POSSIBILITY OF A GREAT EARTHQUAKE IN THE TOKAI DISTRICT, CENTRAL JAPAN

Abstract

The Tokai district has been considered to be one of the probable sites of great interplate earthquakes in the near future. This idea is based on the time series of historical great earthquakes and the fairly high rate of crustal movement observed in this region for more than 80 years. The last great earthquake was the Ansei earthquake of 1854 (M=8.4). The western half of the source region of this earthquake ruptured again in the 1944 Tonankai earthquake, but the eastern half, i.e., the Tokai district, remain unruptured for 122 years. The recurrence time interval of great earthquakes in this region estimated from historical earthquakes, topographical and geological evidences, observed strain rates, the rate of plate convergence, etc. varies from 120 years to more than 600 years. There are several observations which may suggest that this region has already been in the long-term precursory stage. However, it is questionable that these observations represent real precursors to the future Tokai earthquake. It seems possible that the next great earthquake will occur south of the Izu Peninsula and will release the strain in the Tokai district. In any case, the Tokai district should be watched carefully for every conceivable precursors in order to make a successful prediction.