尼泊尔M_W7.8地震InSAR同震形变场及断层滑动分布

采用DInSAR技术和欧空局2014年新发射的Sentinel-1A/IW数据,获取了2015年4月25日尼泊尔M_W7.8地震的InSAR同震形变场.所用InSAR数据扫描范围东西长约500 km,南北宽约250 km,覆盖了整个变形区域,揭示了形变场的全貌及其空间连续变化形态.此次地震造成的地表形变场总体呈现为中部宽两端窄的纺锤形,从震中向东偏南约20°方向延伸,主要形变区东西长约160 km,南北宽约110 km,由规模较大的南部隆升区和规模较小的北部沉降区组成,南部最大LOS向隆升量达1.1 m,北部最大LOS向沉降量约在0.55 m.在隆升和沉降区之间干涉纹图连续变化,没有出现由于形变梯度过大或地表破裂而导致的失相干现象,表明地震断层未破裂到地表.基于InSAR形变场和部分GPS观测数据,利用弹性半空间低倾角单一断层面模型进行了滑动分布单独反演和联合反演,三种反演结果均显示出一个明显的位于主震震中以东的滑动分布集中区,向外围衰减很快,主要滑动发生于地下7~23 km的深度范围内.InSAR单独反演的破裂范围,特别是东西向破裂长度大于GPS单独反演的破裂长度,而InSAR单独反演的最大滑动量则低于GPS单独反演的滑动量.因此认为联合反演结果更为可靠.联合反演的破裂面长约150 km,沿断层倾向宽约70 km,最大滑移量达到4.39 m,矩震级为M_W7.84,与之前用地震波数据和GPS数据反演的结果一致.

Coseismic deformation field of the Nepal MS8.1 earthquake from Sentinel-1A/InSAR data and fault slip inversion

We processed and analyzed the Sentinel-1A/IW data by InSAR technology and acquired the surface deformation fields caused by Nepal M_S8.1 earthquake occurred on 25 Apr. 2015. The used data cover an area of 500 km×250 km. The result shows that the whole deformation field caused by this event looks like a spindle shape and extends from the epicenter to a direction of about east by south 20°. Main deformation scope is about 160 km×110 km, long in east-west direction. The deformation field consists of a great uplift area and a weak subsidence area, the maximum rising value reaches about 1.1 m in LOS direction, and the maximum Settlement displacement is about 0.55 m in LOS. In the whole deformation region, including the transition area between uplift and subsidence, the fringes and unwrapped displacement are distributed continually, no incoherence belt can be found, which indicates the seismic fault rupture not reaching ground surface. Based on InSAR deformation field and GPS observation data, we carried out the slip distribution inversion alone and jointly by using a fault model with single fault plane and low dip angle. Three kinds of inversion results all showed an obvious slip concentrated area located in the east of the epicenter of the main shock,the main sliding occurred in the depth range of 7 km to 23 km. The rupture range from InSAR inversion alone, in particular, the rupture length is greater than the length of the GPS inversion, while the maximum slip of InSAR inversion is lower than that of GPS alone. The rupture length of the joint inversion is about 150 km, and the rupture width in fault dip direction is about 70 km, the maximum slip is about 4.39 m, the moment magnitude is M_W7.84, consistent with previous results from seismic data and GPS data inversion. The joint inversion with complementary advantages is more reliable.