CHARACTERS OF SURFACE DISPLACEMENT DUE TO BLIND CURVED FAULT REVEALED BY NUMERICAL MODELS

doi:10.3969/j.issn.0253-4967.2013.02.022

Abstract

Abstract:

A possible three-dimensionally highly-curved fault,suspected as the ruptured structure of the Lushan M7.0 earthquake,is revealed by relocated aftershocks. A recent study shows that obvious differences exist between curved fault and straight fault under the ground in regard to dislocation patterns and co-seismic stress responses on the planes ruptured during an earthquake. Infinite half-space dislocation models reveal that the characters of surface displacements due to a curved fault are similar to that from straight reverse fault as a whole. Nevertheless,the horizontal displacements due to slip on a curved fault show closer trend parallel to the direction of regional shortening and higher magnitude than that from a straight fault. Subsequently,the curved fault is suggested to be more capable of transferring horizontal movement of hanging-wall materials in large area. Relative to the case on a straight fault,horizontal displacement in foot-wall area of a curved fault decays more with distance from source fault. On the other hand,the curved fault generates obviously less co-seismic uplift while larger and more extensive surface drop somewhere than the reverse fault or left-lateral reverse fault of the same size but with straight fault planes does. For relatively small magnitude of main shock,it is not easy to determine whether the structure of rupture during Lushan earthquake is highly-curved fault or not due to the sparse observations on co-seismic deformation like GPS.Dense and high-resolution observations should be required to survey the features of focal structure in detail.

Key words: Lushan M7.0 earthquake, curved fault, blind fault, reverse fault, surface displacement

摘要：

余震精定位资料显示,芦山7.0级地震破裂面可能为弯曲程度较高的三维弯曲断层.相关研究显示,这种弯曲断层的位错方式和破裂面同震应力加卸载模式与普通平直断层有明显不同.文中采用无限半空间位错模型模拟显示,隐伏弯曲断层和平直逆断层引起的地表位移特征相似,但是弯曲断层引起的地表水平位移更接近区域整体的地壳缩短方向,缩短方向水平位移的量明显高于同等规模的平直逆断层,因此能更好地传递断层上盘大范围物质的水平运动.相对于平直断层,弯曲断层下盘水平位移随距离衰减十分明显.同等规模的弯曲断层导致的同震地表抬升小于平直逆断层或左旋逆断层引起的同震抬升,但能造成更明显的地表下降.由于地震规模较小,GPS等低密度空间分布的形变观测可能无法有效分辨芦山地震震源结构是否为弯曲断层.对震源结构的细节研究,还有待于利用高空间密度和高分辨率的形变观测资料.

关键词: 芦山7.0级地震, 弯曲断层, 隐伏断层, 逆断层, 地表位移

CLC Number:

P315.2

ZHANG Zhu-qi, CHEN Tao, REN Zhi-kun, WANG Wei-tao. CHARACTERS OF SURFACE DISPLACEMENT DUE TO BLIND CURVED FAULT REVEALED BY NUMERICAL MODELS[J]. SEISMOLOGY AND GEOLOGY, 2013, 35(2): 452-460.

张竹琪, 陈涛, 任治坤, 王伟涛. 数值模型显示的隐伏弯曲断层同震地表位移特征[J]. 地震地质, 2013, 35(2): 452-460.

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