SEISMOLOGY AND GEOLOGY ›› 2014, Vol. 36 ›› Issue (3): 547-561.DOI: 10.3969/j.issn.0253-4967.2014.03.001

• CONTENTS • Previous Articles     Next Articles

ACCELERATED SYNERGISM PRIOR TO FAULT INSTABILITY：EVIDENCE FROM LABORATORY EXPERIMENTS AND AN EARTHQUAKE CASE

MA Jin, GUO Yan-shuang   

  1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China
  • Received:2014-02-23 Revised:2014-04-20 Online:2014-09-30 Published:2014-09-30

失稳前断层加速协同化的实验室证据和地震实例

马瑾, 郭彦双   

  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
  • 作者简介:马瑾|女|1934年生|研究员|中国科学院院士|现主要研究方向为与地震成因机理有关的构造物理研究|电话：010-62009122|E-mail：majin@ ies.ac.cn。
  • 基金资助:

    国家自然科学基金（41172180，41211120180）和中国地震局地质研究所基本科研业务专项（IGCEA1203）共同资助

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Abstract:

Identification of short-term and impending precursors, including the signal indicating earthquakes are inevitable, is one of focused issues in research of earthquake prediction. To explore this problem, modeling study of instability on a planar strike-slip fault was performed in the laboratory. It is based on the condition that the stress variation curves at a loading machine can reveal the stress state of the specimen and allow us to recognize its meta-instability stage. In terms of the advantage that the information from the loading machine can be compared with observations to the physical quantity of the sample, this work captures and analyzes the differences of temporal-spatial evolution processes of strain parallel and perpendicular to the fault in the stress linearity-off stage and meta-instability stage. The study suggests that a fault consists of relatively fragile and tough portions; the former usually are weakened first as expressed by pre-slip of the fault, and slow or small earthquakes indicative of beginning of strain release; while the latter become the locality of strain accumulation and fast instability finally, i.e. the future seismic source. The synergism process of a fault is actually a process of interaction between different portions of the fault. It is also a conversion from independent activities of each fault segment to synergism activity. The degree of synergism is an indicator of the stress state. It is based on the assumption that an earthquake results from sudden fast slip on a fault which relies on two primary conditions: one is the fault has a high synergism degree which facilitates connection between fault segments resulting in rapid slip of longer fault segments, and the other is sufficient strain is accumulated at some portions of the fault to overcome resistance of local tough portions on the fault. Usually the synergism process of a fault includes three stages: generation of strain-release patches, expansion and increasing of these patches, and mutual connection of strain-release areas. The first stage occurs when the stress curve deviates from linearity, strain variations of different portions of the fault begin to diverge, resulting in isolated patches of strain release and strain accumulation along the fault. In the second stage, related with the quasi-static instability of early meta-instability, those isolated areas of strain release increase and extend steadily. The third stage is equivalent to the late meta-instability that is a quasi-dynamic instability process when the sections of strain release on the fault accelerate to expand and strain levels of strain-accumulation areas accelerate to rise. The accelerated synergism begins at the time when the quasi-static state transforms into the quasi-dynamic state, of which the expansion mechanism of strain release segments changes, i.e. the expansion of isolated fault segments is replaced by connection between fault segments under interaction. At this time the fault is in a critical state and bound to generate earthquakes sooner or later. As a case study, based on the experimental results above and coupled with temporal-spatial evolution of earthquakes on the Laohushan-Maomaoshan Fault west of the Haiyuan Fault zone, this work analyzes the synergism process of the fault before the M6.2 earthquake on 6 June 2000 in this region.

Key words: meta-instability stress state, accelerated synergism process, information of inevitable earthquake, short-term and impending precursor

摘要：

地震是断层的快速错动，它有2个主要条件：一是断层协同化程度较高，一旦应力条件达到，能够迅速连接造成较长断层段的快速错动；二是断层上一些部位积累了足够高的应变，能够克服局部高强部位的错动阻力。地震短临前兆和必震信息识别是地震预报研究的焦点问题之一，为此开展了实验室平直断层失稳模拟研究。从应力变化曲线上可以判定标本所处的应力状态和识别亚失稳应力阶段。利用在实验室便于对压机信息和场上物理量的观测信息进行对比的优势，捕捉和比较应力偏离线性阶段和亚失稳阶段平行断层应变的时空演化过程中的差别。研究表明，由于断层上不同部位相互作用，断层各部位由独立活动逐渐转变为协同化活动，而断层活动协同化程度是判定断层所处应力状态的一个标志。断层活动协同化过程一般包括应变释放点产生、释放点的扩展和增多以及释放段之间相互连接3个阶段：第1阶段发生在偏离线性阶段，断层上不同部位的应变变化开始分化，出现孤立的应变释放区和积累区；第2阶段应变释放区的平稳扩展与亚失稳前期准静态失稳有关，断层上孤立应变释放区增多，并出现稳态扩展；第3阶段相当于亚失稳的后期，即准动态失稳阶段，断层上的应变释放区加速扩展，积累区应变水平加速提高。加速协同化开始于由准静态扩展向准动态扩展的转化，加速的机制是断层段间出现强相互作用。转化的本质在于扩展机制发生了变化，即由孤立断层段的扩展转变为断层段间在相互作用下的连接，这时断层进入发生地震的临界状态。根据实验结果，结合海原断裂带西侧的老虎山-毛毛山断裂地震活动的时空演化，分析了2000年6月6日ML6.2地震前该断层的协同化过程。

关键词: 亚失稳应力状态, 加速协同化, 必震信息, 短临前兆

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