Relocation of the MS 5.7Earthquake Sequence in Songyuan, Jilin Province, 2018 and theAnalysis of Its Seismogenic Structure

摘要

The 2018, Songyuan, Jilin MS5.7 earthquake occurred at the intersection of the Fuyu-Zhaodong fault and the Second Songhua River fault.The moment magnitude of this earthquake is MW 5.3, the centroid depth by the waveform fitting is 12km, and it is a strike-slip type event.In this paper, with the seismic phase data provided by the China Earthquake Network, the double-difference location method is used to relocate the earthquake sequence, finally the relocation results of 60 earthquakes are obtained.The results show that the aftershock zone is about 4.3km long and 3.1km wide, which is distributed in the NE direction.The depth distribution of the seismic sequence is 9km -10km.1 -2 days after the main shock, the aftershocks were scattered throughout the aftershock zone, and the largest aftershock occurred in the northeastern part of the aftershock zone.After 3 -8 days, the aftershocks mainly occurred in the southwestern part of the aftershock zone.The profile distribution of the earthquake sequence shows that the fault plane dips to the southeast with the dip angle of about 75°.Combined with the regional tectonic setting, focal mechanism solution and intensity distribution, we conclude that the concealed fault of the Fuyu-Zhaodong fault is the seismogenic fault of the Songyuan MS5.7 earthquake.This paper also relocates the earthquake sequence of the previous magnitude 5.0 earthquake in 2017.Combined with the results of the focal mechanism solution, we believe that the two earthquakes have the same seismogenic structure, and the earthquake sequence generally develops to the southwest.The historical seismic activity since 2009 shows that after the magnitude 5.0 earthquake in 2017, the frequency and intensity of earthquakes in the earthquake zone are obviously enhanced, and attention should be paid to the development of seismic activity in the southwest direction of the earthquake zone.