丸の内に於て觀測された地上及地下の地震動に就て

概要

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Lately the authors have observed seismic disturbances at Marunouchi where is the representative ground of the down town in Tokyo. These observations were held at the same time in three places; which are surface ground, 30 feet and 68 feet deep underground respectively. The 68 feet deep underground level is exactly the boundary of alluvium and diluvium. The diluvium is made of compact materials and its bearing power is greater than 20 tons per square foot, while the alluvium is made of soft materials and its bearing power is less than 1 tons per square foot. Therefore, these observations have determine how 68 feet thick soft alluvial layer vibrates by seismic disturbances. The instruments were Ishimoto's seismic accelerometers. The authors have found that, in alluvial layer, there are numerous waves having about 0.2 sec. and 0.7 sec. periods; in diluvial formation, 0.25 sec. and 0.45 sec. respectively. In consequence of drawing the resonance curve for vibrations in the alluvium, the author are able to ascertain that 0.25 sec and 0.75 sec. are the proper periods of the alluvial layer. More-over, the acceleration in 68 feet deep underground was about 1/3 to 1/5 of the surface ground. These data will be available to engineering seismology and prevention for earthquake disaster.
東京帝国大学地震研究所,Earthquake Research Institute, Tokyo Imperial University,地震研究所の論文
1934-09-30