Co- and post-seismic deformation of the 2022 Menyuan <i>M</i>w6.6 earthquake from InSAR and GPS observations

SUMMARY This study combines InSAR (Interferometric Synthetic Aperture Radar) and GPS (Global Positioning System) data to examine the coseismic slip and post-seismic deformation of the 2022 Menyuan Mw 6.6 earthquake, shedding light on the fault structure, slip distribution and rheology of the northeastern Tibetan Plateau. InSAR coseismic deformation revealed fault dip angle of 82° for the Lenglongling fault and 84° for the Tuolaishan fault. The optimal coseismic slip model, derived from InSAR, GPS and near-field pixel-offset data, indicates a maximum slip of 3.3 m, concentrated in the upper 3 km of the fault. We propose a three-step procedure to comprehensively invert the post-seismic deformation, accounting for both afterslip and viscoelastic relaxation, constrained by the InSAR and GPS observations. The optimal afterslip model indicates a cumulative afterslip of 9 cm over two years, primarily concentrated in the deeper sections of the coseismic slip zone. Incorporating viscoelastic relaxation improved the spatial distribution of the afterslip on the Tuolaishan fault. The afterslip released a seismic moment of 1.96 × 10¹⁸ N·m, accounting for approximately 15 per cent of the coseismic moment release. The viscosity of the lower crust in the region was estimated to range from 1.5 to 5 × 1018 Pa·s, with an optimal value of 2 × 10¹⁸ Pa·s. As the distance from the epicentre increased, viscoelastic relaxation became the dominant post-seismic mechanism, contributing up to 80 per cent of the deformation observed at the QHGC and GSMI stations. Additionally, the earthquake increased Coulomb stress on the ‘Tianzhu Seismic Gap’ and nearby faults, raising seismic hazard in the region. These findings highlight the importance of simultaneously considering both afterslip and viscoelastic relaxation mechanisms in post-seismic deformation analysis, and accounting for post-seismic effects when evaluating seismic stress changes.