2020年龙泉山断裂带MS5.1地震成因综合分析

2020年2月3日四川省成都市青白江区发生M_S5.1地震,震中烈度为Ⅵ度。该地震事件震中位于龙泉山断裂带上,距离成都市中心38 km,是龙泉山断裂带历史上非常罕见的5.0级以上地震事件。针对该事件成因进行了综合分析与研究,具体内容包括:(1)通过收集历史地震资料讨论龙泉山断裂带的地震活动性;(2)利用高质量的波形数据对主震位置进行重定位;(3)根据地震层析成像获得的三维vP、vS以及泊松比(σ)模型分析了孕震构造和流体影响,以及(4)利用固体潮理论模型分析了固体潮与地震触发的相关性。结果表明,本次M_S5.1地震发生在龙泉山断裂带北段,震中坐标为(30.732°N,104.529°E),震源深度为15.12 km;震源位于高-低泊松比过渡带附近,并伴随着大范围的低速异常,初步推断与深部流体有关;同时,固体潮在断层面上产生的剪切应力变化,也可能与本次地震的触发密切相关,暗示着在地震发生前龙泉山北段的地震危险性已经达到了较高水平。因此深部流体侵入作用、强震同震效应以及特定孕震构造环境的综合影响可能是导致本次地震触发的主要因素。

Comprehensive Analysis of Seismogenesis of the 2020 MS5.1 Earthquake on the Longquanshan Fault Zone, SW China

On Feb 3,2020,an M_S5.1 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 M_S5.1 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.