InSAR deformation observation and regional severe earthquake hazard analysis of the 2016 and 2022 strong earthquake activities in Menyuan,Qinghai
[Objective]Over the past 30 years,Menyuan Country,Qinghai,has experienced three strong earthquakes,demonstrating active seismic activity.The focal mechanisms of these earthquakes showed remarkable differences and the epicenters were all located near the Lenglongling fault.[Methods]In order to quantitatively analyze the activity characteristics of the Menyuan seismic sequence using InSAR technology to obtain the coseismic deformation field of the Menyuan earthquake of 2016 and 2022 and establish an appropriate fault model,the fine slip distributions of the two earthquakes were obtained through steepest decent method(SDM).Furthermore,the static Coulomb stress changes on the faults in the region and its surroundings caused by the Menyuan Mw 6.6 earthquake in 2022 were evaluated.[Results]The coseismic deformation field in 2016 exhibited a single elliptical uplift center,with predominantly thrust motion.In contrast,the spatial distribution of the deformation field in 2022 was more complex,showing a Y-shaped distribution,and there was a slight variation in the rupture direction from west to east,with primarily horizontal deformation.[Conclusion]The two earthquakes also differed in their slip patterns and shallow and deep structural styles.In 2016,the seismic activity was weak,with a slip zone existing at depths between 8 km and 12 km,where the maximum slip was only 0.23 m.The fault plane had a low inclination angle,which is a characteristic of deep-seated slip.By contrast,the 2022 earthquake was a typical shallow-focus earthquake featuring three distinct slip areas.The primary rupture occurred in the Lenglongling section,concentrated in the shallow part from 1 km to 7 km,with a maximum displacement of 3.22 m.A significant slip also occurred along the western extension of the Lenglongling fault,reaching a maximum slip of 2.59 m.The Tuolaishan section experienced rupturing mainly between 3 km and 8 km,with the maximum slip recorded as 2.1 m.[Significance]Combined with the analysis of the Menyuan earthquake activity in 1986,it is inferred that the Menyuan earthquake sequence is dominated by the activity of the Lenglongling fault,which is continuously adapting to new structures and stress adjustments in its northeast extension and shows compressive-shortening activity trend.The 2022 Menyuan Mw 6.6 earthquake had a significant impact range,and earthquake hazards need to be continuously monitored and studied further,especially in areas where static Coulomb stress changes exceed the hazard threshold.
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