Shallow coseismic slip and downdip afterslip associated with the 2022 M_W6.7 Menyuan (China) earthquake

Investigating the spatial distribution of coseismic rupture, postseismic afterslip, and their interactions is essential for understanding the heterogeneous frictional characteristics of faults, and seismic hazard assessments. This study offers a comprehensive analysis of both seismic and aseismic slip of the 2022 M_W6.7 Menyuan earthquake, which took place at the western terminus of the Tianzhu seismic gap located in the northeastern Qinghai-Xizang Plateau. By integrating near-field GNSS measurements, InSAR line-of-sight (LOS) displacements, and surface rupture data, we refined the coseismic slip distribution using a kinematic inversion and a mechanically constrained model. Our results reveal an unexpectedly large coseismic slip of about 3.3 m at shallow depths (less than about 6 km), along with minimal shallow slip deficit—features rarely observed in earthquakes of similar magnitude globally. The mechanically constrained approach yields a static stress drop of about 6.4 MPa. Additionally, we invert for the afterslip distribution from cumulative postseismic GNSS displacements recorded during the initial 2.7 years subsequent to the mainshock. The afterslip is predominantly situated downdip of the coseismic rupture zone, releasing 28.5% of the coseismic moment. There is a tight correlation between the spatiotemporal evolution of aftershocks and the downdip afterslip, with limited contributions from viscoelastic relaxation and poroelastic rebound which indicates that the afterslip mechanism primarily controls early postseismic deformation.