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タイトル: 30. Aftershocks of Imaichi Earthquake Observed at Nishi-oashi Station
その他のタイトル: 30. 西大芦村で觀測されたこ今市地震の余震
著者: Omote, Syun'itiro
著者(別言語): 表, 俊一郎
発行日: 1951年3月25日
出版者: 東京大学地震研究所
掲載誌情報: 東京大學地震研究所彙報. 第28冊第3/4号, 1951.3.25, pp.401-413
抄録: In concluding these reports, the results obtained will be summarized as follows:- (1) Some 95 foci of Imaichi aftershocks. were located by the data obtained at the single station, Nishi-oashi, which had three components of seismographs at its desposal. (2) Epicenters of these aftershocks were mainly concentrated in the area bounded by a triangle whose apices were Nishi-oashi, Imaichi and Nikko, and this fact was in good accord with the result obtained by the difference time method. (3) Occurrence of shocks, though small in number, in the northwest and southwest quadrants was confirmed. (4) The incident angle of the first P wave was calculated. In this, as the vertical motion seismometer had the free oscillation period of 0.1sec., Tsuboi's method was made use of for the purpose of determining the true initial amplitude of the vertical component. (5) The majority of shocks had incident angles of about 10°~30° and the assumption of the existence of a discontinuity surface with a slightly bigger velocity within the earth was found to provide favourable explanation to it. The depth of this discontinuity will not be greater than 2.5km. (6) With respect to these shocks with small incident angles the depth of foci and the epicentral distance were calculated. (7) Some observations were made regarding the distribution of the first impulsions of aftershocks. In conclusion the author wishes to express his hearty thanks to Professor T. Hagiwara for his valuable advices. A part of the expense of this study was defrayed from the Scientific Research Fund of the Department of Education.
URI: http://hdl.handle.net/2261/10739
ISSN: 00408972


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