中文摘要：

由于印度-欧亚板块碰撞,位于板块边界带的喜马拉雅地区大震频繁,但对其活动性的认识仍十分有限.2015年4月25日尼泊尔中东部地区时隔80年再次发生8级地震,为研究板缘地震提供了一次难得机遇.本文用西藏和尼泊尔的GPS连续观测数据和全球分布的远震地震波记录联合反演此次特大地震的破裂过程,结果显示此次地震发生在印度板块与青藏高原接触边界面——喜马拉雅主滑脱断层上.北倾11°、近东西（295°）走向的断层面破裂约100km长（博卡拉到加德满都）,130km宽（从加德满都深入我国西藏吉隆县）,破裂以逆冲滑动为主,平均幅度达到2.4m,释放的地震矩高达9.4×1020 N·m.反演结果还显示,震源体主要破裂分布深度范围为5~25km,应无地表破裂,属于一次盲地震.基于GPS资料推测的地壳现今运动速率及1833年地震的震源位置,我们推测地震在此次地震破裂区域复发的周期可能为150~200a,而极震区以南的深部滑脱断层仍保持闭锁,未来仍有导致灾害性大震的可能性.

英文摘要：

On 25 April 2015,a devastating（MS8.1）earthquake struck the central Nepal,causing severe damages in Kathmandu.The earthquake is believed to occur on a basal detachment faultalong which the Indian plate plunged under Tibet,providing a rare opportunity to understand seismicity of the continental plate boundary.Strong ground motions and permanent surface displacements induced by this event were observed unprecedentedly by continuous GPS networks in Nepal and Tibet,and these geodetic observations close to the rupture zone are important as such when a finite fault model of rupture is constructed to characterize rupture processes and source properties.In this work,we focus on retrieving the slip distribution and temporal history of this earthquake through a joint inversion of teleseismic waveforms and near-field GPS data.We derived 12 static coseismic offsets of GPS sites in Nepal and Tibet and retrieved 5seismograms of strong motions recorded by high-rate（1Hz）GPS sites in Tibet.In addition,we chose a total of 43P-wave waveforms from global seismic networks to enhance the spatiotemporal resolution of source model.The fault geometry is prescribed on a subsurface plane that is buried at 5~30km depths with a dip of 11°to the north and a strike of 295°,consistent with the USGS CMT solution and structural geology.This rectangular model plane in dimensions of 210km×160km was further divided into 21×8matrix of sub-faults.The finite source modeling assumes that the rupture processes can be approximated by abrupt rise of slip on these subfaults in the wake of rupture front that passages successively through them from the hypocenter.The rupture velocity across adjacent subfauts is assumed to be a constant at 2.5km·s-1.For each subfault,the slip growth is represented by a source time function that is parameterized by 5overlapping triangles with a 2sec half-time duration,each shifted by 2sec.Seismic moments of all triangles,each corresponding to a subevent,are unknown parameters to be solved with the non-negative least