Reformulation of co-seismic polar motion excitation and low degree gravity changes: Applied to the 2011 Tohoku-Oki earthquake (Mw9.0)

Abstract

New formulas for computing coseismic polar motion excitation and low-degree gravity changes, not only for shear but also for tensile earthquake, based on point dislocation theory are presented, with a set of concise expressions of Stokes coefficients in terms of dislocation Love numbers and fault parameters. The formulas directly involve an arbitrary seismic source and coseismic deformation and are validated through numerical computation for some specific earthquakes by comparison with previous results obtained using a normal mode approach. As an application, the formulas are applied to compute coseismic polar motion excitation and low-degree gravity changes caused by the 2011 Tohoku-Oki earthquake (Mw9.0). Numerical results show that the coseismic J2 change reaches magnitudes of between 10−14 and 10−13, and coseismic J3, J4, and J5 changes appear at a magnitude of 10−12. Furthermore, the polar motion excitation and J3 and J4 changes are explicitly dependent on the slip magnitude of the sub-fault whereas J2 and J5 are explicitly dependent on the horizontal location of the sub-fault. In addition, the generalized figure axis should have shifted by about 4mas (milliarcseconds) toward 132°E longitude.