2017年8月8日九寨沟MS7.0地震构造与震区三维断层初始模型

摘要

2017年8月8日在四川省九寨沟县发生1次MS7.0地震.震后的野外地质调查没有发现同震断层破裂带;初步认为发震断层是1条隐伏的活动断层.文中根据九寨沟小震重定位结果,基于 SKUA-GOCAD软件平台对发震断层进行三维模拟和刻画,初步给出了发震断层的三维模型.发震断层三维结构显示九寨沟主震发生在断层面弯折部位,这与1973—1976年松潘强震序列的断层几何结构相似,表明强震活动可能与断层面的非均一性密切相关.同时收集并整理了九寨沟震区的历史强震(M≥6.5),以及活动断裂地表分布几何学、运动学特征,构建了震区10条主要活动断裂的三维断层初始模型,并分析和探讨了三维活动断层建模存在的局限性.九寨沟震区活动断层地下三维空间模型的建立,可以为分析历史地震的发震构造、探讨地震与活动断层之间的属性和关系、以及强震预判等提供依据.%On 8 August 8 2017,an MS7.0 earthquake occurred in Jiuzhaigou County,Sichuan Province. Field geological investigations did not find any co-seismic surface rupture in the epicenter area, implying that the seismogenic structure is likely a hidden active fault.Based on the results of the relocated aftershocks,the seismogenic fault was simulated and characterized using the SKUA-GOCAD software.The three-dimensional model of the seismogenic fault was preliminarily constructed,which shows that the main shock of the Jiuzhaigou MS7.0 earthquake occurred at the sharp bending area of the fault surface,similar to the geometry of the active fault that generated several major earthquakes in the Songpan area during 1973-1976.Our study suggests that high seismicity of this area may be closely related to the inhomogeneous geometry of the fault surface.In this work,we collected the historical earthquakes of M≥6.5,and analyzed the geometric and kinematic features of the active faults in the study area.A three-dimensional fault model for the 10 main active faults was constructed, and its limitation in fault modeling was discussed.It could provide evidence for analyzing the seismotectonics of historical earthquakes,exploring the relationships between earthquakes and active faults,and predicting major earthquakes in the future.