Before and after the ML5.2 earthquake in Yanjin,Yunnan Province on 23 January 2021,several medium and small earthquakes occurred in this region.In order to better assess the seismic hazard and identify the seismogenic structures in this region,we use the waveform data of the near earthquakes from the Yunnan Seismic Network and the Sichuan Seismic Network to invert the focal mechanisms and the depths of the ML≥3.5 earthquakes in Yanjin by the cut-and-paste(CAP)method and two different velocity models.Then,we determine the depth of the ML5.2 earthquake using the depth phase sPn.Finally,we employ the double-difference relocation method to relo-cate the earthquake sequences in Yanjin.We obtain that seismogenic fault of the isolated ML 5.2 earthquake se-quence belongs to the thrust type.It strikes near the N-S direction and dips eastward at 50°.The ML5.2 earthquake has a shallow source,the rupture occurred from the bottom to the top along the fault plane.The seismogenic fault of the swarm-type ML3.9 earthquake sequence belongs to the strike-slip type.It strikes from NNW and dips north-eastward at about 80°.The focal mechanisms of the three ML≥3.5 earthquakes in this swarm-type sequence are slightly different,this may be due to the region's complex fault structure and stress environment.Based on this a-nalysis,we believe that the seismogenic fault of the ML3.9 earthquake sequence is the Yanjin-Junlian fault.The seismogenic fault of the ML5.2 earthquake sequence is an unknown hidden fault in the near N-S direction and with a dip angle of about 50°,which is generated by the Huayingshan fault and the Yanjin-Junlian fault.
关键词
盐津地震序列/震源机制解/重定位/sPn震相/发震构造
Key words
the Yanjin earthquake sequence/focal mechanism/relocation/sPn phase/seismogenic struc-ture
维普
万方数据