Ocean science drilling explorations with D/V Chikyu: frontier and challenging

Abstract

Many international ocean science drilling programs (e.g. DSDP, ODP, IODP) have been conducted in the oceans all over the world for more than fifty years. A new phase of IODP (International Ocean Discovery Program) with three drilling platforms: the drilling vessel “JOIDES Resolution” by the US, the drilling vessel “Chikyu” by Japan, and the MSP (Mission specific platform) by Europe, began in 2013. Chikyu, operated by JAMSTEC since 2007, is the only riser drilling research vessel, which reaches to a total depth of 10,000m from sea surface. Our science approach to subsurface analyses is the integration of seismic surveys, well logging, core analysis, and long term observations. There are many successful projects achieved and on-going by D/V Chikyu. The purpose of NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment) is to understand earthquake mechanism in the Nankai trough, where the Pacific plate is subducting under Japan that has hosted historical large earthquakes and has potential for future earthquakes or tsunami. We surveyed many holes with well logging data and cores analysis. J-FAST is a project to study the faults, associated with the great earthquake in east Japan in 2011. The residual friction produced temperature anomaly was observed successfully with temperature array sensors in the borehole. The study of living organisms and their condition in the subsurface is important to understand the evolution of life on earth. The study off-shore Shimokita in 2013 clarified the limit of the micro-bios existence and the carbon cycle system subsurface there. Deep water hydrothermal deposits is a frontier for metal resources and active ore developemnt. We are developing unique approaches at the seafloor and subsurface with logging while drilling and coring in Okinawa. The challenges will be introduced with these targets, purpose, operations, and science achievements.