据中国地震台网测定,2021年5月22日青海省果洛藏族自治州玛多县发生7.4级地震,震中位于青藏高原中部的巴颜喀拉块体,不同于其他7级地震往往多发生在块体边界带上,此次地震是发生于巴颜喀拉块体内部区域的一次强震。本次典型块体内部大地震的发生意味着块体的相互作用加剧,引起了学者们广泛关注。本文利用GNSS和Sentinel-1 InSAR数据获取了玛多地震的同震形变场,并以此为约束,选用弹性半无限位错模型,反演了玛多地震的同震位错分布。升、降轨InSAR同震形变场显示玛多地震造成了显著的地表形变,升轨最大LOS向位移达1.1m,降轨最大LOS向位移达0.9m。研究结果表明,该地震造成了明显的长度约160km的地表破裂。断层面位错分布反演结果显示,发震断层由主断层和分支断层组成,主断层倾向北,倾角85°,平均滑动角-11.25°,分支断层倾向南,倾角68°,平均滑动角-11.39°。同震优势滑动分布区域主要分布在地下0～17km深度范围,最大滑动量约为4.34m,位于断层东侧东草阿龙段,反演得到的矩震级为M_W7.4。发震断层破裂多个凹凸体,且该地震是一次不对称的双侧破裂事件。综合地球物理及地质资料分析认为,主发震断裂为靠近巴颜喀拉块体北边界的昆仑山口—江错断裂。震中区域形变结果显示,此次玛多地震增强了巴颜喀拉块体在东北部地区挤压应力积累的特征,表现在东昆仑断裂玛沁段应力有所增加,值得后续深入研究和关注。

According to the China Earthquake Network,a magnitude 7.4 earthquake struck Madoi County in the Guoluo Tibetan Autonomous Prefecture of Qinghai Province on May 22, 2021. The epicenter was located within the Bayan Har block,situated in the central region of the Tibetan Plateau. Unlike typical magnitude 7 earthquakes,which generally occur along block boundary zones,this was a significant intra-block event,prompting widespread interest in whether the earthquake indicates block disintegration or heightened stress accumulation within the block. In response to this,our study utilized GNSS and Sentinel-1 InSAR data to calculate the isoseismic deformation field of the Madoi earthquake. This data served as a constraint in inverting the subsurface dislocation distribution along the seismogenic fault using an elastic semi-infinite dislocation model. The InSAR coseismic deformation fields revealed substantial surface deformation,with maximum line-of-sight(LOS) displacements of 1.1 meters on the ascending track and 0.9m on the descending track. Our findings indicate that the earthquake produced a significant surface rupture stretching approximately 160km,extending from the Changma River in the east to Lake Ereung in the west. The coseismic slip model results suggest that the seismic fault system comprises a main fault and a secondary fault. The main fault dips northward at an angle of 85° with an average slip angle of -11.25°,while the secondary fault dips southward at an angle of 68° with an average slip angle of -11.39°. The seismic rupture was primarily concentrated between 0 and 17km depth,with a maximum slip of approximately 4.34 meters. The moment magnitude derived from the inversion was M_W7.4. The rupture area contained four asperities and represented an asymmetric bilateral rupture event. Based on aftershock relocations,field investigations,and tectonic background analysis,we determined that the primary seismic rupture occurred along the Kunlunshankou-Jiangcuo fault. Furthermore,the earthquake significantly increased extrusive stress accumulation in the northeastern Bayan Har block,particularly along the Machin section of the East Kunlun Fault. These findings highlight the need for further in-depth study and monitoring of stress accumulation in the region.

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青海省重点研发与转化项目计划(2022-SF-138)资助