| 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 |
| |
| 引用本文： | 谭凯,王琪,丁开华,李恒,邹蓉,聂兆生,王迪晋,杨少敏,乔学军.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[J].地球物理学报,2015,58(9):3169-3182. |
| |
| 作者姓名： | 谭凯 王琪 丁开华 李恒 邹蓉 聂兆生 王迪晋 杨少敏 乔学军 |
| |
| 作者单位： | 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 |
| |
| 基金项目： | 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.
|
| 关 键 词： | 芦山地震 同震形变 断层几何形状 破裂滑动分布 |
| 收稿时间： | 2015-01-09 |
Rupture models of the 2013 Lushan earthquake constrained by near field displacements and its tectonic implications |
| |
| TAN Kai,WANG Qi,DING Kai-Hua,LI Heng,ZOU Rong,NIE Zhao-Sheng,WANG Di-Jin,YANG Shao-Min,QIAO Xue-Jun.Rupture models of the 2013 Lushan earthquake constrained by near field displacements and its tectonic implications[J].Chinese Journal of Geophysics,2015,58(9):3169-3182. |
| |
| Authors: | TAN Kai WANG Qi DING Kai-Hua LI Heng ZOU Rong NIE Zhao-Sheng WANG Di-Jin YANG Shao-Min QIAO Xue-Jun |
| |
| Institution: | 1. Key Laboratory of Earthquake Geodesy, Institute of Seismology, CEA, Wuhan 430071, China;
2. Institute of Geophysics & Geomatics, China University of Geosciences, Wuhan 430074, China;
3. Faculty of Information Engineering, China University of Geosciences, Wuhan 430074, China |
| |
| Abstract: | Following the 2008 Wenchuan MS8.0 earthquake in the Longmen Shan fault zone, the 2013 Lushan MS7.0 earthquake 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 10~15 km, characterized by a predominating 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 accelerate-meter 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 while maintaining smoothness of slip across the neighboring patches by the cross validation sum of squares.
The updated data set of static offsets includes additional 30 stations, and are double in number the early one. All stations are located largely in a region in dimension of 80~100 km between Qionglai and Tianquan. The maximum offset of 67 mm is found at one GPS station 16 km away from the epicenter. The surface displacements are all directed to the epicenter, in consistent with thrusting mechanism. The uncertainty for the continuously-operating GPS stations is less than 3 mm, and less than 5 mm for the campaign stations whereas the uncertainty of horizontal components of a strong-motion station is estimated to be about 10 mm by comparing with the GPS data. Our modeling indicates that the strike of the rupture is about 212° parallel to the topographic front of the Longmen Shan. Our preferred model plane is approximated by a listric fault with a steeply-dipping ramp shallower than 16 km, which soles into agently-dipping detachment at 16~25 km. The dip angle is greater than 40° for the ramp and is reduced to less than 30° for the detachment fault. Our slip model consists of two main patches with local pick slip exceeding 0.5 m. One are located at the ramp with dip angles of 43°~50°. The maximum slip of 1.5 m is found at 13 km depth. Another is on the detachment faults that dips 27°. The slip on the detachment fault is extended downwards to the depths of 25~26 km where aftershocks ceased. The relocated aftershocks surround largely the main slip patches. The majority of the aftershocks were restricted to the areas that experienced an enhanced Coulomb stress due to the main shock. The geodetic moment is estimated to 1.14×1019N·m corresponding to the moment magnitude Mw6.6 in accordance with the GCMT solution. The seismic imaging of deep structures beneath the Longmen Shan reveals the P-wave velocities change abruptly at the depths of 13~17 km, coincident with the location of the décollement inferred from our model. The magnetotelluric observation shows that the Longmen Shan fault corresponds to as a gently-dipping conductor that extend downward to the depth of about 20 km, coincident with the location of the décollement.
The deep slip caused by the 2013 Lushan earthquake is found along the southern section of the Longmen Shan, and is much consistent with that of central and northern Longmen Shan caused by the 2008 Wenchuan earthquake. The observation provides evidence for the existence of a ramp-décollement preferred by a thin-skined tectonics for the Longmen Shan. The opposite viewpoint is a thick-skinned tectonics that requires a steeper basal fault to uplift the Longmen Shan. Our modelling precludes such a deep fault extending into the mid- and lower crust. The ramp-décollement under the Longmen Shan highlights the crustal shortening across the eastern margin of the Tibetan Plateau to uplift the Longmen Shan. The rigid Sichuan Basin basement underthrusts under the Longmen Shan along the detachment layer. The ramp-décollement adjusts the compressional deformation on the eastern margin of the Tibetan Plateau, resulting in the uplift of the Longmen Shan. |
| |
| Keywords: | Lushan earthquake Coseismic deformation Fault geometry Rupture slip distribution |
| 本文献已被 CNKI 等数据库收录！ |
| 点击此处可从《地球物理学报》浏览原始摘要信息 |
| 点击此处可从《地球物理学报》下载免费的PDF全文 |
|
