2016年和2022年青海门源强震活动的InSAR形变观测与区域强震危险性分析

InSAR deformation observation and regional severe earthquake hazard analysis of the 2016 and 2022 strong earthquake activities in Menyuan,Qinghai

30多年来青海省门源县先后经历了3次强震,显现出活跃的地震活动。3次地震的震源机制存在显著差异,且震中均位于冷龙岭断层附近。为定量分析门源地震序列的活动特征,利用InSAR技术测量2016年和2022年门源地震引发的地表形变,详细分析了同震形变场的空间特征及发震断层,并据此建立了断层模型,通过最速下降法(SDM)获得2次地震的精细滑动分布,最后基于静态库仑应力变化评估了2022年门源M_(W)6.6地震对该区域及周边断层的应力扰动。研究发现2016年地震同震形变场表现为单一的椭圆隆升中心,运动属性以逆冲为主;而2022年地震形变场空间分布较为复杂,呈Y型分布,破裂走向自西向东有轻微变化,以水平形变为主。2次地震的滑动模式和深浅构造样式也存在明显差异:2016年地震活动性弱,在深部8~12 km存在一个滑动区,最大滑动量仅有0.23 m,断层面倾角低,具有深部滑动特点;而2022年地震为典型的浅源地震,存在3个明显的滑动区域,主破裂发生在冷龙岭段,集中在浅部1~7 km,最大位错量为3.22 m,冷龙岭断层向西延伸段也发生了明显滑动,最大滑动量达到2.59 m,托莱山段破裂深度集中在3~8 km,最大滑动量为2.1 m。结合1986年门源地震活动分析,推断门源地震序列受冷龙岭断层活动支配,冷龙岭断层在北东向扩展以及挤压缩短的活动趋势中,不断适应新的构造和应力调整。2022年门源M_(W)6.6地震位错影响范围较大,地震危险性需持续关注和深入研究,尤其是静态库仑应力变化超过了危险性阈值的部分。

[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 M_(w)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 M_(w)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.