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

► The Stokes coefficients changes due to an arbitrary earthquake were derived. ► The polar motion excitation and low degree gravity changes were reformulated. ► The 2011 Tohoku-Oki earthquake changed J2 by less than 10−13. ► The 2011 Tohoku-Oki earthquake shifted the generalized figure axis by about 4 mas toward 132°E longitude.