New marine seismic survey techniques for seafloor massive sulphide (SMS) exploration

Within the EEZ of Japan, numerous surveys exploring ocean floor resources have been conducted. The exploration targets have been gas hydrates, mineral resources (manganese cobalt rich crust or rare earth) and especially seafloor massive sulphide (SMS) deposits. These resources exist in shallow subsurface areas in deep waters (>1000m). For seismic explorations very high resolution images are required but these cannot be effectively achieved by the conventional marine seismic techniques. We have been developing new marine seismic survey systems which can acquire the data close to the seafloor in order to preserve high frequencies. One is vertical cable seismic (VCS) systems and the other is deep-tow seismic system. With both systems, seismic data is continuously recorded in the vicinity of ocean floor. Highly accurate clock is necessary for the synchronization of the data recoding with high sampling rate of 10 kHz in the water. We already have carried out more than 10 VCS surveys in actual hydrothermal area and it gave us high quality results. It is ready for the practical use. We modified the VCS system to use as a more efficient deeptow seismic survey system. Although there are other examples of deep-tow seismic systems, signal transmission cables present challenges in deep waters. We use our autonomous recording system to avoid these problems. Although the data cannot be monitored in real-time, the towing system becomes very simple. We are carrying out test surveys, which show the systems utility as a high-resolution deep-tow, near ocean bottom, survey system. It is still in the experimental stage. These systems will continue to be developed as part of the governmental project of SMS exploration by combining other geophysical, geological and mineralogical exploration methods.