59.近年における日本の地震活動の二,三の特徴(1)

To study the process of occurrence of shallow earthquakes in and near Japan, the space and the time distributions of focal regions of large earthquakes and the earthquake energy density during the period (1885-1968, May) have been investigated. The results are summarized as follows: (1) During the last eighty years, earthquakes occurred with the space distribution showing a close relation to tectonic structures of this region. (2) Great earthquakes in this region occurred to fill gaps of seismic activity of thirty years and over, as pointed out in other circum-Pacific regions. It is particularly remarked that any large earthquakes of magnitude 7 and over did not occur in the focal regions of great earthquakes during the preceding period. (3) The seismic activity in the Kwanto and the southern Tohoku districts, including the part of the outer seismic zone, is abnormally low in the last thirty years. If the high activity in the preceding fifty years in this region is considered, this result suggests a possibility that great events may occur in the region in the near future.|日本及びその周辺の地震活動の空間的分布並びにその時間的変化を,マグニチュード7以上の大きい地震の震源域の分布及び小さい地震を含めた地震エネルギー密度の分布から論じた.できるだけ長期間についてしらべることがのぞましいが,この目的のための地震資料は,1885年以降に限られる.この最近約80年間についての調査の結果を次に要約す