InSAR约束下的2008年汶川地震同震和震后形变分析

2008年5月12日，青藏高原东缘的龙门山断裂带上发生了M_w7.9级汶川地震.本文通过分析覆盖汶川地震震中区域的ALOS/PALSAR像对的方位向偏移量来选择无明显电离层扰动影响的像对进行干涉处理，获取了高精度、连续的InSAR地表形变场.在此基础上，结合高精度GPS同震形变数据，采用同震、黏弹性松弛震后形变联合反演模型同时确定了汶川地震的同震滑动分布和龙门山地区的流变结构参数.研究结果表明，汶川地震是一个断层破裂非常复杂的地震事件，其中，北川段、岳家山段、虹口段和汉旺段的滑动以逆冲为主，而青川段以右旋走滑为主.滑动主要发生在10 km深度以上的区域，最大滑动量位于虹口段的东北端，达10.7 m.地震释放的总能量为9.28×10²⁰ N·m（M_w7.91），与地震学的结果一致.联合反演模型确定的龙门山地区中下地壳的黏性系数为2×10¹⁸ Pa·s，为青藏高原东部地区的黏性系数提供了一个可靠的下限值.如果有更长时间的震后形变观测时间序列，将为该区域提供更为可靠的流变结构.

Coseismic and postseismic deformation of the 2008 Wenchuan Earthquake from InSAR

On 12 May 2008, an M_w7.9 earthquake occurred on the Longmenshan fault system at the eastern margin of the Qinghai-Tibet Plateau near Wenchuan City. Here we obtained the ionospheric perturbations in Japanese ALOS/PALSAR images covering the epicenter of Wenchuan earthquake from the corresponding azimuth offsets, and determined highly precise and continuous InSAR surface displacements using those that are not strongly affected by ionospheric perturbations. Combing with the GPS coseismic deformation, a joint model considering both coseismic and postseismic phases is constructed to study the coseismic slip distribution of the Wenchuan earthquake and the viscous structure of the Longmenshan region. The best-fitting slip model suggests that the earthquake is an event with very complex fault rupture. The slips of Hongkou, Yuejiashan, Beichuan, and Hanwang segments are dominated by the thrust movement and the Qingchuan segment experiences a dominant right-lateral strike slip. The major slip occurred mainly at the depth of less than 10 km, with a maximum slip of 10.7 m on the northeastern Hongkou segment. The determined geodetic moment is approximately 9.28×10²⁰ N·m(M_w7.91), which is consistent with the results of seismology. The mid to lower crustal viscosity derived from the joint model in a Maxwell half-space is 2×10¹⁸ Pa·s, which places a strong low bound on viscosity in the Longmenshan region. Postseismic displacements time series covering a longer time span might have the potential to improve this constraint.