Journal
GEOPHYSICAL RESEARCH LETTERS
Volume 41, Issue 16, Pages 5797-5805Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2014GL060905
Keywords
postseismic gravity; viscoelastic relaxation; afterslip; GRACE; GPS
Categories
Funding
- NASA's GRACE project
- Earth Surface and Interior program
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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)Pas, 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.
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