Faculty of Science, Hokkaido University
Faculty of Education, Gifu University
School of Science, Nagoya University
National Research Institute for Earth Science and Disaster Prevention
抄録
In 1985, the Research Group for Explosion Seismology conducted a seismic refraction experiment along a profile in the central Japan region from Haruno, Shizuoka Prefecture to Tsukude, Aichi Prefecture. The 53km-long profile with six shot points and 76 temporary observation sites crosses two major tectonic lines: the Median and the Akaishi. The refraction analysis reveals the P-wave velocity structure down to 5km depth below the sea level under the profile. The structure of the upper crust along the profile is divided into four parts: A) the part east of the Akaishi tectonic line, B) the central part between two tectonic lines, C) the low-velocity zone at the Median tectonic line, and D) the part west of the Median tectonic line, by these two tectonic lines. The structure change at the Akaishi tectonic line is sharp, while the low-velocity zone of 4 km width exists under the Median tectonic line. P-wave velocities of the uppermost layers in A, B, C, and D are 3.1km/s, 4.4km/s, 3.8km/s, and 4.5km/s, respectively. The P-wave velocity of 6.0km/s appears at depths of 5.6km, 0.5km, 4.7km, and 2.6km below the sea level in A, B, C, and D, respectively. P-wave velocities in B are the highest at each depth. Those in D are the second highest, while those in A are the lowest. Although the profile is only 53km long, two velocity discontinuities are found in the deeper parts of this profile from reflected waves. One is at the depth of 14km under the Akaishi tectonic line. It extends 5km both to the east and west, and slopes down to the west at an angle of 22 degrees. This discontinuity corresponds to the upper boundary of the local high seismicity zone in the lower crust under the profile. The reflected waves at this discontinuity can be clearly recognized even in raw records, and a sharp velocity contrast of about 10% exists there. The other discontinuity lies about 10 km deeper beneath the former one, and slopes down to the west at an angle of about 10 degrees. This discontinuity can be recognized in a wider area under the profile. It corresponds to the upper surface of the Philippine Sea plate subducting toward the northwest in this area.
1985年11月,地震予知計画の一環として人工地震による地殻構造調査が,静岡県春野町と愛知県作手村を結ぶ全長約53kmの測線で行われた.この測線の位置は予想されている東海地震の震源域のすぐ西側であり,さらに,中央構造線と赤右横造線を横切っている.爆破点は測線上に6箇所,臨時観測点は76箇所である.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
66
号
3
ページ
497 - 516
発行年
1991-12-27
ISSN
00408972
書誌レコードID
AN00162258
フォーマット
application/pdf
日本十進分類法
453
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
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Crusted Structure of a Seismic-Refraction Profile across the Median and Akaishi Tectonic Lines, Central Japan
ji0663002.pdf
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