汶川M_W 7.9和集集M_W 7.6地震前应力场转换现象及其可能的前兆意义  

The precursory significance of tectonic stress field transformation before the Wenchuan M_w7.9 Earthquake and the Chi-Chi M_w7.6 Earthquake

作　　者：刁桂苓[1] 徐锡伟[2] 陈于高[3] 黄柏寿 王晓山[1] 冯向东[1] 杨雅琼[1] 

机构地区：[1]河北省地震局,石家庄050021 [2]中国地震局地质研究所,北京100029 [3]台湾大学地质系,台北10617 [4]中研院地球科学研究所

出　　处：《地球物理学报》2011年第1期128-136,共9页Chinese Journal of Geophysics

基　　金：国家自然科学基金课题(40821160550);科学技术部国际合作项目(2009DFA21280)资助

摘　　要：2008年四川汶川M_W 7.9地震和1999年台湾集集M_W7.6地震均为挤压推覆构造环境下发生的板内逆断层型地震.通过对比分析2次地震前的CMT解、震源区附近的中小地震震源机制解及其反演的应力场可知,集集地震主震震源机制解与用台湾内陆中西部的CMT解反演得到的逆断层类型构造应力场吻合,而在主震前震源区附近中小地震震源机制解反演得到与构造应力场不一致的走滑类型局部应力场,但当局部应力场变化到与构造应力场一致时,数月后发生主震;同样,用青藏高原东部的CMT解震源机制反演得到走滑类型的构造应力场,逆断层类型的汶川主震与构造应力场的压应力轴吻合,震区附近中小地震反演得到了与构造应力场一致的区域应力场,但震前局部应力场变化与逆断层类型应力场一致时,随即发生主震.说明逆断层型主震区附近随着震源区应力积累,在震前会出现相似的局部应力场转换现象,当最终转换到与发生主震的应力状态一致时,表明震源区附近应力已达到相当高的应力水平,可能是发生大地震的征兆,应引起进一步的关注.The 2008 Wenchuan earthquake and the 1999 Chi-Chi earthquake are both intraplate thrust fault earthquakes occurred under the tectonic setting of thrust-nappe. Through comparative analysis on CMT solutions, focal mechanism solutions of small and moderate earthquakes, and tectonic stress field near the mainshock region, we found that the thrust type focal mechanism of the Chi-Chi mainshock coincides with the tectonic stress field derived from the CMT solutions of earthquakes occurred in Taiwan central and western inland; but the small and moderate earthquakes randomly occurred near mainshock region resulted in strike slip type focal mechanisms, indicating the local stress field is not consistent with the tectonic stress field before the Chi-chi mainshock; the Chi-chi mainshcok occurred after a few months when the local stress field is consistent with the tectonic stress field. Similarly, the compressive stress axis of the thrust fault type focal mechanism of Wenchuan mainshock coincides with the compressive stress axis of tectonic stress field inverted from the CMT solutions of earthquake occurred in the eastern part of Qinghai-Tibet Plateau, the local stress field inverted from the focal mechanisms of small and moderate earthquakes near Wenchuan mainshock is consistent with the tectonic stress field. When the local stress field is consistent with the thrust fault type stress field, the Wenchuan mainshock occurred immediately. With the stress accumulation near the source region, there are similar local stress field transformation phenomena before the thrust fault mainshock. When the local stress state transformed to the stress state of mainshock, the stress level is very high near the source region. It may be precursor of large earthquake and must arouse further concerns.

关 键 词：汶川地震 集集地震 构造应力场 局部应力场 应力场转换 强震发生的征兆 

分 类 号：P553[天文地球—构造地质学]