THREE-DIMENSIONAL DEFORMATION OF THE 2008 GAIZE EARTHQUAKES RESOLVED FROM INSAR MEASUREMENTS BY MULTIPLE VIEW ANGLES AND ITS TECTONIC IMPLICATIONS

doi:10.3969/j.issn.0253-4967.2016.04.014

Abstract

Abstract:

The 2008 Gaize M_W6.4 earthquake,occurring on the tensional active fault zone located between Lhasa terrane and Qiangtang terrane in the interior of Tibet is a typical normal-faulting event.In this paper,we resolve the three-dimensional coseismic displacement fields of the earthquakes using a least-square iterative approximation solution with a priori knowledge,according to the theoretical basis that InSAR measurements are extremely insensitive to N-S component.Results show that the boundary dividing the two sides of the main-shock fault is very clear in the vertical movement,and two remarkable subsidence centers can be observed on the hanging wall,while amplitude of the west one (-48.9cm) is larger than the east (-41.4cm),but the maximum uplift on the footwall is only 5cm.In addition to some northward movement with amplitude less than 5cm around the aftershock fault,the north-south deformation field suggests an overall southward movement.The three-dimensional results indicate that the induced surface movement is predominantly vertical and mostly occurred on the upper side,while there are obvious east-west separation and eastward rotation in the horizontal plane.The full vectors are consistent with simulated deformation field with the RMSE less than 6cm,so the research demonstrates the feasibility of the method to recover precise three-dimensional deformation field.On the whole,the three-dimensional deformation field coincides with the tensile fracture characteristics of Gaize earthquakes,and the tectonic stress background of coeval east-west extension and north-south shortening.

Key words: the 2008 Gaize earthquake, InSAR, multiple view angles, three-dimensional deformation field

摘要：

2008年西藏改则M_W6.4地震发生于青藏高原腹地拉萨块体与羌塘块体之间的张性活动构造带上，是一次典型的正断层破裂事件。基于InSAR对SN向形变的极度不敏感性，文中利用结合先验条件的最小二乘迭代逼近法解算了改则地震的三维同震形变场。结果显示：主震断层两盘的垂直运动差异明显，上盘存在明显的沉降“双心”特征，量值分别为-41.4 cm、-48.9cm，而下盘的最大隆升量仅5cm；除余震断层附近存在小量级（<5cm）的N向形变外，SN向形变总体趋势向S；三维形变场的整体以垂直形变为主，并集中于上盘，而水平形变具有明显的EW向分离和E向旋转特征；所得到的各形变分量与模拟值的残差标准差不超过6cm，说明此方法能够用于获取精度较高的三维同震形变场。整体上，三维形变场的分解结果与改则地震的张性破裂特征及其所处的EW向拉伸、SN向压缩构造应力背景呈现一致性特征。

关键词: 2008年改则地震, InSAR, 多视角, 三维形变场

CLC Number:

P315.2

WANG Jia-qing, ZHANG Guo-hong, SHAN Xin-jian, ZHANG Ying-feng. THREE-DIMENSIONAL DEFORMATION OF THE 2008 GAIZE EARTHQUAKES RESOLVED FROM INSAR MEASUREMENTS BY MULTIPLE VIEW ANGLES AND ITS TECTONIC IMPLICATIONS[J]. SEISMOLOGY AND GEOLOGY, 2016, 38(4): 978-986.

王家庆, 张国宏, 单新建, 张迎峰. 2008年西藏改则地震多视角InSAR成果的三维形变解算及初步分析[J]. 地震地质, 2016, 38(4): 978-986.

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