【摘要】 本文首先阐明汶川M_S8.0级地震发生在由区域布格重力异常和地震震中分布所确定的武都——松潘—茂汶—汶川—沪定地震带上.汶川地震所在地段是地震前兆和中小地震(M≤7.0)的空白区,震前出现明显的孕震空区,M_S8.0级地震发生在空区周围区域中小地震活动峰值之后的减少段里.地震的破裂超出孕震空区范围,空区内、外余震活动呈现出不同的衰减特征,依此将余震活动分为WS和NE两个区段.地震破裂过程、4级以上余震矩张量及震区应力场反演和余震应力降的测定结果表明.两个区域的位错、余震机制解和应力降及最大主应力的方向等明显有别.根据这些特征和地震应力触发的研究,推测NE段地震的发生可能是由WS段主破裂的发生所触发.更多还原

【Abstract】 In this paper, we firstly demonstrated that the M_S 8. 0 earthquake occurred on the Wudu-Songpan-Maowen-Wenchuan-Luding seismic zone,which is delineated by the regional gravity anomalies and seismic activity. The main ruptured region of the earthquake was located on a segment that lacked strong earthquakes during the active seismic period, i. e. seismic gap. The seismic gap is very remarkable before the M_S 8. 0 event and the main event occurred in the period of decreased seismicity outside the gap area. The rupture process extended towards NE direction and exceeded the seismic gap region. Seismicity in and out the gap show different active features, therefore the aftershock seismicity is divided into NE and WS segments by the author. Researches on source rupture process, moment tensor inversion of M≥4.0 aftershocks, stress field inversion, as well as the stress drops of aftershocks reveal that there exists significant difference between the two segments in slip distribution on the fault, focal mechanisms of aftershocks, stress drops, as well as direction of the tress field. According to those characteristics and study on the stress triggering, it is suggested that the seismicity on the NE segment may be triggered by the main rupture starting on WS segment.更多还原