| 断层横向构造在逆冲型地震破裂中的作用——以汶川地震小鱼洞断层为例 |
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| 引用本文： | 王鹏,刘静.断层横向构造在逆冲型地震破裂中的作用——以汶川地震小鱼洞断层为例[J].地球物理学报,2014,57(10):3296-3307. |
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| 作者姓名： | 王鹏 刘静 |
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| 作者单位： | 中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029 |
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| 基金项目： | 中国地震局地震行业专项(201308012),国家杰出青年科学基金(41225010)资助. |
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| 摘 要： | 大地震破裂大多由横向构造(如阶区、弯曲和分叉)所分割的多个段落组成.2008年5·12汶川地震破裂沿北东走向上穿过了多个横向构造部位,特别在震中北东45 km的位置,小鱼洞断层、北川断层和彭灌断层三者之间呈现复杂的断裂切割相交关系.复杂断层几何结构对破裂的扩展是有抑制还是促进的作用？在相交的断裂段之间是否存在最优的破裂顺序？本文以库仑应力分析为手段,探讨在汶川同震破裂初始30 s内,破裂在多分支断裂中选择扩展路径时的可能应力相互作用.库仑应力分析显示:如果北川断层先发生破裂,其滑动对小鱼洞断层和彭灌断层均产生强烈负应力的抑制作用,而彭灌断层的滑动却反而对小鱼洞断层和北川断层浅部有强烈正应力的促进作用.因此,从准静态应力分析角度,彭灌断层先于北川断层发生破裂的可能性较大,这一破裂顺序与小鱼洞断层参与同震破裂过程的事实相符.此外,小鱼洞断层在链接北川和彭灌断层的同震位移中可能起到桥梁作用,但非静态应力的影响.横向构造在逆冲型地震破裂扩展过程中起到的牵引作用使得逆冲型地震破裂能够比走滑型地震跨越更宽的阶区.横向构造是逆冲断裂带内广泛发育的构成单元,因此在地震危险性分析的最大潜在震级测算中应该考虑其作用.
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| 关 键 词： | 汶川地震 小鱼洞断层 横向构造 库仑应力分析 |
| 收稿时间： | 2014-02-12 |
The role of the transverse structure in reverse-type earthquake rupture propagation: A case study on the Xiaoyudong fault in the Wenchuan earthquake |
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| WANG Peng,LIU-ZENG Jing.The role of the transverse structure in reverse-type earthquake rupture propagation: A case study on the Xiaoyudong fault in the Wenchuan earthquake[J].Chinese Journal of Geophysics,2014,57(10):3296-3307. |
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| Authors: | WANG Peng LIU-ZENG Jing |
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| Institution: | State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China |
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| Abstract: | Coseismic rupture of large earthquakes commonly consists of multiple fault segments separated by transverse structures, such as step-overs, bends, splays of varying sizes. These complexities have been long considered playing important roles in controlling the initiation, evolution and termination of ruptures and thus the final sizes of earthquakes. The 2008 Wenchuan earthquake rupture, also consisting of multiple fault segments, is the result of breaching through a series of significant transverse structures. Especially at the location of ~45 km northeast of the epicenter, the Xiaoyudong fault intersects the Beichuan and Pengguan faults, forming complex fault geometry. Does the geometrical complexity retard or promote rupture propagation? Is there an optimized path or sequence of rupture cascading through? In this paper, we explore the possible stress state for the 30s initial stage of development when rupture passed through multi-branch faults and stress interaction among faults near the Xiaoyudong during the Wenchuan earthquake. Coulomb stress analysis indicates that if the Beichuan fault failed first, it would cast a strong negative stress shadow on both Pengguan and Xiaoyudong faults; on the other hand, slip on the Pengguan fault would exert a strong positive Coulomb stress on the Beichuan and Xiaoyudong faults. Thus, quasi-static stress favors failure on the Pengguan fault prior to that on the Beichuan fault. This is also compatible with the fact that the Xiaoyudong fault failed coseimsically. The static stress exerted by the coseismic slip on the Xiaoyudong fault is small, and secondary to its bridging role in fast transmission of dynamic stress in front of rupture front. The transverse structure tends to play a positive role in linking coseismic slip transfer between parallel thrusts, rather than inhibiting them, so that rupture can jump step-overs wider than in a strike-slip setting. As transverse structures are common features in reverse fault systems, we should consider their bridging roles when calculating the maximum potential earthquake magnitude in seismic hazard evaluation. |
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| Keywords: | Wenchuan earthquake Xiaoyudong fault Transverse structure Coulomb stress analysis |
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