Lithospheric rheology in West Tibet and Pamir constrained from the postseismic deformation of the 2005 Mw7.6 Kashmir (Pakistan) earthquake

Abstract

We study the postseismic deformation of the 2005 Mw7.6 Kashmir earthquake in Pakistan, with a combination of the near- and far-field geodetic observations from the Kashmir Himalaya and the Tibetan Plateau, respectively. We construct a 3D finite-element model that integrates topographic relief, curved fault plane, and layered lithospheric structures to analyze stress-driven afterslip and estimate the rheological parameters of the Tibetan lithosphere. Our findings reveal that the ten-year afterslips of up to 30 cm were primarily localized at the downdip edges of co-seismic slip patches, causing near-field surface deformation of up to ∼5 cm within the first year. In contrast, viscoelastic relaxation in the lower crust of western Tibet and Pamir was required to reproduce far-field displacements of up to 1–2 cm recorded by GPS during the first 7 years. The model that best fits to the GPS displacements suggests a Maxwell viscosity exceeding 1020 Pa s for the Indian lower crust, while a much lower viscosity of ∼4–10×1018 Pa s is inferred for the lower crust beneath Pamir and western Tibet, indicating a softer Tibet and Pamir in response to the continental collision between India and Eurasia.