The surface rupture zone is the direct manifestation of an earthquake on the Earth's surface,and its width is an important parameter for the active fault's"avoidance zone"and seismic engineering design.The development of remote sensing technology such as unmanned aerial vehicle detection has promoted the research of surface rupture zone,including obtaining high-resolution image data,accurately measuring their width,analyzing their spatial distribution,and defining a reasonable"avoidance zone"for the active fault.The 2022 Menyuan Ms6.9 earthquake created a significant left-lateral surface rupture zone in the stepover of the Lenglongling and Tuolaishan faults along the northeastern margin of the Tibetan Plateau.In this study,we conducted a detailed interpretation of the earthquake's surface rupture zone based on high-resolution unmanned aerial vehicle orthoimages and digital elevation models obtained after the earthquake.We measured the rupture zone's width every 100 m along the fault strike and got 251 width data points.The maximum and average width of the R1 rupture zone are 209.78±14 m and 42 m respectively and are 115.31±15.72 m and 26.14 m at the R2 rupture zone respectively.According to the spatial distribution of the above data,we believe that the surface rupture zone's width shows significant variations along the fault strike,which is mainly controlled by the distribution of Quaternary loose deposits,the geometric structure of the faults,and their coseismic deformation.Specifically,the surface rupture zone is wider in the areas with Quaternary loose deposits,complex fault structures,and larger coseismic displacement,while it is narrower in the areas with the fault cut through bedrock,relatively straight fault segments,and smaller coseismic displacement.Based on the statistics of the rupture zones'width after removing the data's outliers,we conclude that the effective widths at 95.4％and 68.2％confidence intervals are approximately 70 or 50 m,respectively.For this reason,we suggest that the"avoidance zone"in the seismic engineering design can refer to the effective widths of fault zones in this study(70 or 50 m)if the maximum potential magnitude of a strike-slip fault is similar to the Menyuan earthquake(approximately M7.0).Specifically,the width of the"avoidance zone"can expand 35 or 25 m according to the type of building or structure on each side of a single strike-slip fault or the domain of complex geometric structures such as oblique stepover,sub-parallel secondary faults on both sides,strike curved faults,and the areas with steeply inclined fault plane.This study provides a basis for the avoidance of strike-slip faults in the choice of building location.
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