Tidal triggering of earthquakes prior to the 2011 Tohoku-Oki earthquake (Mw 9.1)

I observe highly significant tidal triggering of earthquakes prior to the 2011 M-w 9.1 Tohoku-Oki earthquake. Strong statistical correlations between tidally-induced stresses and earthquake occurrence times are identified in the northern part of the Tohoku-Oki source region, where the mainshock rupture initiated, in the several to ten years before the Tohoku-Oki earthquake. The tidal phase distribution of earthquakes in this period exhibits a peak where the shear stress is at its maximum to promote failure. On the other hand, no significant tidal correlation is found after the Tohoku-Oki mainshock. These observations suggest that tidal triggering occurs over a decade-long period preceding the Tohoku-Oki earthquake, and the initial rupture site of this event is already critically stressed in this precursory stage. Citation: Tanaka, S. (2012), Tidal triggering of earthquakes prior to the 2011 Tohoku-Oki earthquake (M-w 9.1), Geophys. Res. Lett., 39, L00G26, doi:10.1029/2012GL051179.