利用InSAR观测揭示2020年新疆于田MW6.3地震发震构造及对藏北裂谷生长的启示

正断层地震是青藏高原内的重要地震类型，该类型构造行为与高原的生长机制密切相关.2020年6月25日在新疆于田县发生了M_W6.3正断层地震，震中位于青藏高原巴颜喀拉块体西缘的贡嘎错断裂附近.震中附近在2008年至2020年间相继发生了4次M>6地震，其中3次为正断层事件.本研究中，我们利用Sentinel-1及ALOS2卫星的SAR数据，进行差分干涉技术（InSAR）处理和时序形变分析，获取了这次地震同震形变场及震后位移序列，并以此为约束，厘定了于田地震的断层几何参数.InSAR结果显示同震最大视线向位移约20 cm，半年内的震后累计形变达~3 cm，形变趋势与同震相似.反演结果显示，同震滑动主要集中在地表以下7 km，早期余滑出现在地表以下2 km且较之更陡的位置，暗示了发震断层可能具有铲形特征.同震和震后的连续形变，揭示了正断层地震在当地地形地貌改造方面的持续作用.综合青藏高原其他十余次正断层地震的研究结果，正断层倾角呈现从南向北逐渐增加，并与当地的扩展速率呈负相关趋势，预示正断层倾角可作为研究当地扩张演化的指示信息.

Seismogenic fault of the 2020 MW6.3 Yutian,Xinjiang earthquake revealed from InSAR observations and its implications for the growth of the rift in the North Tibet

Normal faulting (NF) earthquakes are important tectonic processes in the Tibetan Plateau, which is likely related to the growth of the Tibetan Plateau. On June 25, 2020, an MW6.3 NF earthquake occurred in Yutian, Xinjiang. The epicenter was located near the Gongga fault in the western Bayan Har structural junction in the northern Tibetan Plateau. From 2008 to 2020, four earthquakes of M>6 occurred in the Yutian area, three of which resulted from NF. In this study, we used the SAR data from Sentinel-1 and ALOS2 satellites to obtain the co- and post-seismic deformation in the Line of Sight (LOS) direction following the mainshock. Based on the InSAR LOS measurements, we determined the fault geometric parameters, coseismic slip and early afterslip of the Yutian earthquake using a two-step geophysical inversion strategy. The InSAR observations show continuous subsidence in the epicentral area through the co- and post-seismic processes, in which the maximum coseismic deformation reaches up to 20 cm, and the cumulative postseismic deformation in the first 6 months is greater than 3 cm. The modelling results show that the coseismic slip is concentrated at depth of 7 km, while the afterslip requires a shallower and steeper fault structure, implying that the earthquake fault may have a listric shape. We compiled over 10 NF earthquakes source parameters across the Tibetan Plateau. Their dip angles gradually increase from south to north, while they are inversely correlated to the geological extension rates. This further indicates that the dip of a normal fault can be an indicator of the progress of the rift growing.