horizontal velocity field of 1999～2007, 2009～2013 and the negative dislocation model of DEFNODE, we inverted for spatial fault locking in the eastern boundary of the Sichuan-Yunnan rhombic block which contains four major fault zones named Xianshuihe, Anninghe, Zemuhe and Xiaojiang before and after the Wenchuan earthquake. We analyzed the seismic potential sections of the fault zones combining with the spatial distribution of b-values and the spatial-temporal pattern of earthquake rupture. The results show that before the Wenchuan earthquake the southernmost segment of Xianshuihe fault is completely locked to 25km, the middle-southern segment is tightly locked from the surface to 10-15km depth, and the middle-northern segment is in creeping state. The southernmost segment of Anninghe fault is weakly locked, while the locking depth of other segments are between 10km to 15km. Zemuhe fault is completely locked except the locking fraction of the southernmost segment being about 0.8. Xiaojiang fault is weakly locked in four regions including the south of Qiaojia, the south of Dongchuan, the neighborhood of Yiliang and the north of Huaning, while other segments are tightly locked. The fault locking inverted by GPS velocity between 10 years indicates that the Daofu-Bamei segment of Xianshuihe fault, the middle segment of Anninghe fault, the middle-northern segment of Zemuhe fault, the northern segment of Xiaojiang fault around Dongchuan, and the Huaning-Jianshui segment of Xiaojiang fault are seismic potential segments, which is consistent with the potential segments indicated by seismic gaps along the fault zones of geological scale and the spatial distribution of b-values during 30 years. The velocity distribution far and near fault zone and the block movement changed after the Wenchuan earthquake, and such adjustment of regional crustal movement made the fault locking state inverted by the negative dislocation model change.

Keywords: The eastern boundary of the Sichuan-Yunnan rhombic block; The Wenchuan earthquake; Negative dislocation inversion of DEFNODE; Fault locking; Slip deficit