The Surface Process and Seismogenic Structure of the 2021 M-s 6.1 Biru, Central Tibet Earthquake

On 19 March 2021, the M-s 6.1 Biru earthquake occurred in central Tibet. Because of the limited number of stations, researchers have different understandings of the epicenter and the focal mechanism. In addition, when the earthquake occurred in a key location at the intersection of the strike-slip structure and the extensional structure in the Tibetan plateau, no seismogenic fault is associated with this earthquake, according to the known active faults. In this article, the focal mechanism solution, the meizoseismal area, the orientation of the long axis of the isoseismal lines, and the spatial distribution and geometric characteristics of earthquake fissures were obtained based on the Interferometric Synthetic Aperture Radar coseismic deformation field, inversion of the focal mechanism solution, and field investigation. The macroscopic epicenter was located approximately 13.17 km southeast from the instrumental epicenter, and the earthquake occurred in the seismotectonic background of south-north extrusion, east-west extension, and a mixture of strike-slip and normal faulting. The focal mechanism solution is the normal fault rupture of the northeast-trending main nodal plane. The earthquake caused regularly arranged coseismic ground fissures and damaged a myriad of buildings. The maximum intensity was VIII. The long axis of the isoseismal lines was in the northeast-southwest direction, thus showing a distinct hanging-wall effect. The seismogenic structure was a newly discovered northeast-trending normal fault with a partial sinistral component. The newly discovered seismogenic normal fault, together with the normal faults that have been identified in adjacent areas, is vital to the crustal deformation of the central Tibetan plateau.