The Luding Ms6.8 earthquake on September 5,2022,marked the largest destructive quake in the vicinity of the Xianshuihe fault in recent six years,providing crucial insights into potential strong seismic activity along the eastern boundary of the Chuandian block.This study employed hypoDD method to precisely locate 11,103 earthquakes in the Luding region from 2009 to 2022.Waveform fitting techniques were then utilized to derive focal mechanism solutions for the mainshock,12 aftershocks ≥Ms3.0,and two strong earthquakes≥Ms5.0 near Gongga Mountain.The results revealed that the Luding Ms6.8 earthquake originated from the Moxi fault,specifically along the Heigou—Yanzigou—Tianwan section.This quake cover a previously sparse seismic activity gap along the Moxi fault,spanning approximately 40 kilometers and trending at～160°,exhibiting a nearly vertical orientation.The aftershocks along the fault were primarily of the left-lateral strike-slip type.Since 2009,there has been continuous seismic activity near Gongga Mountain to the west of the Luding earthquake,peaking in 2015.Following the mainshock,shallow seismic activity around Gongga Mountain intensified,characterized by tensile fracturing.Notably,these shallow events were triggered and distinct from the seismicity along the Moxi fault.Analysis of b-values indicates distinct stress segmentation along the Moxi fault.The southern and eastern segment,from Wandong to Tianwan,exhibited low b-values(～0.5),whereas the northern and western segment,from Wandong to Heigou,showed higher b-values ranging from 0.8 to 1.0.This indicates that the stress on the Moxi fault zone has obvious segmented characteristics,with energy mainly concentrate and release from Yanzigou to Tianwan.
Luding EarthquakeMoxi faultEarthquake relocationFocal mechanismb value
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