| Abstrakt: |
The N‐S‐trending grabens, the most prominent active structures in the Tibetan plateau, contain important information about the evolution and deformation mechanism of the plateau. The Ms6.6 earthquake that occurred in Nima, Qiangtang on July 22, 2020, provides an opportunity to investigate the kinematics of the grabens. Here, we use field survey and interferometric synthetic aperture radar to study the structural style, coseismic and postseismic deformation, fault slip, and stress changes of the Nima earthquake. The N‐S‐trending Qomo Ri graben (QRG) and the normal faults on the east and west sides are kinematically correlated with the NE‐trending sinistral Jiangaizangbu River and West Yibug Caka faults. The QRG is characterized by an extensional strike‐slip duplex and negative flower structure. The maximum coseismic deformation of the Nima earthquake is 29.4 cm in the line‐of‐sight direction observed by Sentinel‐1 ascending images. The coseismic slip model demonstrates that the NE20–30°‐striking fault caused the Nima earthquake has a maximum slip of 1.39 m and a main slip area at 4–12 km depth. The seismological fault may transit from a moderately dipping normal fault near the surface to a steeper strike‐slip fault at depth. Obvious postseismic deformation was observed in the stress‐enhancement area. The afterslip model shows that the mainshock fault is correlated with parallel normal faults to its west. We infer that the QRG was formed by local E‐W‐trending extension at the joints of the left‐stepping sinistral fault system, and the active normal faulting in the Qiangtang block favors stress localization. Plain Language Summary: On July 22, 2020, an Ms 6.6 earthquake occurred in Nima, Qiangtang, Tibet, China and caused surface deformation. We use satellite images to map the large deformation that appeared at the earthquake time and the smaller‐magnitude deformation after the earthquake. Based on the obtained deformation and geological mapping results, we establish fault models and analyze the geometry and kinematics of the faults, their structural origins, and the influence of the 2020 Nima earthquake. We infer that the causative fault structurally links the strike‐slip faults to the south and north of the epicenter. In addition, the fault activity of the Nima earthquake in the Qiangtang block may increase earthquake risk in surrounding areas. Key Points: The seismogenic fault may change from normal‐slip kinematics in the near‐surface to strike‐slip motion at depthThe N‐S‐trending grabens in Qiangtang are characterized by negative flower structuresThe active normal faults favor stress localization and probably propagate laterally into sinistral strike‐slip faults [ABSTRACT FROM AUTHOR] |
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