李平恩^1,2,,
廖力^1,2,
奉建州^1,2
1. 中国地震局地球物理研究所, 北京 100081
2. 北京白家疃国家地球科学野外科学观测研究站, 北京 100095

基金项目: 国家自然科学基金项目(41674105), 中国地震局地球物理研究所基本科研业务费专项(DQJB19B27, DQJB19A0123, DQJB21X25, DQJB20X09)共同资助


详细信息

作者简介: 李平恩, 男, 1977年生, 副研究员, 主要从事地球动力学数值模拟方面的研究.E-mail: pingen2000@163.com

中图分类号: P315

收稿日期:2021-07-22
修回日期:2021-09-13
上线日期:2021-10-10

Numerical simulation study of instability mechanism of the 2008 Wenchuan earthquake

LI PingEn^1,2,,
LIAO Li^1,2,
FENG JianZhou^1,2
1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
2. Beijing Baijiatuan Earth Sciences National Observation and Research Station, Beijing 100095, China


MSC: P315

--> Received Date: 22 July 2021
Revised Date: 13 September 2021
Available Online: 10 October 2021


摘要
摘要:考虑断层的软化特性，建立垂直于龙门山断裂带并包含四川盆地和川西高原在内的汶川地震不稳定性地震力学模型.采用有限元方法计算得到了描述整个岩石力学系统稳定性状态和过程的平衡路径曲线.在此基础上，采用稳定性理论研究了汶川地震从孕育到发生的过程，讨论了断层倾角和断层材料参数对地震失稳的影响.数值模拟结果显示，系统只存在稳定的断层无震滑动和不稳定的地震失稳2种状态.断层倾角、初始内摩擦系数、初始黏聚力和强度曲线形状参数的增加会导致系统趋向不稳定的地震失稳状态.而强度曲线胖度参数的增加有助于系统进入稳定的断层缓慢无震滑动状态.地震失稳前，在平衡路径曲线的应力峰值点和失稳点之间，断层错动加速，应变能开始释放并且应力开始减小，是失稳的前兆.最后在失稳点发生应力突跳，地震发生，其间伴随应变能的急剧释放、应力降和断层突然错动.无论是稳定的断层无震滑动还是不稳定的地震失稳，系统重新进入应力和应变能增加状态后，应力和应变能的增速由远场加载速度、岩石力学系统的结构和围岩材料属性决定，与断层软化特性参数无关.
关键词: 汶川地震/
失稳机制/
断层软化特性/
平衡路径曲线/
有限元

Abstract:Considering the softening characteristics of faults, a plane earthquake mechanics model of the Wenchuan earthquake instability is established, which perpendicular to the Longmenshan fault zone and includes the Sichuan Basin and the Western Sichuan Plateau. The equilibrium path curve describing the stability state and process of the whole rock mechanics system is obtained by using the finite element method. Then the process of the Wenchuan earthquake from preparation to occurrence is studied by using stability theory, and the influence of fault dip and fault material parameters on earthquake instability is discussed. The results show that the system has only two states: stable fault aseismic sliding and unstable earthquake instability. The increase of fault dip, initial internal friction coefficient, initial cohesion and shape parameters of the strength curve will lead to the instability of the system. The increase of the fatness parameter of the strength curve is helpful for the system to enter a stable state of slow and aseismic sliding of faults. Before an earthquake instability, between the peak stress point and the instability point of the equilibrium path curve, the fault dislocation accelerates, the strain energy begins to release and the stress begins to decrease, which is the precursor of the instability. Finally, a sudden stress jump occurs at the instability point and an earthquake occurs, with the rapid release of strain energy, stress drop and sudden fault dislocation. Whether it is stable fault aseismic sliding or unstable earthquake instability, after the system re-enters the state of stress and strain energy increasing, the growth rate of stress and strain energy is determined by far field loading rate, the structure of rock mechanics system and the properties of surrounding rock material, and is independent of the fault softening characteristic parameters.
Key words:Wenchuan earthquake/
Instability mechanism/
Softening characteristics of faults/
Equilibrium path curve/
Finite element method



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