title: 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 μGal 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 theMrrmoment 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 1018and 1019Pa 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.
authors.affiliation: Planetary Geodynamics Laboratory, NASA Goddard Space Flight Center Greenbelt, Maryland, USA.
authors.forename: Shin-Chan
authors.initials: SC
authors.lastname: Han
authors.affiliation: Planetary Geodynamics Laboratory, NASA Goddard Space Flight Center Greenbelt, Maryland, USA.
authors.forename: Jeanne
authors.initials: J
authors.lastname: Sauber
authors.affiliation: U.S. Geological Survey Menlo Park, California, USA.
authors.forename: Fred
authors.initials: F
authors.lastname: Pollitz
keywords: GPS; GRACE; afterslip; postseismic gravity; viscoelastic relaxation
references.citation: Science. 2011 Jun 17;332(6036):1395
references.pmid: 21596950
references.citation: Nature. 2011 Jun 15;475(7356):373-6
references.pmid: 21677648
references.citation: Science. 2006 Aug 4;313(5787):658-62
references.pmid: 16888136
references.citation: Science. 2011 Jun 17;332(6036):1421-5
references.pmid: 21596953
references.citation: Science. 2004 Jul 23;305(5683):503-5
references.pmid: 15273390
references.citation: Nature. 2012 Apr 18;484(7394):327-32
references.pmid: 22517160