基于InSAR的青海大柴旦地震三维同震形变场获取与震源特征分析

Three-dimensional co-seismic deformation of the Da Qaidam,Qinghai earthquakes derived from D-InSAR data and their source features

本文利用Envisat ASAR的升、降轨和宽幅数据,通过基于先验知识的最小二乘迭代逼近获取大柴旦2次地震的地表三维同震形变.结果表明,2008年MW6.3地震垂直向形变主要发生在断层南盘,以隆升形变为主,最大隆升量约10cm,北盘沉降量小于等于-1cm.东西向形变在南盘呈向东运动的特征,最大运动量约4cm,北盘向西运动,最大运动量约为-2cm.2009年MW5.8地震垂直向形变显示断层南盘抬升的特征,最大抬升量约27cm,北盘最大沉降量约-3cm.东西向形变表现为南盘向东运动,最大约10cm,北盘向西运动,约为-4cm.可以看出这两次地震均表现为逆冲为主,兼少量左旋走滑的震源特征.视线向结果无法判定同震形变的少量走滑特征,而地表三维分量可以有效地识别出少量左旋还是右旋走滑的震源特性.本文以视线向、垂直向、东西向形变量作为约束条件,利用Okada模型正演了2008年地震同震三维形变场.结果显示,采用逆冲兼少量左旋走滑的发震断层参数,视线向、垂直向、东西向正演结果与观测结果吻合.这也表明采用分解后的地表三维同震形变场可以有效地识别出发震断层的少量左旋走滑特征.

This work used a least square iterative approximation algorithm based on priori knowledge to calculate three-dimensional co-seismic deformation of the Da Qaidam earthquakesfrom ascending,descending and wide-swath data of Envisat ASAR.The results show that the vertical deformation of MW6.3earthquake in 2008 occurred mainly in the south wall of the fault,where uplift is dominant.The maximum displacement is about 10 cm.The subsidence on the north wall of the fault is less than-1cm.The east-west component on the south fault exhibits eastward movement with a maximum of 4cm.The north wall moves westward with-2cm maximum.For the MW5.8earthquake in 2009,the south wall of the fault uplifted with 27 cm maximum value.The maximum subsidence of the north wall is about-3cm.The component of east-west deformation manifests the south wall moves to east,and the maximum amount is about10 cm.The maximum westward movement of the north wall is about-4cm.In short,the sources of Da Qaidam earthquakes in 2008 and 2009are thrust faulting with a small left-lateral strike slip component.It is impossible to judge the little strike-slip of co-seismic deformation with single light of sight,while the sinistral or dextral characteristics of the seismic source could be identified through the three-dimensional deformation of the surface.Besides,we have made forward modeling of the 3Dco-seismic deformation field of the 2008 MW6.3earthquake using the Okada model with the constraints of LOS,vertical and east-west deformation.The simulation results of these displacements are in good agreement with the observations by using a thrust seismogenic fault model with small left-lateral strike slip,which verifies the reliability of computation results and allows to recognize effectively the characteristic of small left-lateral strike slip using decomposition results.