Topographic effects on coseismic gravity change for the 2011 Tohoku‐Oki earthquake and comparison with GRACE

Abstract

We estimate gravity changes due to coseismic horizontal deformation and inclined bathymetry (referred to as topographic effects in this study) associated with the 2011 Tohoku‐Oki earthquake, using a layered half‐space dislocation model. As an approximation, we represent inclined topography with ramp‐body models in the near field of the earthquake and calculate topographic effects from both an inclined seafloor and Moho. The Moho effect partly compensates that from the seafloor. An additional contribution comes from seawater column variations as the sloped seafloor moves trenchward. Topographic effects are first‐order contributions to coseismic gravity changes for the 2011 Tohoku‐Oki earthquake. After 300 km Gaussian smoothing, comparable to the spatial resolution of the Gravity Recovery and Climate Experiment (GRACE), topographic effects create a dominantly negative gravity pattern with amplitudes up to 1.1 μGal for oceanic areas surrounding the epicenter. There are discrepancies between model predictions (−10.4 to +6.9 μGal) and GRACE observations (10.1 to +1.7 μGal). Errors in the adopted fault slip model and difficulties in separating coseismic and postseismic deformation may contribute to these, but topographic effects, currently neglected in dislocation models, are also responsible. Topographic effects ought to be included in coseismic fault slip and related gravity modeling for the 2011 Tohoku‐Oki earthquake and similar events in regions of steep topography.

Evaluation of GRACE/GRACE Follow-On Time-Variable Gravity Field Models for Earthquake Detection above Mw8.0s in Spectral Domain

“…Figure 9b shows the time series of selected points near Japan with peak-to-peak a range of −1.3~0.2 µGal. According to the residual RMS distribution, the hydrological signal level is around 0.4 µGal, which is consistent with Li et al [42]. Figure 9c,d shows the time series of selected points and RMS variations in Chile and Peru, with the amplitude in the range of −2.6~+3.6 and −8.1~+3.5 µGal, respectively, in which the amplitude variation of the hydrological signal is generally larger than those of Sumatra and Japan.…”

Gravity and geoid changes by the 2004 and 2012 Sumatra earthquakes from satellite gravimetry and ocean altimetry

“…Also, horizontal movements of slant surfaces bring similar effects to the surfaces elevations ( Fig. 1c), which, however, are often relatively small (Li et al 2016). Secondly, post-seismic gravity changes are supposed to result from the afterslip, visco-elastic relaxation, and poro-elastic rebound of the upper mantle.…”

Seismic Impact of Large Earthquakes on Estimating Global Mean Ocean Mass Change from GRACE

“…For example, de Linage et al [35] shows that with a non-linear optimization method, the range of the estimated post-seismic parameter τ for the December 2004 Mw9.1 earthquake is 0.5-0.75 year (i.e., 6-9 months) in the region surrounding the epicenter. Li et al [42] applies a residual minimization standard of the observations and indicates that the value of post-seismic parameter τ for the March 2011 Mw9.0 Tohoku-Oki earthquake is around 0.32 year (i.e., 4 months). Therefore, in this study we used τ = 7 and τ = 4 months to fit the post-seismic terms for the Sumatra and Tohoku-Oki earthquake regions, respectively.…”