2008年新疆乌恰Mw6.7地震震源机制与形变特征的InSAR研究

2008年10月5日新疆乌恰M_w6.7级地震发生在南天山、帕米尔高原及塔里木盆地交汇地带，基于地震波反演的震源机制解确定的震源深度存在较大差异.本文利用日本ALOS卫星的PALSAR图像，获得了本次地震的同震形变场，基于卫星视线向（LOS）和方位向（Azimuth）的形变，采用均匀弹性半无限位错模型和有界最小二乘（BVLS）算法，以网格矩形位错元法对发震断层的几何产状、滑移及分布进行了估算，结果表明本次地震以逆断破裂为主，断层面上最大位错量接近3.4 m，形变中心位于73.8040°E，39.5335°N，深度约5 km，震级估算为M_w6.6；地震发生在走向46°，倾角48°的断层上，发震断层长30 km，宽14 km，闭锁深度9 km，符合该地区浅源地震多发的构造特点，发震断层为乌合沙鲁断裂带.InSAR反演的滑移形变主要集中于地下2~7 km，表明乌恰地震为浅源地震，可能与该断层附近历史地震未完全释放的残余应力积累有关.同时，InSAR反演的断层位错分布呈现双破裂特征，震级分别为M_w6.5和M_w6.1，可能与本次地震的主震和余震相对应，也可能是由主震激发而产生的两组破裂.

Study on the focal mechanism and deformation characteristics for the 2008 Mw6.7 Wuqia earthquake,Xinjiang by InSAR

A magnitude M_w6.7 earthquake took place in the joint area of the southern Tienshan Mountain, the Pamir Plateau and the Tarim Basin on October 5, 2008. The focal mechanism of this event is investigated by many scientists and organizations, but the epicenter depth is much different. We use PALSAR images from the ALOS satellite to derive the coseismic deformation field. The geometry of rectangular dislocation elements and its slip distributions are inverted based on InSAR-derived LOS and Azimuth coseismic changes by using a half-space homogenous elastic model and Bounded Variables Least Squares (BVLS) algorithm. The results indicate that the moment magnitude of Wuqia earthquake is about M_w6.6 and the rupture is dominated by an inverse fault with a maximum slip ~3.4 m at 73.8040°E, 39.5335°N and with depth of 5 km. Most displacements are confined to 2~7 km underground. The rupture plane is about 30 km×14 km with strike N46°E and dip 48° to NE. The shallow focal depth is possibly resulted from the unreleased stress accumulation from history earthquakes around the seismic fault. At the same time, slip pattern implies that the rupture is composed by two point source models with magnitude M_w6.5 and M_w6.1, respectively, which has a good correspondence with main shock and aftershock of Wuqia earthquake. Alternatively, the slip pattern may be caused by two ruptures of the main shock.