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タイトル: 20. 昭和18年3月4日鳥取地震調査報告
その他のタイトル: 20. The Tottori Earthquake of March 4, 1943
著者: 表, 俊一郎
著者(別言語): Omote, Syun'itiro
発行日: 1944年8月15日
出版者: 東京帝国大学地震研究所
掲載誌情報: 東京帝国大学地震研究所彙報. 第21冊第3/4号, 1944.8.15, pp.435-457
抄録: A severe earthquake shook the neighbourhood of the City of Tottori at 19h 13m, March 4th, 1943. Shocks of the same magnitude occurred twice with an interval of ten houres. Seven houses were destroyed, ten persons wounded, but fortunately no life was lost. Arriving at Tottori two days after the earthquake, the writer immediately examined the damage caused and other phenomena that accompanied it, although, as a rule, such investigations made soon after the earthquake, do not always clear up at once the nature of the earthquake phenomena itself, rather it is some new data obtained from such detailed investigations when coordinated with data obtained from other past great earthquakes, that later throw light on problems concerned with the mechanism of the occurrence of earthquakes. The distributions of the damage are shown in Fig.1. The demolished houses were founed to lie in a belt-shaped. zone along the shore of the Sea of Japan, between Awoya and Uradome, and in the basin of the river Sendai. Roads and railways in those districts also suffered through banks, giving way. Damage was most marked in regions consisting of thick layer of sand, whereas on hilly ground the damage was inconspicuous. Answers to the question cards sent out into the affected districts by the Prefectural authorities at the request of the writer, were also the mean of considerable information. The questions asked were (1) the effects of the earthquake motion on pendulum clocks, (2) luminous phenomena and (3) sounds that accompanied the earthquakes, (4) earthfissures, (5) changes in the water of wells and hot springs. The answers received totalled 1300, forming the bases of our statistical investigations. The isoseismal lines of the percentage of stopped clocks (Fig.31) centered in , the sandy layered districts. Luminous phenomena : As already mentioned, shocks of nearly the same magnitude occurred twice at 19h 13m, March 4, and 4h 50m, March 5, a distance of 10km separating their respective epicenters. Accompanying both these shocks, luminous .phenomena were noticed by almost all who answered the post cards. In every case, the vectors of the directions in which the luminosities were seen converge to the respective epicentral regions(Figs.4, 5) with a probability of 10^<-10>. As pointed out by the late Or. T. Terada in discussing the cause of luminosities accompanying earthquake, care must be exercised to distinguish them from glares from houses on fire, lightning, electric sparkings, etc. In the case of the Tottori earthquakes no glows were seen after the. earthquakes. The weather on the night of the earthquakes was very calm and no thunderstom could be traced within range of possible suspition. As to electric sparking, the Tyngoku Haiden(electric power) Co. Ltd. informed us that the 3000kv high tension transm ission line broke down with the second earthquake(4h 50m, Mar. 5) while no short circuting took place with the first shock. Places where those breakings occurred, as will be seen from Fig.5, do not agree with the places to which the arrows converge. The Tottori district has no trolley car system. Our opinion is that the luminous phenomena observed on the occasions of the Tottori earthquakes are physically real, and that they are directly connected with the earthquakes. Earthquake sounds were also heard by a number of persons. The vectors of the directions in which they were heard converge to the epicentral region(Figs.6, 7). Numerous little fissurs were seen everywhere, but no fresh faulting movement extending to the surface has been observed anywhere on this occasion. The flow of many springs and wells were affected. In a number of the wells situated as much as 30km from the epicenter, the water for a time stood at higher levels than usual. In various places water was ejected from cracks formed by the shock. Detailed measurements of the directions of overturn of stone lanterns, agree with the directions from which the first shock came. The aftershocks were more numerous than is usual with shocks of the present severity. The number of shocks felt every three hours, after the main shock until March 22th may be seen from Fig.10. The "Pull-Push" distributions of the initial motions of the two earthquakes are shown in the maps, Fig.12, Fig.13. These two maps not only closely resemble each other, but also the pull-push distribution of the Hamamura earthquake that occurred on July 24th, 1935, strongly resembles the recent two. From these three maps, showing the pull-push distributions of the three earthquakes whose epicenters are so close to one another, the radius of the inflection circles may be taken as 210km±20km. With reasonable assumptions, we can determine the depth of the discontinuity in surface of the earth's crust to be 51km±3km.
URI: http://hdl.handle.net/2261/10604
ISSN: 00408972


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