Abstract
Several recent large-scale earthquakes including the 2011 Tohoku earthquake (M w 9.0) in northeastern Japan and the 2014 Iquique earthquake (M w 8.1) in northern Chile were associated with foreshock activities (M w > 6). The detailed mechanisms between these large earthquakes and the preceding smaller earthquakes are still unknown; however, to plan for disaster mitigation against the anticipated great Nankai Trough earthquakes, in this study, possible scenarios after M w 7-class earthquakes that frequently occur near the focal region of the Nankai Trough are examined through quasi-dynamic modeling of seismic cycles. By assuming that simulated Nankai Trough earthquakes recur as two alternative earthquakes with variations in magnitudes (M w 8.7–8.4) and recurrence intervals (178–143 years), we systematically examine the effect of the occurrence timing of the M w 7 Hyuga-nada earthquake on the western extension of the source region of Nankai Trough earthquakes on the assumed Nankai Trough seismic cycles. We find that in the latter half of a seismic cycle preceding a large Nankai Trough earthquake, an immature Nankai earthquake tends to be triggered within several years after the occurrence of a Hyuga-nada earthquake, then Tokai (Tonankai) earthquakes occur with maximum time lags of several years. The combined magnitudes of the triggered Nankai and subsequent Tokai (Tonankai) earthquakes become gradually larger with later occurrence of the Hyuga-nada earthquake, while the rupture timings between the Nankai and Tokai (Tonankai) earthquakes become smaller. The triggered occurrence of an immature Nankai Trough earthquake could delay the expected larger Nankai Trough earthquake to the next seismic cycle. Our results indicate that triggering can explain the variety and complexity of historical Nankai Trough earthquakes. Moreover, for the next anticipated event, countermeasures should include the possibility of a triggered occurrence of a Nankai Trough earthquake by an M w 7 Hyuga-nada earthquake.
Highlights
It is well known from historical seismology that Mw 8 earthquakes have been recurring at the Nankai Trough since 684 CE, causing severe damage to the Japanese Islands
If an Mw 7 Hyuga-nada earthquake does not occur in the several decades, no matter where the Nankai earthquake is initiated, the Nankai Trough earthquake may be a short time interval rupture type of Mw > 8.5, as shown in Figs. 9c and 10c for 80–100 %
Concluding remarks To explore possible scenarios for the Nankai Trough earthquake, we focused on Nankai earthquakes triggered by a preceding Hyuga-nada earthquake and investigated the conditions in which such triggering occurs
Summary
It is well known from historical seismology that Mw 8 earthquakes have been recurring at the Nankai Trough since 684 CE, causing severe damage to the Japanese Islands. Approximately nine successive Nankai Trough earthquakes (in 1946 and 1944, 1854, 1707, 1605, 1498, 1361, 1099 and 1096, 887, and 684) have been documented in the historical record over. Hyodo et al Earth, Planets and Space (2016) 68:6 Kyoto Kyushu Bungo. Cape Ashizuri channel Hyuga nada Z Shikoku Kochi Cape Muroto
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