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Abstract:
The Kanto earthquakes (M~8) recur along the Sagami trough, where the Philippine Sea plate subducts beneath the Kanto region. The most recent event was the 1923 earthquake which caused the worst earthquake disaster in Japan with ~105,000 casualties. The penultimate, 1703 Genroku earthquake caused larger crustal deformation and worse tsunami disasters in the southern Boso peninsula. Historical documents and tsunami deposits indicate that the 1293 Showo earthquake was also a Kanto earthquake. The 1495 Meio earthquake, considered to be confused with the 1498 earthquake along Nankai trough, may be another Kanto earthquake. Possibilities of the 878 and 1433 Kanto earthquakes have been also pointed out (Ishibashi, 2020, SRL). Marine terraces on the southern Boso peninsula indicate that the 1703 (Genroku) type earthquake recurred at approximately 2,300-year interval.
The Japanese government’s Earthquake Research Committee (ERC) annually estimates and announces long-term forecasts, in terms of occurrence probability in the next 30 years. For the M~8 Kanto earthquakes, the probability was estimated as 0 – 5 %, based on historical and geological data, while the Genroku type event was estimated as 0 %. The recurrence interval is calculated as 209 years for the above six historical events, 261 years for the five (excluding 1433) events, 210 years for the four (excl. 878 and 1433 or 1495) events, and 315 years for three (1923, 1703 and 1293) events. The 30-year probabilities vary 0 – 12 % for the Brownian Passage Time model, and 9 – 13 % for the Poisson model.
