Effects of nearby large earthquakes on the occurrence time of the Tokai earthquake—An estimation based on a 3-D simulation of plate subduction—

An eastern half of the focal region of the 1854 Ansei-Tokai earthquake was not ruptured at the 1944 Tonankai earthquake and the area around Suruga Bay remained as a seismic gap (Ishibashi, 1981). As to the cause that the fault motion in 1944 did not extend to the eastern part, Mogi (1981) and Pollitz and Sacks (1995) considered effects of the 1891 Nobi earthquake of M8.0. In this paper, we evaluate quantitatively effects of nearby large earthquakes, the 1891 Nobi, the 1923 Kanto and the 1944 Tonankai earthquakes, on the occurrence time of the Tokai earthquake that has been anticipated to occur soon to fill the seismic gap, using a three-dimensional simulation model with a rate- and state-dependent friction law (Ruina, 1983). It is suggested that the occurrence of the Tokai earthquake was delayed by the 1891 Nobi earthquake, while it was advanced by the 1923 Kanto and the 1944 Tonankai earthquakes. We show that the sense and degree of the effect of nearby large earthquakes on the occurrence time of the anticipated Tokai earthquake depend on whether and how much the stress perturbation produced by the nearby earthquakes strengthens or weakens the stress accumulated in the coupling region, especially in the highly shear-stressed ring zone (Kuroki et al., 2002). However it is difficult to say definitely how much the Tokai earthquake was delayed or advanced, because the magnitude of the effect is very sensitive to the location of the fault planes.