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相对稳定大陆地区超压流体驱动的地震活动: 2020年2月2日MS 5.1 青白江孤立型地震的启示
雷兴林1, 孙建宝2, 苏金蓉3
2020年2月2日在该断裂带北段发生一个M 5.1地震,是个孤立型地震。矩张量反演结果表明,矩心深度3.8公里,两个节面的走向/倾角/滑动角分别为205°/54°/96°和15°/36°/82°。没有对应的地表断层。根据InSAR数据得到了地表同震变形,并与两个震源机制解节面建立的断层位移模型的理论变形对比。同时,结合为数极少的小微震精定位结果,得到的结论为:西北倾向倾角54°的节面应该是震源断层,矩心的经纬度为(104.48, 30.71),震源断层长度约 2.8 km,深度范围 2到5 km。各种迹象表明,与四川盆地其它几个中强时空孤立型天然地震类似,该地震极有可能是受深部天然超压流体驱动的临界-亚临界断层活动所致。
关键词:  孤立地震,InSAR, 深部流体, 断层阀门机制,四川盆地
Fluid-driven seismicity in relatively stable continental regions: insights from the 3 February 2020 MS5.1 Qingbaijiang isolated earthquake
Xinglin Lei1, Jianbao Sun2, Jinrong Su3
1.National Institute of Advanced Industrial Science and Technology(AIST);2.State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration;3.Earthquake Monitoring Centre, Sichuan Earthquake Administration
On 3 February 2020, an isolated MS5.1 earthquake occurred in the northern section of the Longquanshan fault zone. We present the results of a study aimed at defining the geometry of seismogenic structures for this earthquake. Centroid moment tensor inversion results show that the focal depth was 3.8 km, and the strike/dip/rake angles for the two nodal planes were 205°/54°/96° and 15°/36°/82°, respectively. There was no corresponding surface fault. From the coseismic deformation of the surface, resolved from InSAR measurements, together with relocated hypocenters for a small number of aftershocks, it was concluded that a northwest-dipping nodal plane corresponded to the source fault. The fault was found to have a length of about 2.8 km and a depth range of 2–5 km, and the centroid for the earthquake was located at 104.48° longitude and 30.71° latitude. Various pieces of evidence point to the plausible scenario that this earthquake, similar to several other moderately sized natural earthquakes in the Sichuan Basin, was driven in part by fluid flow from nearby overpressure gas packets of natural origin.
Key words:  Isolated earthquake, InSAR, Deep fluid, Fault valve, Sichuan Basin