2019年西藏墨脱MS6.3地震震源参数及其构造意义

北京时间2019年4月24日04∶15，西藏自治区林芝市墨脱县发生了M_S6.3地震，该地震位于印度板块与欧亚板块俯冲碰撞的东北犄角地区，构造背景十分复杂.本研究基于我们在东喜马拉雅构造结地区架设的宽频带地震台站记录的近震波形数据，结合中国和国际地震台网的波形和到时资料，对该地震的震源位置、震源机制解和破裂过程进行了重新确定.结果显示，此次墨脱6.3级地震发生在（94.56±0.01°E，28.41±0.01°N），震源深度为地表以下13.3±1.6（或海平面以下11.5±1.6）km.震源机制解走向/倾角/滑移角分别为202°/17°/20°，震源破裂较大的位置主要集中在初始破裂点NNE侧约5 km附近.结合其他地球物理和地质学资料，我们推测该地震位于主喜马拉雅逆冲断裂发生近90°突然偏转的大拐弯地区，桑构造结相对于其西侧南迦巴瓦构造结的西向俯冲和北向推挤是该地震发生的主要构造背景.

Source parameters of the 2019 MS6.3 Medog earthquake and its tectonic implications

An M_S6.3 earthquake occurred at Medog County, Nyingchi City, Tibet at Beijing time 04:15 on 24 April 2019. This earthquake is located in the northeast corner of the Himalaya orogenic belt where the Indian plate underthrusts beneath the Eurasian plate. Based on the waveforms recorded by the local broadband seismic stations we deployed at the eastern Himalaya syntaxis, and the waveform and traveltime data obtained from Chinese and international seismic networks, we determined the earthquake location, focal mechanism and rupture process. The resulting epicenter of this earthquake is (94.56±0.01°E, 28.41±0.01°N) and the focal depth is 13.3±1.6 km below the surface (or 11.5±1.6 km beneath the sea level). The focal mechanism solution strike/dip/slip is 202°/17°/20°. The large rupture is mainly concentrated about 5 km to the NNE of the initial rupture area. Combined with other previous geophysical and geological studies, we infer that the earthquake occurred at the rapid turning area where the Main Himalayan thrust suddenly rotated nearly 90°. The major tectonic feature for this area is the west-dipping subduction and northward thrust of the Sang syntaxis with respect to the Namche Barwa syntaxis.