Triggering and Inhibition of Large Earthquakes in the Nankai Trough, Japan

University Of Memphis, Memphis TN

Investigators

Abstract

Abstract for proposal EAR-0003438 (PH #25x) PI: Paul Rydelek, University of Memphis Title: Triggering and Inhibition of Large Earthquakes in the Nankai Trough, Japan The Nankai Trough is formed by the subduction of the Philippine Sea Plate beneath southeast Japan. This thrust zone gives rise to great (M = 8) earthquakes every ~190 years, but the shortest repeat period in more than 1000 years was the 90 years after the 1854 Ansei earthquake. In addition, the 1944 Tonankai earthquake, possibly for the first time, did not extend northeastward into the Suruga Bay as previous great earthquakes in the Nankai Trough. Modeling shows that rather small stresses, when applied over the whole fault surface, are surprisingly effective in inhibiting or triggering large earthquakes in highly stressed regions. It is therefore suggestive that postseismic strain diffusion from the inland Nobi earthquake (M > 8) of 1891 may have affected the Coulomb failure level on the Tonankai fault consistent with the 1944 occurrence, i.e. the western section failed early but the eastern (Tokai) section did not fail. Using a computer simulation of the earthquake process, we propose to model the effect of small stress changes across a fault and investigate whether the level of stress due to strain diffusion from the great Nobi earthquake was indeed sufficient to trigger a 1944 size event. In addition, we plan to evaluate whether the inhibiting stress from Nobi earthquake, applied to the eastern part of the fault, is sufficient to temporarily delay the (Tokai) earthquake in excess of the historical repeat time. In more general terms, large earthquakes generate long-term and far-ranging stress perturbations that can influence the timing of large earthquakes on other faults. Therefore, the research proposed here is not strictly limited to large earthquakes in Japan, but rather anywhere.