Postseismic Deformation Mechanisms of the 2021 Mw 7.4 Maduo Earthquake: Constrained from InSAR and GPS measurements

Summary Previous studies of the 2021 Mw 7.4 Maduo earthquake have primarily focused on the early postseismic phase, while the dominant mechanisms driving postseismic processes and the seismic moment released by afterslip remain debated. Longer-term observational constraints are needed to address these issues. In this study, we integrate ~3.5 years of postseismic InSAR and GPS time series data to effectively separate the contributions of afterslip and viscoelastic relaxation. The results show that afterslip released a cumulative seismic moment of approximately 3.91 × 1019 N·m, accounting for ~23.3 per cent of the coseismic moment—equivalent to a new Mw 7.0 earthquake. The optimal steady-state and transient viscosities of the lower crust are estimated to be 1.35 × 1019 Pa·s and 1.5 × 1018 Pa·s, respectively. Afterslip remains the dominant mechanism driving near-field deformation throughout the observation period, while viscoelastic relaxation governed far-field deformation beginning about 4 months after the mainshock. The stress-driven afterslip is comparable with the inverted kinematic afterslip, and poroelastic rebound is negligible. These findings provide valuable insights into stress perturbations on surrounding faults induced by the coseismic rupture, afterslip, and viscoelastic relaxation, and offer new constraints on the recurrence interval of Mw 7.4 earthquake on the Jiangcuo Fault.