反射法地震探査と重力測定による別府湾の地下構造

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書誌事項

タイトル別名
  • Subsurface Structure of Beppu Bay (Kyushu, Japan) by Seismic Reflection and Gravity Survey
  • ハンシャホウ ジシン タンサ ト ジュウリョク ソクテイ ニ ヨル ベップワン

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抄録

Multichannel seismic reflection profilings and gravity measurements give new information on the subsurface structure and the tectonic movement in the Beppu Bay area located at the northeast end of the Beppu-Shimabara Graben. Beppu Bay is structurally divided into the eastern and the western areas by a distinct tectonic line. In the eastern area, a graben structure whose axis runs parallel to the Median Tectonic Line is revealed by both the reflection profiles and the Bouguer gravity anomalies. The southern and the northern slopes of the graben are composed of the Sanbagawa Belt basement (SB) and the Ryoke Belt basement (RB), respectively. The surface of SB dips 30 degrees to the north at shallow depths and lowers at greater depths, and then SB lies below RB. The analysis of the seismic reflection and the gravity data suggests a possibility that an unknown formation having the similar density as SB may exist between SB and RB in the north part of this area. Many faults and folding structure in the thick sedimentary sequences overlying RB indicate that RB has been moved relatively to SB by dextral strike-slip movement, and has also slipped down along the surface of SB. On the other hand, the western area is subdivided into the main and the north parts. The main part is characterized by a basin structure buried by thick sediments, where an extremely low Bouguer gravity anomaly is observed. Active listric faulting is developed in the north part; the decolloment surface exists at about 300m depth below the sea floor.

収録刊行物

  • 地震　第２輯

    地震　第２輯 45 (2), 199-212, 1992

    公益社団法人 日本地震学会

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