Role of Poroelasticity and Viscoelasticity during the Postseismic Deformation of the 2021 M_w 7.4 Maduo, China, Earthquake

The 2021 M-w 7.4 Maduo earthquake within the Bayan Har block allows us to under-stand the lithospheric mechanical properties in northeastern Tibet. We analyze possible postseismic processes by modeling the six-month postseismic deformation from Interferometric Synthetic Aperture Radar data. Our optimal aftersli-poroviscoelastic model is not only physically more reasonable but also has the best data fit. The post -seismic deformation is dominated by afterslip located at depths of 10-20 km, revealing a complementary pattern with the up-dip high-coseismic slip. Yet ignoring poroelasticity and viscoelasticity will result in errors in afterslip of > 12 cm locally. Poroelastic rebound contributes to significant postseismic line of sight (LoS) deformation, up to similar to 14 mm, near the northwest and southeast fault segments. The steady-state viscosities in the lower crust and upper mantle are 4 x 10(19) Pa center dot s and 2 x 10(20) Pa center dot s, respectively, consistent with the "jelly sandwich" model but not with the crustal-flow models featuring much lower viscosity.