关键词: 2020年伽师地震, 双差重定位, W震相, 矩张量反演

Abstract: As the most active and spectacular intracontinental mountain ranges in Central Asia, Tian Shan is a natural laboratory to explore and understand the geodynamic processes involved in intracontinental mountain building. The origin of Tian Shan can be traced back to the collision and accretion of several micro-continents, island arcs, and accretionary prisms initiated in the Paleozoic. This tectonic activity continued into the Mesozoic. From the Cretaceous to the early Tertiary, the mountain ranges were eroded and reduced to a flat plain. Then, in the later Tertiary, uplift was rejuvenated as a far-field consequence of the India-Eurasia collision, and continues to present day, characterized by the active seismicity in Tienshan in modern times. The geology of present-day central Tian Shan is mainly composed of intermontane basins and subparallel ranges, separated by the east-west striking Cenozoic active thrust faults stretching approximately 2 500km in length. On the southern and northern margins of the Tian Shan Range, the Tarim Basin and the Kazakh Shield act as stable blocks. Situated in the southwest foreland of Tien Shan, the Kashgar region is a seismic active area since the 20^th century, several strong earthquakes stroke the region and the surround areas, causing severe damage to the local residents. In this study, we apply the double-difference relocation technique and W-phase method to relocate the 19 January, 2020 Xinjiang Jiashi earthquake, and to determine the focal mechanisms using data provided by China Earthquake Networks Center. The relocated epicenters of the 2020 Jiashi earthquake sequence show two dominant spatial distribution directions. The major NWW-trending spatial distribution shows a Kepingtage Fault-paralleled narrow belt stretching about 34km, with most of aftershocks distributed in the northern side of the fault. The secondary spatial distribution shows a NNW-striking belt stretching about 8km. The depth profiles show a predominant epicentral depth at the range of 10~20km. The focal parameters for the 19 January, 2020 Xinjiang Jiashi M6.4 earthquake are: strike 76°, dip 81°, rake 109° for the nodal plane Ⅰ, and strike 190°, dip 21°, rake 26° for nodal plane Ⅱ, and the moment magnitude is M_W5.87. The focal parameters indicate that the earthquake event is characterized by dominant thrust with minor strike movement. Combined with the analysis of the relocated epicentral locations, focal mechanisms and geological settings, it is inferred that the seismogenic fault of the 19 January 2020 Jiashi M6.4 earthquake is the west segment of the near E-W trending Kepingtage thrust fault.

Key words: the 2020 Jiashi earthquake, double-difference relocation, W-phase, moment tensor inversion