The Integrated Ocean Drilling Program (IODP) is a large-scale international research program led equally by Japan and US. IFREE is proposing and conducting original and challenging research projects using the riser drilling vessel Chikyu that seek to comprehensively understand the Earth's evolution.
IFREE is preparing cutting-edge IODP drilling proposals, firstly one that seeks to drill into large igneous provinces (LIP) on the Earth's surface, and another that targets drilling across the Mohorovicic discontinuity, the boundary between the crust and mantle, and down into the mantle for the first time (the Mohole project). The former aims to understand the link between LIP activity and the evolution of the Earth system, while the latter will provide the first direct in situ samples of the Earth's mantle and Mohorovicic discontinuity.
IFREE has studied mechanism for large earthquake occurrence, crustal growth process, origin of life and nature of the mantle materials, which have been still unknown scientific targets yet. For understanding these issues, drilling studies through the IODP framework using D/V Chikyu is helpful. Before the drilling studies, seismic studies of crust and mantle are indispensable. These seismic studies, which measure seismic wave velocity distribution, contribute to reveal why and where large earthquakes occur and stop, or bring clues to understand histories for birth of life and crustal evolution. As seismic source, we use signals of high pressure air released from airguns in the sea. And the signals, which are returned from the crust and mantle, are recorded on a multichannel hydrophone streamer with dense pressure sensor array and ocean bottom seismographs with three component velocity sensors. Then, we obtain reflection image including faults/fractures images and construct a seismic model showing velocity distribution using these data. In this team, we will carry out seismic surveys for five years around the Nankai Trough and the Sagami Trough regions, the Izu-Ogasawara area, the Ontong java Plateau, and the northwestern Pacific.
IFREE have proposed to the IODP four sites in the Izu-Bonin-Mariana arc (IBM) for drilling with the riser drilling vessel Chikyu and with non-riser vessels. These proposals are currently being reviewed by the Science Planning Committee (SPC) and Science Steering and Evaluation Panel (SSEP) of IODP's Science Advisory Structure (SAS). If successful the results from the drilling will be integrated with ongoing sampling and seismic surveys using JAMSTEC vessels, remotely-operated vehicles (ROVs) and submersibles in the IBM. Together these all aid in understanding crustal formation and mantle evolution from the initiation of subduction, through the evolution of the oceanic arc, to the genesis of continental crust..