2016年1月21日门源M_S 6.4级地震InSAR同震形变及发震构造研究

Study of the D-InSAR deformation field and seismotectonics of the Menyuan M_S 6.4 earthquake on January 21,2016

2016年1月21日青海省门源县发生M_S 6.4级地震,距离震中位置最近的已知断裂为位于其北侧7 km的冷龙岭断裂,该断裂晚第四纪以来主要表现为左旋走滑运动,局部兼具倾滑分量.但本次地震的震源机制解显示为逆冲型地震,与人们认知的冷龙岭断裂走滑运动性质有所差异.本研究利用Sentinel-1A数据获取了升降轨方向的形变场,形变场特征显示本次地震以逆冲为主,最大形变量在6 cm左右.以此数据为约束,采用两步法反演了发震断层参数,结果显示仅以InSAR数据为约束并不能唯一确定断层的倾向,因此本文对比了NE倾向和SW倾向等不同断层模型的反演结果,综合分析该地区的地质构造背景,认为SW倾向的断层模型更加合理,本次地震由冷龙岭北侧的弧形次生断层引起,发震断层面走向141°,倾向SW,倾角43°,平均滑动角为72.7°,最大滑动量为0.44 m,反演矩震级为M_W 6.0,震源深度10 km.该次生断层与冷龙岭断裂一起构成正花状构造,冷龙岭主干断层近直立插入基底,夹持部分形成隆起断块,推测本次地震是青藏高原向NW推挤生长,在压扭性作用下隆起断块的一种表现.

On January 21 st,2016,an M_S 6.4 earthquake hit Menyuan County,Qinghai province,China.The nearest known fault to the earthquake is the Lenglongling fault which is located approximately 7 km north of the epicenter.This fault has mainly shown sinistral strike-slip movement since the late Quaternary Period,with a localized dip-slip component.However,the focal mechanism indicates that it is a thrust earthquake,which is different from the well-known strike-slip feature of the Lenglongling fault.In this study,we obtained the ascending and descending orbit coseismic deformation field of the Menyuan earthquake using the Sentinel-1 A data.The characteristics of the deformation field indicate that this earthquake was a thrust-type earthquake,with a maximum Line-of-Sight(LOS)deformation of around 6 cm.Constrained by these InSAR data,based on the Okada Model we invert the fault distribution and source parameters through constructing fault model of different dip direction.The inversion results show that the seismic fault plane has a strike,dip direction and dip angle of approximately 141°,NE and 43°,respectively.The maximum slip distance is 0.44 m,and the average slip angle is 72.7°,with a magnitude of M_W 6.0 and focal depth of 10 km.By considering the geological structure of the seismogenic zone and the inversion results,we suggest that this earthquake was caused by the arc-shaped subfault located at the north side of the Lenglongling fault.This subfault,together with the Lenglongling fault,forms a normal flower structure.Therefore,we infer that this earthquake is the manifestation of a neotectonic movement,in which the bulging fault block is lifted further up under the compresso-shear action caused by the Tibetan Plateau pushing towards the northwest direction.