Dynamic rupture scenarios of anticipated Nankai-Tonankai earthquakes, southwest Japan

Abstract

[1] We investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the Nankai-Tonankai subduction zone, southwest Japan. To improve the scenario reliability, the model parameters should be constrained by available data, or derived from their analysis. We employed the three-dimensional plate interface geometry and the slip-deficit rate on the interface. Accumulated slip-deficit was used to obtain the stress drop distribution of anticipated earthquakes. The estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes. Fault friction constitutive parameters, however, had to be assumed from indirect observations because they cannot be constrained directly by the data. Based on various geophysical observations, we defined three regions where larger fracture energy is required. These are the eastern edge of the Tonankai area, the western edge of the Nankai area, and the region between the Tonankai and Nankai areas (beneath the Kii peninsula). Such lateral heterogeneity promoted the segmented rupture along the Nankai trough. With predefined stress drop and constitutive parameters, various rupture scenarios for Tonankai and Nankai asperities were obtained for different initiation locations. In some cases, a single segment is ruptured, while in other cases, all the segments are broken due to dynamic linkage at the segment boundary, causing a giant earthquake. The initiation location is a critical parameter that controls the rupture propagation across the segment boundary. These scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest Japan.