Abstract:On Feb 3, 2020, an MS5.1 earthquake occurred in Chengdu, Sichuan Province. The epicenter of the earthquake event is located on the Longquanshan fault zone, 38 km away from the center of Chengdu. As a rare earthquake event with M≥5.0 in the history of Longquanshan fault zone, a comprehensive analysis was carried out on the seismogenesis of this event: (1) The seismicity along the Longquanshan fault zone was discussed by collecting historical seismic data; (2) the location of main earthquake was relocated by using high-quality waveform data; (3) the seismogenic structure and fluid influence were analyzed through seismic tomography; (4) the relationship between the earth tide and the earthquake was analyzed by using the theoretical model of earth tide. The results showed that the MS5.1 earthquake occurred in the northern part of Longquanshan fault zone with epicenter coordinate of (30.732°N, 104.529°E) and focal depth of 15.12 km. The source is located near the transition zone of high-low Poisson's ratio, accompanied by a wide range of low velocity anomalies. Furthermore, the change of shear stress caused by the earth tide on the fault plane is also considered to be closely related to the triggering of the earthquake, which indicates that the seismic risk of the northern part of Longquanshan fault zone has reached a high level before the earthquake. This study suggests that the deep fluid intrusion, the coseismic effect of strong earthquakes, and the comprehensive influence of specific seismogenic and tectonic environment may be the main factors leading to the triggering of this earthquake.
