Vol.6 No.3 2014

Research paper : Marine geological mapping project in the Okinawa area (K. ARAI et al.)−159−Synthesiology - English edition Vol.6 No.3 (2013) the Okinawan ocean region. The survey area of the Okinawa Project includes the Okinawa Trough, an active back-arc basin that contains the Tokara Islands and continuous submarine volcanoes that extend from Kyushu. The basin is renowned for volcanic and submarine hydrothermal activities.[3]-[5] We also discuss the current situation and recent issues facing AIST in the development of submarine mineral resources.2 Marine geological surveys, and organization and use of geological informationThe marine geology map series, published at the end of September 2012, includes 76 sheets based on marine geological surveys (Fig. 2), eight of which show the marine geology around Japan at a 1:1,000,000 scale. The more detailed 1:200,000 marine geology map series was also published, separated into sedimentological and geological maps, the latter of which include magnetic and gravity anomaly maps.To utilize the research vessel efficiently during AIST marine geological surveys, geophysical observations were primarily recorded during nighttime and sediment samples were taken from the stationary ship during the day (Fig. 3). In these surveys, the aim was to obtain ‘uniform data,’ defined as data that are systematically and comprehensively collected without any major variation in methods and equipment and of sufficient quality for geological interpretation. The sedimentological maps are based on seafloor surface samples collected using a grab sampler or columnar sampler, and they show the materials being deposited on the sea floor determined from sediment grain size and composition. The grab sampler was equipped with the conductivity depth profiler (CTD), turbidimeter, water sampler, and a submarine camera. Analyses conducted to produce these maps included sedimentology, geochemistry, and oceanography. The marine geological maps are based on seismic reflection profiling and the age of the sampled sediments. These maps display geological structure and stratification, and were created through integrated interpretations of structural geology, seismic stratigraphy, geophysics, sedimentology, etc.Figure 4 shows the scenario of the flow for basic geological information from data collection to data use. The various data collected during the offshore surveys are published as a database and marine geological maps, and are an important part of the available intellectual infrastructure. Figure 4 provides examples of potential uses for the data and maps, including assessments of geological hazards and submarine resource. The marine geological maps indicate, for example, the presence of faults and their activity, which may be used to assess geological hazards affecting oceanfront buildings. The sedimentological maps may be used for understanding the Fig. 1 Map of the sea floor geography around southwestern Japan showing major active hydrothermal areas and approved EEZ extension over the continental shelfThe black line shows the open sea and the green line shows the boundary with neighboring countries. The orange area marks the approved EEZ extension, and the yellow region indicates where the judgment has been postponed [Headquarters for Ocean Policy: Heisei 24 Nen Ban Kaiyo No Jokyo Oyobi Kaiyo Ni Kanshite Kojita Shisaku (2004 Situations of the Ocean and the Policies Taken for the Ocean)]. The Okinawa Trough is known for its active hydrothermal activities.[3]Ogasawara Plateau regionMinami-Io-jima regionSouthern Oki-Daito Ridge regionShikoku Basin regionOkinawa TroughActive hydrothermal region(Usui, 2010)Hydrothermal sulfide depositsManganese crust160°155°150°145°140°135°130°125°10°15°20°25°30°35°volcanic frontvolcanic front


page 26