Triggering and inhibition of great Japanese earthquakes: the effect of Nobi 1891 on Tonankai 1944, Nankaido 1946 and Tokai

There are two unusual features of the most recent great earthquakes off southwest Honshu. The Tonankai and Nankaido earthquakes were relatively early compared to the historical record of past occurrence, and the Tokai section of the Tonankai fault did not fail in 1944 whereas it probably had for the previous ∼1000 years. We show that both phenomena can be explained by postseismic strain diffusion from the great Nobi, Japan, earthquake (M 8.0) in 1891. It is believed to have produced stress changes that influenced the time of occurrence of the great Tonankai (M 7.9) and Nankaido (M 8.0) earthquakes in the mid-1940’s. The pattern of long-term viscoelastic deformation following the Nobi earthquake suggests that the failure threshold was reduced in the southwest section of the Nankai Trough, which may have acted to trigger the Tonankai and Nankaido events. In contrast, the threshold was increased in the eastern Tokai section of the thrust zone and therefore failure of this section may have been inhibited. We model fault failure and show that the stress levels from Nobi are adequate to account for the advance of Tonankai and the inhibition of Tokai.