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タイトル: 4. 昭和19年12月7日東南海大地震に伴つた津浪
その他のタイトル: 4. The Tunami, the Earthquake Sea Waves, that Accompanied the Great Earthquake of Dec. 7, 1944
著者: 表, 俊一郎
著者(別言語): Omote, Syun'itiro
発行日: 1948年6月30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24冊第1/4号, 1948.6.30, pp.31-57
抄録: 1). A great earthquake took place on December 7, 1944, the epicenter of which was announced by the Central Meteorological Observatory to be at λ=143°E, φ=34°N, in the Kumano-nada, a long way off the coast of Mie Prefecture. With this earthquake a violent tunami or earthquake sea wave was generated, and its effect was noticed in unusually high tides that occurred as far as Simoda harbour in the east and thd cape of Siwonomisaki in the west. General idea of the heights of water at the occurrence of the tunami will be obtained from Fig.1, in which it is apparent that, along the coasts of the Ise and the Atumi Bays that do not directly face the open sea, the heights of the tunami water amounted to only two meters or so. Along the coast of the Sea of Ensyu-nada too, the heights were quite insignificant, owing to the monotonous contour of the coast. Along the coast of Sima and Kii Peninsulas, on the other hand, the tunami swept with the heights of over eight ,meters, causing extensive damages to the coastal regions. The coast of these districts is highly indented, forming a typical topography of the Rias coast, and it can safely be said that the unusual heights of the tunami waves along this coast were largely due to this circumstance. The details of the height of the tunami waters with respect to the individual villages inspected by the author are shown in Figs.2-5. As we see in these figures, in such bays as Owase, Atasika, Nisiki and Yosizu that are open to the outer ocean, the tunami water rose to an enormous height. Especially the damages done to the villages on Nisiki and Yosizu Bays were such that almost 90% of their dwelling houses had been swept away. 2). The disturbance of the sea-waters caused by the tunami left goot records at various mareograph stations. Such records collected by the author are reproduced in Fig.11. Among these mareograms, those four that were obtained by the stations that happened to be near the epicenter recorded clear by the beginning of the tunami as well as the disturbance of waters due to the earthquake motions. So it was easy to know from these mareograms the length of time that had elapsed between the occurrence of the earthquake and the arrival of the tunami at the station.Moreover, even in some stations where mareographs had not been installed, thanks to the watchfulness of the observers, this lapse of time had been measured. From the mareographic records or from the data offered by the wa chful observers we were able to know the time needed by tunami waves to reach the places denoted A, B, …, F in Fig.10. Then, taking each station as an imaginary wave-source, and imagining that the tunami waves start from this point into the offing, we obtain a curve representing the imaginary wavefront after the la se of time that is equal to the observed travel time needed by the actual waves to reach each station. These curves are shown by small curves denoted as A, B, …c, F in Fig.10. The enveloping circle to these curves is shown by a dotted line in Fig.10, and has a diameter of about 300km. It will be a problem for further discussion whether or not the area that is enclosed by the dotted line would represent the true boundary of the origin of the disturbance from which the tunami started. If we take the velocity V of the tunami to be V=√<gh>, where is the depth of the ocean and has the value of s me, 3000 meters, the wave length of the tunami wave having the period of 30 minutes will be calculated at 300km, which is of nearly the same value as the linear dimension of the area of the source of the tunami.
URI: http://hdl.handle.net/2261/10630
ISSN: 00408972
出現カテゴリ:東京大学地震研究所彙報
東京大学地震研究所彙報

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