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Stress perturbations and seismic response associated with the 2011 M9.0 Tohoku‐oki earthquake in and around the Tokai seismic gap, central Japan

The M9.0 Tohoku‐oki event is the largest earthquake in Japan's modern history. Social concerns and scientific interests require an urgent evaluation of this event's impact on other megathrust zones nearby Japan. Here we investigate the stress transfer from the Tohoku‐oki event on the Tokai subduction zone, where an M8‐class megathrust earthquake has been long‐time anticipated. First we demonstrate that the clear increase of crustal seismicity around Izu Peninsula, near the Tokai gap, is the consequence of a Coulomb static stress increase due to the Tohoku‐oki earthquake, calculated using a variable slip model for the mainshock and regional focal mechanisms of events occurred before and after the M9.0 earthquake. The largest stress increase is of about 1.0 bar, as estimated on earthquake nodal planes of maximum stress change. The time‐decay characteristics of the activated seismicity favor the triggering by static stresses. Such validations of the Coulomb hypothesis support our stress perturbation assessment on the Tokai gap. To precisely calculate the stress changes on the Tokai source, we use the curved plate interface and plate‐motion inferred rake directions. The computed stress changes are predominantly positive but have relatively small values, of less than 0.1 bar. The large afterslip (Mw8.6) and the aftershocks following the Tohoku‐oki earthquake caused additional, but minor, stress increases. Our results imply that the stress‐state on the Tokai plane did not change significantly after the Tohoku‐oki event, however static stress driven seismic activation in neighboring areas can bring a secondary impact on the interplate seismicity.