Which Fault Segments Ruptured in the 2008 Wenchuan Earthquake and Which Did Not? New Evidence from Near‐Fault 3D Surface Displacements Derived from SAR Image Offsets
Which Fault Segments Ruptured in the 2008 Wenchuan Earthquake and Which Did Not? New Evidence from Near‐Fault 3D Surface Displacements Derived from SAR Image Offsets
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DOI：
10.1785/0120160126
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发表时间：
2017-06
影响因子：
3
通讯作者：
G. Feng;S. Jónsson;Y. Klinger
中科院分区：
文献类型：
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作者：
G. Feng;S. Jónsson;Y. Klinger
2008年汶川7.9级地震破裂了青藏高原东缘、四川盆地西部复杂的逆冲-断裂系统。尽管对这场地震进行了广泛的研究，但有关地震的几个细节，如地震中哪些断层段被激活，仍不清楚。部分原因是难以实地进入断裂带，部分原因是干涉合成孔径雷达(干涉合成孔径雷达)观测中的近断层观测因去相关性而受到限制。在这项研究中，我们通过估计SAR图像的偏移量来解决这个问题，这些偏移量提供了近断层的地面位移信息，并显示出明显的跨活动断层段的位移不连续。我们从重新分析地震的同震InSAR观测开始，然后通过使用额外的事件后图像，基本上消除了困扰先前研究的强烈电离层信号。我们还估计了SAR图像的偏移量，并利用它们的结果来反演完整的3D同震地表位移场。将InSAR和图像偏移距测量得到的同震形变与全球定位系统和现场观测结果进行了比较。结果表明，我们的观测结果比以前受电离层干扰影响的InSAR研究提供了更好的信息。利用这些结果描述了北川断裂从西南到东北的地表断层错动的细节，发现北川断裂南部(映秀县)存在明显的右旋走滑分量(以及逆冲断层)，这在以前的研究中被严重低估了。根据这一结果，我们提供了新的证据，表明青川断裂在2008年汶川地震中并没有破裂，而是在主震期间或之后立即在北川断裂向北延伸的地方发生了地表断裂。[电子增刊：][1]平行上升轨道同震变形。[1]：http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120160126/-/DC1
The 2008 M w 7.9 Wenchuan earthquake ruptured a complex thrust‐faulting system at the eastern edge of the Tibetan plateau and west of Sichuan basin. Though the earthquake has been extensively studied, several details about the earthquake, such as which fault segments were activated in the earthquake, are still not clear. This is in part due to difficult field access to the fault zone and in part due to limited near‐fault observations in Interferometric Synthetic Aperture Radar (InSAR) observations because of decorrelation. In this study, we address this problem by estimating SAR image offsets that provide near‐fault ground displacement information and exhibit clear displacement discontinuities across activated fault segments. We begin by reanalyzing the coseismic InSAR observations of the earthquake and then mostly eliminate the strong ionospheric signals that were plaguing previous studies by using additional postevent images. We also estimate the SAR image offsets and use their results to retrieve the full 3D coseismic surface displacement field. The coseismic deformation from the InSAR and image‐offset measurements are compared with both Global Positioning System and field observations. The results indicate that our observations provide significantly better information than previous InSAR studies that were affected by ionospheric disturbances. We use the results to present details of the surface‐faulting offsets along the Beichuan fault from the southwest to the northeast and find that there is an obvious right‐lateral strike‐slip component (as well as thrust faulting) along the southern Beichuan fault (in Yingxiu County), which was strongly underestimated in earlier studies. Based on the results, we provide new evidence to show that the Qingchuan fault was not ruptured in the 2008 Wenchuan earthquake, a topic debated in field observation studies, but show instead that surface faulting occurred on a northward extension of the Beichuan fault during or immediately following the mainshock. [Electronic Supplement:][1] Parallel ascending‐orbit track coseismic deformation. [1]: http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120160126/-/DC1