汶川Mw7.9和集集Mw7.6地震前应力场转换现象及其可能的前兆意义

2008年四川汶川Mw7.9地震和1999年台湾集集Mw7.6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...

The precursory significance of tectonic stress field transformation before the Wenchuan Mw7.9 Earthquake and the Chi-Chi Mw7.6 Earthquake

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.