Broadscale postseismic gravity change following the 2011 Tohoku-Oki earthquake and implication for deformation by viscoelastic relaxation and afterslip.

ABSTRACT: The analysis of GRACE gravity data revealed postseismic gravity increase by 6 ?Gal over a 500 km scale within a couple of years after the 2011 Tohoku-Oki earthquake, which is nearly 40-50% of the coseismic gravity change. It originates mostly from changes in the isotropic component corresponding to the M rr moment tensor element. The exponential decay with rapid change in a year and gradual change afterward is a characteristic temporal pattern. Both viscoelastic relaxation and afterslip models produce reasonable agreement with the GRACE free-air gravity observation, while their Bouguer gravity patterns and seafloor vertical deformations are distinctly different. The postseismic gravity variation is best modeled by the biviscous relaxation with a transient and steady state viscosity of 10(18) and 10(19)?Pa?s, respectively, for the asthenosphere. Our calculated higher-resolution viscoelastic relaxation model, underlying the partially ruptured elastic lithosphere, yields the localized postseismic subsidence above the hypocenter reported from the GPS-acoustic seafloor surveying.

SUBMITTER: Han SC 

PROVIDER: S-EPMC4373167 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature