A decadal-scale deformation transient prior to the 2011 Mw 9.0 Tohoku-oki earthquake

GPS time series in northeast Japan exhibit nonlinear trends from 1996 to 2011 before the M-w 9.0, 2011 Tohoku-oki earthquake. After removing reference frame noise, we model time series as linear trends plus constant acceleration, correcting for coseismic and postseismic effects from the numerous Mw similar to 6.5+ earthquakes during this period. We find spatially coherent and statistically significant accelerations throughout northern Honshu. Large areas of Japan outside the Tohoku region show insignificant accelerations, demonstrating that the observation is not due to network-wide artifacts. While the accelerations in northern Tohoku (Sanriku area) can be explained by decaying postseismic deformation from pre-1996 earthquakes, the accelerations in south-central Tohoku appear unrelated to postseismic effects. The latter accelerations are associated with a decrease in average trench-normal strain rate and can be explained by increasing slip rate on the Japan trench plate interface and/or updip migration of deep aseismic slip in the decades before the 2011 Tohoku-oki earthquake.