2016年门源M_S6.4强震的发震构造及其对“天祝地震空区”的影响

Seismogenic Structure of the 2016 M_S6.4 Menyuan Earthquake and Its Effect on the Tianzhu Seismic Gap

在综合分析区域活动断裂活动特征、震源机制解、余震精定位等资料的基础上,结合GPS观测数据,推断冷龙岭断裂倾向NE,而非部分早期研究推测的倾向SW。考虑到2016年和1986两次门源MS6.4强震相似的震源机制与冷龙岭断裂的位置关系以及冷龙岭断裂倾向NE等事实,可推测判定这两次强震的发震构造应为冷龙岭断裂;冷龙岭断裂处于祁连-海原活动断裂系内著名的破裂空段"天祝地震空区"的西段,该地震空区内部的金强河断裂可能为一个次级的地震空区,未来存在6级左右强震危险;冷龙岭断裂目前处于比较活跃的状态,说明该段的应力、应变积累水平较高,未来存在大震可能,且不排除冷龙岭断裂与金强河断裂同时破裂的可能性。

On January 21, 2016, a strong earthquake with a magnitude of Ms6. 4 occurred at Me- nyuan, Qinghai province, China. In almost the same region, another strong earthquake occurred in 1986, with similar magnitude and focal mechanism. Based on comprehensive analysis of regional active faults, focal mechanism solutions, precise locations of aftershocks, as well as GPS crustal deforma- tion, we infer that the Lenglongling active fault dips NE rather than SW as was suggested by previous studies. Considering the facts that the 2016 and 1986 Ms6.4 Menyuan earthquakes are closely located with similar focal mechanisms, that both quakes are on the north side of the Lenglongling fault and adjacent to the fault, and that the fault is dipping in a NE direction, we suggest that the fault is the seismogenic structure of the two events. The Lenglongling fault, as the western segment of the well- known Tianzhu seismic gap in the Qilian-Haiyuan active fault system, is in a relatively active state with frequent earthquakes in recent years, implying a high level of strain accumulation and a high po- tential for a future major event. It is also possible that the Lenglongling fault and the adjacent Jin- qianghe fault in the Tianzhu seismic gap, will rupture simultaneously in the future.