Stress transfer in the Tokai subduction zone from the 2009 Suruga Bay earthquake in Japan

Southwestern Japan lies at the boundary between the subducting Philippine Sea plate and the overriding Eurasian plate. A magnitude 8 megathrust earthquake ruptured the Tonankai and Nankai segments in 1944 and 1946, respectively, but the neighbouring Tokai segment of the plate boundary remained locked(1). A large megathrust earthquake in the Tokai region has therefore been expected. In 2009, a magnitude 6.4 earthquake took place in Suruga Bay, within the Philippine Sea subducting plate, close to the Tokai segment. Here, we use a fault-slip model to examine the impact of the stress changes(2) caused by the Suruga Bay event on the Tokai segment. We show that the occurrence rate of plate-boundary seismicity increased following the earthquake. Most of the presumed strongly locked patches of the Tokai segment are located within areas of increased stress. Rupturing of a locked patch-following a threshold level of seismic stress-could trigger the rupture of the entire Tokai segment, leading to a megathrust earthquake.