Conjugated strike-slip faults during the Yangbi,Yunnan Ms6.4 earthquake sequence on May 21,2021
Using earthquake catalog and seismic waveform data from the national earthquake cata-loging system,the double-difference relocation algorithm was applied to relocate the Yangbi Ms6.4 earthquake sequence that occurred on May 21,2021(spanning from May 18 to October 31,2021;ML＞0.0).This relocation process determined the precise source locations of 7 138 seismic events.Additionally,the cut-and-paste inversion method for focal mechanism waveforms was used to obtain the focal mechanism solutions for 39 earthquakes with Ms≥3.0 in the se-quence,providing insights into the structural details and clearly defining conjugate fault traces.Combined with field geological surveys of the earthquake sequence distribution area,the rupture process and faulting mode of the strike-slip earthquake were analyzed.Results indicate the follow-ing:(1)The fault associated with the Yangbi Ms6.4 mainshock comprises a group of right-lateral strike-slip fault zones,approximately 5 km wide,60 km long,and oriented with a strike of ap-proximately 130°,dipping to the southwest.The fault exhibits a simple shear pattern,with sec-ondary conjugate faults,including the R shear rupture,R'shear rupture,and extensional rup-tures,developing on both sides of the main fault.The distribution of the earthquake sequence is strongly influenced by the simple shear,displaying a monoclinic symmetry.Specifically,the east-ern side of the northern end and the western side of the southern end of the earthquake sequence exhibit broom-like and horsetail-like distribution patterns,while noticeable seismic quiet areas are observed on the eastern side of the southern end and the western side of the northern end.Strong earthquakes Ms≥5 are concentrated in the intersection areas of the conjugate faults and the main fault.(2)The entire seismic sequence is distributed along the Mesozoic sedimentary strata along the western side of the Weixi-Qiaohou fault.The extension direction of the main fault forms a certain angle with the Weixi-Qiaohou fault,and the fault properties notably differ from those of the Zuobaida fault.Therefore,the seismogenic structure of the Yangbi Ms6.4 earthquake comprises a group of relatively independent hidden faults between the Weixi-Qiaohou fault and the Zuobaida fault.
Yangbi Ms6.4 earthquake in 2021relocationfocal mechanismconjugate faultsimple shear
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