近场位移数据约束的2013年芦山地震破裂模型及其构造意义  

Rupture models of the 2013 Lushan earthquake constrained by near field displacements and its tectonic implications

作　　者：谭凯[1] 王琪[2] 丁开华 李恒[1] 邹蓉[2] 聂兆生[1] 王迪晋[1] 杨少敏[1] 乔学军[1] 

机构地区：[1]中国地震局地震研究所地震大地测量重点实验室,武汉430071 [2]中国地质大学(武汉)地球物理与空间信息学院行星科学研究所,武汉430074 [3]中国地质大学(武汉)信息工程学院,武汉430074

出　　处：《地球物理学报》2015年第9期3169-3182,共14页Chinese Journal of Geophysics

基　　金：中国地震局地震研究所所长基金(IS201506220);国家自然科学基金(40974012;41304019);地震行业科研专项(201208006)资助

摘　　要：以往的研究显示了2013年芦山MS7.0级地震发震断层的隐伏逆冲断层基本特征,但是破裂深部细节差异较大.本文以近场密集的同震形变数据约束芦山地震破裂面几何形状及滑动分布,结果显示芦山地震破裂面具有铲状结构,上部16km为43°～50°高角度断层,深部16～25km为小于27°的低角度断层,破裂深度与重定位的余震分布深度一致.破裂分布模型清楚显示上下两个断层上各有一个滑动幅度大于0.5m的峰值破裂区,最大滑动量1.5m位于13km深处.重定位的余震分布基本都落在最大滑动量等值线外部库仑应力增加的区域.芦山地震破裂面几何形状和滑动分布特征与2008年汶川MS8.0级地震映秀—北川破裂相似,支持龙门山冲断带发育大规模的近水平滑脱层,是青藏高原东缘地壳缩短增厚、龙门山挤压隆升的重要证据。Following the 2008 Wenchuan MS8.0earthquake in the Longmen Shan fault zone,the2013 Lushan MS7.0earthquake struck its southwestern section.Analysis of seismic waves and coseismic surface displacements together with field investigations all show that this earthquake ruptured a compact areas at depths of 10～15km,characterized by apredominating thrust motion that may not reach to the surface.Yet the results differ considerably in details about the geometry and distribution of coseismic slip,partly owing to the scarcity of near-field observation,it remains elusive whether the coseismic slip has extended downward in a fashion similar to what the Wenchuan earthquake did along a deep-seated décollement under the Longmen Shan.We used an improved data set of near-field coseismic deformation acquired by GPS receivers and acceleratemeter to constraint the rupture geometry and slip distribution.We show the existent of coseismic slip on a basal detachment fault,which suggests that the Longmen Shan is thickened at this part by crustal shortening between the Tibetan Plateau and the Sichuan Basin.We combined near field coseismic offsets acquired by continuously-operating and campaign GPS stations as well as seismic strong motion stations.We processed GPS data with GIPSY software,and integrate twice acceleration waveforms with zero correction method to obtain static offsets caused by the earthquake.We use these data to constrain the rupture geometry and slip distribution based on the half-space elastic dislocation model.Firstly,we used the simulated annealing algorithm to determine model parameters and corresponding confidence intervals assuming that coseismic slip is distributed on multiple rectangle planes.Then,we divide the optimal model planes further into numerous sub-fault patches,and use the nonnegative least squares to estimate slip values on these patches to outline collectively feature of the distribution of coseismic slip on this optimal rupture plane.In both inversions,we minimize misfits to surface displacements wh

关 键 词：芦山地震 同震形变 断层几何形状 破裂滑动分布 

分 类 号：P228[天文地球—大地测量学与测量工程] P313[天文地球—测绘科学与技术]