Coseismic deflection change of the vertical caused by the 2011 Tohoku-Oki earthquake (Mw 9.0)

SUMMARY This paper presents a scheme to compute coseismic deflection change, and presents a set of Green's functions for four independent dislocation sources. To compare the theoretical deflection changes with the GRACE-observed ones, the dislocation Love numbers are truncated and the Green's functions are computed with application of a Gaussian filter. Using this computing scheme, the modelled coseismic geoid and deflection changes can be compared directly with the GRACE-observed ones. Numerical computation and comparison show that the computing scheme is valid and efficient, and that it can obviate much unnecessary computing time for high-degree Love numbers. This study further examines the problem of sea water correction to modelled geoid and deflection changes because it is an important and necessary step to compare the modelled results with GRACE-observed deformations. As an application of the dislocation theory and the computing scheme described as a result of this study, we consider the 2011 Tohoku-Oki earthquake (Mw 9.0) using three different fault-slip models. Using the fault models, we compute the coseismic geoid and deflection changes for an area around Japan, considering sea water corrections. Results indicate that the coseismic geoid and deflection changes can be detected clearly by GRACE observation, and the coseismic geoid change is not sensitive to the fault-slip models: the three slip models yield identical coseismic geoid changes; whereas the coseismic deflection changes are very sensitive to the fault-slip models because the modelled deflection changes indicate pretty large difference, especially for the E–W component. These behaviours provide us a new and useful approach to invert seismic faults using GRACE-observed deflection changes as constraints.

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