著者

山中 浩明 瀬尾 和大 佐間野 隆憲 翠川 三郎 嶋 悦三 柳沢 馬住

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.41, no.4, pp.527-539, 1988-12-25 (Released:2010-03-11)

参考文献数

17

被引用文献数

6 6

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Seismic waves from explosions at nine sites were observed at a number of temporary stations in the southwestern Kanto plain. Travel time analyses were carried out along the several surveying lines, so that the contradiction at cross points of the lines becomes as small as possible. Underground structures along the surveying lines were studied to reveal the three dimensional features of the region. The results are summarized as follows:1) The structure consists of four layers which have P-wave velocities of 1.8, 2.8, 4.8 and 5.5km/s, respectively. Around the Yumenoshima explosion site, however, the thickness of the 4.8km/s layer seems to be very thin.2) The depth to the 4.8km/s layer becomes largest around Yokohama as more than 4km. The thickness of this layer is more than 3km in the central part of the area considered, such as Okazu and Hiratsuka. However, it becomes shallower near the Kurokawa and Higashi-ohgishima explosion sites.3) A step-like structure was found on the top of the 5.5km/s layer at points along the several surveying lines in the southeastern extension of the Tachikawa fault toward the Tokyo Bay area. On the southwestern side of the step-like structure, the depth to the 5.5km/s layer is more than several kilometers and this layer exists near the ground surface of the Kanto Mountains.

著者

山中 浩明 瀬尾 和大 佐間野 隆憲 翠川 三郎

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.39, no.4, pp.607-620, 1986-12-25 (Released:2010-03-11)

参考文献数

21

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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.

著者

山中 浩明 瀬尾 和大 佐間野 隆憲

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.44, no.1, pp.9-20, 1991-03-24 (Released:2010-03-11)

参考文献数

15

被引用文献数

1

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The seismic refraction survey was conducted in the southwestern part of the Tokyo Metropolitan area to make clear the deep sedimentary structure. Two explosions were made at Daikoku and Maioka in Yokohama city in 1988, and the resultant seismic waves were observed at 83 temporary observation sites along four surveying lines:a) Yumenoshima to Enoshima, b) Daikoku to Nagatsuta, c) Nagatsuta to Kanazawa, andd) around Takatsu.The travel time analysis for the above data and additional data from previous explosions in the area for reference has been made.The followings were our conclusions:1) The subsurface structure consists of five layers characterized by P-wave velocities of 1.8, 2.3, 2.9, 4.7 and 5.5km/s. The top layer with a P-wave velocity of 1.8km/s disappears around Enoshima. The layer with a P-wave velocity of 5.5km/s could not be confirmed for the southwestward area.2) The topography of the layer with a P-wave velocity of 4.7km/s forms a synclined structure having its maximum depth of more than 4km between the Maioka and Daikoku explosion sites. The depth to this layer becomes drastically shallower toward Enoshima.3) The step-like topography of the layer with a P-wave velocity of 5.5km/s, which has been found in the previous study, could not be confirmed, because of low S/N ratios of the observed seismograms.