- 公益社団法人 日本地震学会
- 地震 第2輯 (ISSN:00371114)
- vol.39, no.4, pp.607-620, 1986-12-25 (Released:2010-03-11)
The seismic refraction prospecting was carried out in the southwestern part of the Tokyo Metropolitan area, to clarify the deep underground structure down to uppermost layer of the Earth's crust. The explosions were denoted at Nagatsuta, Kurokawa, Okazu and Yumenoshima. The explosion at Nagatsuta was planned to make clear the existence of vertical discontinuity of the basement between Nagatsuta and Yumenoshima, which has been suggested from the observation of Yumenoshima explosion. The underground structure was revealed by the travel time analysis. The main features of the underground structure are as follows:1) The underground structure consists of 4 layers. The P wave velocities of these layers are 1.8 to 2.0, 2.9, 4.8 and 5.5km/s, respectively.2) The thickness of the third leyer is several kilometers in this area, however this layer doesn't exist in the central part of the Kanto plain.3) The first layer is thinner than the second one in contrast with the underground structure of Yumenoshima situated on the center of the Kanto plain.4) The vertical discontinuity of the basement was not confirmed from Nagatsuta explosion, because the refracted wave from the basement was not observed as an initial motion at the expected stations.