過去400年の日本の地震活動
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概要
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西暦1600年以降,我が国及びその周辺に発生した歴史地震データを用いて,嶋の震度の距離減衰実験式により,緯度,経度各1/2°ごとの格子点で経験されたであろう震度V,VIの回数を推定した.島崎・松田等の活断層分布と太平洋沿岸の過去の地震活動を考慮した地震危険度図と異なり,南関東が最も危険度が高いという結果が得られた.Seismic activity in Japan since 1600 is studied. The data source utilized is the list of historical earthquakes compiled by Usami. 409 earthquake data in total were available for this study. Using the empirical formula developed by Shima, the numbers of experienced intensities due to these earthquakes at mesh points 0.5 degrees apart were computed. It was found that, only a few places experienced ground motion stronger than Intensity VI twice during the past 400 years. Excluding part of Kyushu and Hokkaido, almost every site in Japan experienced ground motion stronger than Intensity V at least once. It was also found that southern Kanto is the most active region in Japan. The recurrence time of earthquakes in this region will be 25-50 years. SHIMAZAKI et al. proposed a seismic risk map of Japan utilizing the distribution of active faults. They claimed that the recurrence time of earthquakes expected in the mountaneous region of Chubu District will be less than 25 years. From our study, however, the seismicity of this region will not be that high, but as low as 1/3 of that of the southern Kanto region. This discrepancy may be due to their assumption of shorter recurrence interval of activation of the fault.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地震研究所の論文