A Mw 6.6 earthquake struck Menyuan, Qinghai, China, on 7 January 2022. To determine the rupture parameters of this event, the coseismic InSAR deformation fields were mapped and further employed to estimate the focal mechanism. The best-fitting solution emphasized that the 2022 Menyuan earthquake ruptured at the junction of the Tuolaishan fault and the Lenglongling fault. Both rupturing faults were dominated by sinistral strike-slip, and the main slip was concentrated on the shallow part of the rupture plane. The latter was the main rupture segment with a strike of 106° and a dip of 86°. The slip mainly occurred at depths of 0–8 km, and the rupture was exposed at the surface. The maximum slip reached ~3.5 m, which occurred mainly at a depth of 4 km. Joint analysis of the optimal slip model, relocated aftershocks, Coulomb stress change, and field observation suggested that the strain energy in the Tuolaishan fault may not have been fully released and needs further attention. Moreover, the 2022 Mw6.6 Menyuan earthquake caused a significant stress loading effect on the western Tuolaishan fault and eastern Lenglongling fault, which implies that the 2022 event increased the seismic hazard in these regions.
The Nyainrong microcontinent carries key information about the ongoing evolution of the central Tibetan Plateau. The 2021 Mw 5.7 Nagqu earthquake is the largest instrumentally recorded event inside this microcontinent, which provides an ideal opportunity to elucidate the influence of this ancient microcontinent on the seismogenic mechanisms, stress heterogeneity and strain partitioning across the Tibetan Plateau. Here, we constrain the seismogenic fault geometry and distributed fault slip using Interferometric Synthetic Aperture Radar (InSAR) observations. By using the regional focal mechanism solutions, we invert the stress regimes surrounding the Nyainrong microcontinent. Our analysis demonstrates that the mainshock was caused by a normal fault with a comparable sinistral strike-slip component on a North-West dipping fault plane. The Nyainrong microcontinent is surrounded by a dominant normal faulting stress regime to the northeast and a dominant strike-slip stress regime to the southwest. Moreover, the clockwise rotation of the maximum horizontal stress (SHmax) from the southwest to the northeast is ~20°. This indicates that the Nyainrong microcontinent is involved in the mainshock occurrence as well as regional stress heterogeneity, and strain partitioning. Our results highlight the significance of the ancient microcontinent in the tectonic evolution of the Tibetan Plateau.
On 19 March 2021, the Ms 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.
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