シンポジウム
海底熱水鉱床を対象とした探査手法と統合解釈ツールの開発
2019 年 84 巻 1 号 p. 85-89
詳細
2019 年 84 巻 1 号 p. 85-89
In recent years, numerous geophysical survey method has been developed for exploring the marine resources in the EEZ （Exclusive Economic Zone） of Japan. Exploration targets have been gas hydrates, mineral resources （manganese nodule, cobalt rich crust or rare earth） and especially seafloor massive sulfide （SMS） deposits.
These resources exist in the shallow sub-seafloor in the deep sea （> about 1,000 m）. In seismic reflection survey, very high-resolution images are required but these cannot be effectively achieved by conventional techniques. In the “Nextgeneration technology for ocean resources exploration （Zipangu in the Ocean）” planned by the Strategic Innovation Promotion Program （SIP） launched by “the Council for Science, Technology, and Innovation （CSTI）”in Japan, scienti?c research on formation processes of ocean resources and technology development for ocean resource exploration are being carried out. As a part of this plan, we aimed to establish exploration methods for SMS deposits by a high-resolution seismic system.
In this program, which began in 2014, we developed acoustic survey methods specialized for different scales （from wide to detailed） and established a “Multi-Stage Explorations” for the SMS deposit. In the first wide area survey, we conducted two-dimensional acoustic survey using a deep-towed streamer cable（ ACS: Autonomous Cable Seismic）. As the second survey, we conducted detailed exploration for areas where detected seafloor hydrothermal activity. For acoustic survey in the hydrothermal activity area, complex seafloor topography such as chimney and mound must be considered.
Thus, we succeeded in separating structural re?ection and side reflections by towing vertically arranged hydrophone close the sea?oor （ZVCS: Zero-offset Vertical Cable Seismic） or mooring it on the sea?oor （VCS: Vertical Cable Seismic）.
In the final phase of this program, we proceeded with integrated interpretation of various geophysical data. For the interpretation of these data, it is important to apply knowledge of land ore deposits because of oceanic hydrothermal deposits are not fully understood. Therefore, we created a virtual space （DHF: Digital Hydrothermal Field） that can get into the outcrop of the deep sea by using the popular Virtual Reality （VR） technology.
