Relocation of the aftershock sequence of Milin MS6.9 earthquake in 2007 and spatio-temporal variation characteristics of b-value

HanJiadong; YangJiansi; WangWeiping

Abstract：The aftershock sequence of the Milin MS6.9 earthquake in Tibet in 2017 are relocated by double-difference algorithm in this paper. Based on the relocated results, the spatial distribution of b-value in the source region of Milin earthquake is obtained. Combining historical b-value data from previous researches, the temporal distribution of b-value in the studied area is also obtained. The relocation results show that the aftershock sequence of the Milin earthquake are distributed in NE?SE direction along the NE boundary of Indus-Yarlung Tsangpo big-turned suture and Bilu tectonic slice, most aftershocks are concentrated in 3?20 km depth. The temporal distribution of b-value shows before Milin earthquake b-value is lower than that in the year of 2008, indicating that the stress accumulation in the studied area is strong before Milin earthquake. After Milin earthquake, there was a step-rise of b-value, showing the releases of stress, and b-value tended to stable. b-value ranges in 0.52?1.35 in the source region of Milin earthquake, the b-value variation above the depth of 15 km is distributed along the east-west direction, and below 15 km along the NE?SW direction. Therefore, it is deduced that different b-value distribution represents different structure characteristics, i.e., the b-value variation of the shallow area is related to the degree of rupture in the source region, and the b-value variation of deep area reflects the lithology difference of different tectonic units.