SEISMOLOGY AND GEOLOGY ›› 2018, Vol. 40 ›› Issue (1): 12-26.DOI: 10.3969/j.issn.0253-4967.2018.01.002

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ZHAO You-jia, ZHANG Guo-hong, ZHANG Ying-feng, SHAN Xin-jian, QU Chun-yan   

  1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China
  • Received:2017-11-08 Revised:2018-01-03 Online:2018-02-20 Published:2018-04-13


赵由佳, 张国宏, 张迎峰, 单新建, 屈春燕   

  1. 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
  • 通讯作者: 张国宏,副研究员,
  • 作者简介:赵由佳,女,1993年生,固体地球物理学专业在读硕士研究生,主要研究方向为震源动力学,电话:010-62009024,。
  • 基金资助:

Abstract: The May 12, 2008 MS7.9 Wenchuan earthquake is ranked as one of the most devastating natural disasters ever occurred in modern Chinese history. The Longmenshan Fault(LMSF) zone is the seismogenic source structure, which consists of three sub-parallel faults, i.e., the Guanxian-Jiangyou Fault(GJF) in the frontal, the Yingxiu-Beichuan Fault(YBF) in the central fault and the Wenchuan-Maowen Fault(WMF) in the back of the LMSF. In this study, geological survey and seismic profiles are used to constrain the faults geometry and medium parameters. Three visco-elastic finite element models of the LMSF with different main faults are established. From the phase of interseismic stress accumulation to coseismic stress release and postseismic adjustment, the Wenchuan earthquake is simulated using Continuous-Discrete Element Method(CDEM). Modeling results show that before the 2008 Wenchuan earthquake, the GJF becomes unstable due to the interaction between its unique fault geometry and the tectonic stress loading. In the fault geometry model, the GJF is the most gently dipped fault among the three faults, which in return makes it having the smallest normal stress and the greatest shear stress. The continuous shear stress loading finally meets the fault failure criteria and the Wenchuan earthquake starts to initiate on the GJF at the depth of 15~20km. The earthquake rupture then propagated to the YBF. At the same time, due to the GJF and YBF rupture, the interseismic stress accumulation has been greatly reduced, causing the WMF failed to rupture. Although the stress accumulation in the WMF has been reduced significantly after the earthquake, yet it has not been released completely, which means that the WMF likely has with high seismic risk after the 2008 Wenchuan earthquake. We also find that the stress perturbation caused by gently dipping segment of the fault can promote the passive rupture in the steeply dipping segment, making the upper limit of dip angles larger than traditional assumption.

Key words: continuous-discrete element method, Wenchuan earthquake, spontaneous rupture, complete period simulation, multi-fault interaction

摘要: 首先利用地震地质调查、地震剖面探测结果对汶川地震的发震断层几何形态及周边块体介质参数进行约束,建立了3个包含有不同主断层的龙门山断裂带二维黏弹性有限元模型;然后基于连续-离散单元法对汶川地震的孕育与发生进行了全周期模拟,包括震间应力积累阶段、同震应力释放阶段及震后恢复调整阶段。模型对比研究结果表明,龙门山断裂带中由于断层几何结构及断层面剪切应力与正应力的综合作用,使得最先达到断层破裂准则阈值的灌县-江油断层率先破裂,初始破裂在深度15~20km处,破裂进一步传导至映秀-北川断层;同时由于灌县-江油断层与映秀-北川断层的破裂导致系统内应力大幅度降低,使得灌县-江油断层不具备产生同震破裂的应力条件。然而,尽管汶川-茂汶断层上的应力水平与汶川地震前相比有所减弱,但仍积累了较高的震间应力,可能预示其在汶川地震后具有较高的地震危险性。模拟结果还表明,铲型逆冲断层系统的深部断层破裂能够推动浅部高倾角区域发生被动破裂,因而其发震断层的倾角上限很可能比传统认识的大。

关键词: 连续-离散单元法, 汶川地震, 自发破裂, 全周期模拟, 多断层相互作用

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