高知県室戸岬沖深海曳航調査速報(K96-03-MRT)

Abstract

A long-term deep seafloor observatory, seismometers and tsunami pressure sensors with a cable are to be deployed approximately 100 km off Muroto Peninsula in March 1997. Deep tow expedition (K96-03-MRT) was carried out for five days in April 1996 using R/V 'Kaiyo'. The purpose of the short cruise is to collect data to determine the cable route and sites for deploying the instruments such as seismometers, tsunami pressure sensors and a seafloor observatory. Seabeam box and route surveys were also carried out during the night time. In addition to the above surveys, the JAMSTEC (Japan Marine Science and Technology Center)/Digital OBS (Ocean Bottom Seismometer) and a mooring system were deployed for measuring seismicity and deep sea currents. A basic information on the topography to determine the cable route and sites for deploying the instruments was obtained during the Seabeam survey. Strong north-easterly Kuroshio currents were observed which ranged between 3 to 4 kts. Bottom currents on the landward slope of Nankai Trough were dominant toward the south which ranged between 5 and 35 cm/s. Unfortunately, the deep tow camera observation had to be postponed, expect in the shallow water which was less than 1,000 m, because of Tuna fishing in this area. The seafloor observatory will be deployed in Calyptogena Soyoae colony, which is common on the accretional wedge in Nankai Trough. Therefore, search for the clams is necessary and will be carried out in the next sea trial in 1996 by 'Shinkai 6500' and the JAMSTEC/Deep Tow.

高知県室戸岬沖に「海底地震総合観測システム」を構築するにあたって、1996年4月3日から4月11日にかけて高知県室戸岬沖深海曳航調査(K96-03-MRT)を実施した。「ケーブル型海底観測ステーション」のケーブル敷設予定ルートのシービーム地形調査を行うとともに、室戸市三津の高知県深層水研究所沖合で、4,000m級ディープ・トウカメラによる地形・地質などの調査を行った。先端観測点近傍の自然地震および深海の環境計測のため、先端観測点にデジタル地震計(OBS(海底地震計))1台と、流向流速計とCTD(伝導度-温度-深度プロファイラ)からなる係留系1基を設置し、先端観測点設置予定位置の周辺の自然地震観測および深海環境計測も併せて実施した。