Seismotectonics and seismogenesis of the 2022-2023 Sichuan Luding MS 6.8,MS5.0 and MS5.6 earthquake sequences
The 2022 Sichuan Luding MS6.8 earthquake occurred on 5 September 2022,followed by two strong aftershocks of MS5.0 and MS5.6 on 22 October 2022 and 26 January 2023,respectively.These three earthquakes occurred in close proximity both spatially and temporally,with their epicenters several kilometers apart but distinct focal mechanisms.Therefore,it is crucial to investigate the seismogenic structures and mechanisms associated with these earthquakes.In this study,the Luding earthquake sequences were relocated using the double-difference relocation algorithm,and 79 moment tensor solutions for earthquakes with local magnitude greater than 2.5 were determined by the waveform inversion method and the P-wave polarity inversion method.Our findings show that the main rupture occurred along the Moxi fault of the Xianshuihe fault zone,where the aftershock activity is less.The 2022 Luding earthquake sequence occurred on the nearly vertical Moxi fault,exhibiting obvious segmental characteristics,and the average depths of the sequence gradually increase from NW to SE.The mainshock occurred on a strike-slip fault and the focal mechanisms of aftershocks along the Moxi fault are similar to the mainshock.The occurrence of the M6.8 mainshock can be attributed to the stress destabilization of the Xianshuihe strike-slip fault zone caused by the extrusion and rotation of the India-Eurasia plate.The aftershocks beneath the Gongga Mountain area were cluster activities triggered by the MS6.8 mainshock,with diffusely distributed locations and of small magnitude.They were likely the result of the MS6.8 mainshock triggering a series of secondary blind faults,Gongga Mountain fault zone,which are subparallel to the main fault,but not triggering the Yanzigou,Hailuogou,and Mozigou secondary faults,which are conjugate to the main fault.The Luding MS5.0 and MS5.6 earthquake sequences occurred on this blind fault with a dip of 40°～50°,which is shallower than the Moxi fault.The focal mechanisms in the Gongga Mountain area is obviously different from the strike-slip type of Xianshuihe fault zone,which may be caused by the rapid uplift of Gongga Mountain under the compression and rotation of Indio-Eurasian plate and the rapid stripping of the surface,resulting in local collapse due to gravity unloading.The MS6.8 mainshock has an obvious triggering effect.The occurrence of these Luding strong earthquakes released some stress accumulation in Moxi fault and Gongga Mountain area,but did not change the possibility of strong earthquakes occurring in the intersection area of"Y"shape.
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