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タイトル: Crusted Structure of a Seismic-Refraction Profile across the Median and Akaishi Tectonic Lines, Central Japan
その他のタイトル: 中部日本の中央構造線および赤右構造線を横切る屈折法測線の地殻構造
著者: Matsu'ura, Ritsuko S.
Yoshii, Toshikatsu
Moriya, Takeo
Miyamachi, Hiroki
Sasaki, Yoshimi
Ikami, Akira
Ishida, Mizuho
著者(別言語): 松浦, 律子
吉井, 敏尅
森谷, 武男
宮町, 宏樹
佐々木, 嘉三
伊神, 煇
石田, 瑞穂
発行日: 1991年12月27日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第66冊第3号, 1991.12.27, pp. 497-516
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.
URI: http://hdl.handle.net/2261/13090
ISSN: 00408972


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