| 講演要旨(和文) | | 本邦沿岸海域の海底地下構造を調査するため,新たに海底重力計を製作した.当該の海底重力計は,チタン合金製の球状耐圧容器内に収納された,ジンバルによる水平保持機能を施したシントレックス社製CG-5陸上用重力計からなるセンサー部とデータを収録するデータロガーから構成されている.重力の測定はオフラインで6Hzの周期で行われ,測定値はデータロガーに記録される.当該海底重力計の性能評価のため,その実海域試験を,2010年2月に神奈川県三浦半島金田湾で行った.重力測定を水深100m以浅の3箇所の海底で実施した.測定データについて,各種補正を行い相対重力値を計算し,絶対重力値既知点との閉合測定により,各測点での絶対重力値を求めた.絶対重力値に重力補正を行い,ブーゲー異常値を計算した.仮定密度2.3g/cm3のブーゲー異常値を既存の重力図と比較したところ,整合的な結果が得られ,当該装置の性能を検証できた. |
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| | 講演要旨(英文) | | A new ocean bottom gravimeter has been developed to better understand the subsurface structure of the transition zone of the Japanese coastal areas. The gravimeter consists of a Scintrex CG-5 gravimeter as a gravity sensor with free gimbals suspensions and a data logger within a pressure-resistant spherical container made from titanium. Observation data can be recorded to the data logger at a frequency of 6 Hz. A field experiment for the gravimeter was conducted in February 2010 in the Kaneda Bay of the Miura Peninsula. Gravity measurements were carried out at three gravity stations on the sea floor at depths from 20 to 40m below sea level. Tilt and temperature corrections were made for them after a conversion from raw data to relative gravity values from the base station at the port. The absolute observed gravity values were finally determined by tying to absolute gravity stations. Bouguer, terrain and other corrections were made by the gravity data processing procedure, SPECG1988. The density for both Bouguer and terrain corrections is taken to be 2.3 g/cm3. Bouguer anomalies at the gravity stations on the sea floor seem to conform in amplitude with regional gravity anomalies compiled mainly by shipborne gravity surveys. |
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