【摘要】 2015年4月25日尼泊尔发生M w7.8级大地震,震源机制解结果一致表明该地震为低角度逆冲型.迄今发生百余次余震,其中包括M s7.0级以上强余震,并触发正断层型小震群.此次地震发生于喜马拉雅碰撞造山带中段,位于1934年比哈-尼泊尔M w~8.1级和1505年木斯塘M w~8.2级地震之间的地震空区内,是自1950年察隅M w~8.4级地震以来喜马拉雅主逆冲断裂上发生的最大震级地震.为更好地理解这次地震,本文综述喜马拉雅造山带的构造背景、断裂组合构成和几何形态、历史强震分布和破裂范围、现代小地震活动性特征、强震孕育的基本模式、震间加载和同震位移的空间互补性.在简单介绍同震破裂的断面初始解基本特征基础上,初步讨论了这次尼泊尔地震与喜马拉雅带特征型地震的关系,与2008年汶川地震的比较,以及低角度逆冲地震破裂的地表出露和对区域地震危险趋势的指示意义等问题.更多还原

【Abstract】 An earthquake of M w 7.8 occurred on 25 April, 2015 in Nepal Himalaya, with a focal mechanism of low-angle thrust, determined unanimously by multiple research agencies. More than 100 aftershocks occurred thus far, including strong ones with magnitude larger than M s7.0, triggered normal-mechanism swarms hundreds of kilometers northeast of the epicenter in Tibet. The mainshock, located in central Himalayan orogenic belt and within the ‘seismic gap’ between the ruptured zones of the 1934 Bihar M w~8.1 and 1505 Lo Mustang M w~8.2 earthquakes, is the largest one on the Main Himalaya Thrust since 1950 Assam M w~8.4 earthquake. To help a better understanding of the earthquake, we provide in this paper a review on the tectonic setting and geometry of the Himalayan fault system, large historical earthquakes and their rupture areas, pattern of modern microseismicity, general models of seismic cycle in the Nepal Himalaya, and spatial pattern of surface deformation resulted from interseismic loading and coseismic slip. Combining the overall features of coseismic rupture of the mainshock from teleseismic finite fault solutions, we comment on this earthquake regarding to its relationship with the characteristic(typical topography-building) Himalayan events, the comparison with the 2008 Wenchuan M w 7.9 earthquake of similar magnitude, the general condition for low-angle thrust-type rupture reaching surface, and its implication to regional seismic hazard.更多还原