Discussion on seismogenic structure and mechanical mechanism of the 1 June 2022 M_S6.1 Sichuan Lushan earthquake

The 2022 M(S)6.1 Lushan earthquake struck Lushan country, Ya'an city in Sichuan Province, China on June 1 at 17:00:08 (Beijing time). This earthquake occurred in Longmenshan fault zone after the 2008 M(S)8.0 Wenchuan earthquake and the 2013 M(S)7.0 Lushan earthquake, and only 9 km away from the Lushan event. To reveal the seismogenic structural characteristics of this earthquake and its possible relationship with the 2013 M(S)7.0 Lushan earthquake, and further understanding the dynamic process and seismic risk of strong earthquake in Longmenshan fault zone, we used CAP full waveform inversion method to calculate the focal mechanism solution of the M(S)6.1 Lushan earthquake, and relocated the aftershock events of the 2013 Lushan M(S)7.0 event using a hybrid multi-stage method, and further discussed the stress trigger relationship of the two events based on Coulomb stress change. The results show that the focal mechanism solution of the M(S)6.1 Lushan earthquake is: the strike, dip and slip angles of nodal plane I are 221 degrees, 40 degrees and 105 degrees, and the parameters of nodal plane II are 22 degrees, 52 degrees and 78 degrees respectively, the centroid depth is 14 km, and the fault plane solution of the focal mechanism shows a similar nodal plane to that of the Longmenshan fault zone. The inversed azimuth and dip angle of P-axis are 120 degrees and 6 degrees, reflecting that the earthquake was mainly affected by NWW-SEE horizontal compression stress, which is consistent with the background tectonic stress field of the southern section of the Longmenshan fault zone. The seismic relocation demonstrates that the M(S)6.1 Lushan earthquake occurred on a SE-dipping back-thrust fault on the NW side of the seismogenic fault of the 2013 M(S)7.0 Lushan earthquake, suggesting that the nodal plane II is the fault plane. Finally we calculate the Coulomb stress change caused by the 2013 M(S)7.0 Lushan earthquake on the fault plane of the M(S)6.1 earthquake, and found the maximum Coulomb stress change reaches 1.5 MPa, indicating that the significant triggering effect between them.