Recent scientific and operational achievements of D/V Chikyu

Abstract

The D/V Chikyu, a scientific drilling vessel, is equipped with industry-standard riser capabilities. Riser drilling technology enables remarkable drilling and downhole logging capabilities and provides unprecedented hole-stability, enabling the shipboard team to retrieve high-quality wire-line logging data as well as well-preserved core samples. The 11 March 2011 Tohoku Oki mega-earthquake and tsunami cost over 18,000 casualties in NE Japan. Chikyu, docked in the Port of Hachinohe, was damaged by the tsunami. By April 2012, the ship was back in operation; drilling the toe of the Japan Trench fault zone where topographic surveys suggested there was up to 50 m eastward motion, the largest earthquake rupture ever recorded. During Integrated Ocean Drilling Program (IODP) Expeditions 343 and 343 T, Chikyu drilled 850 m below sea floor (mbsf) in 6,900+ m water depth and recovered core samples of a highly brecciated shear zone composed of pelagic claystone. A subseafloor observatory looking for temperature signatures caused by the fault friction during the earthquake, was installed and later successfully recovered. The recovered temperature loggers recorded data from which the level of friction during the mega-earthquake slip could be determined. Following Exp. 343, Chikyu began IODP Exp. 337, a riser drilling expedition into the Shimokita coal beds off Hachinohe, to study the deep subsurface biosphere in sedimentary units including Paleogene-Neogene coal beds. New records in scientific ocean drilling were achieved in deepest penetration (drilling reached 2,466 mbsf) and sample recovery. Currently Chikyu is conducting deep riser drilling at the Nankai Trough in the final stage of the NanTroSEIZE campaign. During the years 2011 to 2013, including drilling in the Okinawa Hydrothermal System, Chikyu's operational and scientific achievements have demonstrated that the ship's capabilities are vital for opening new frontiers in earth and biological sciences.

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“…Life is found throughout the water column (the pelagic realm) and across the seabed (the benthic realm), down to the deepest ocean depths of nearly 11,000 m in the Challenger Deep, Marianas Trench (3). Microorganisms sustained through chemosynthesis have even been found as deep as >2,000 m below the seafloor (4). Despite the ubiquity of life, the deep sea may be viewed as an extreme environment, with an absence of sunlight below 1,000 m in depth, low temperatures (average <4 • C), and high pressures (average >400 atmospheres) (1).…”

IODP workshop: tracking the Tsunamigenic slips across and along the Japan Trench (JTRACK)

“…343/343T the D/V Chikyu penetrated and partially sampled the rupture zone of the 2011 earthquake (Chester et al, 2013a). Drilling in ultra-deep water depths of nearly 7 km, logging while drilling (LWD) data were collected, cores recovered from targeted intervals, and a borehole observatory for long-term monitoring of formation temperatures was installed (Chester et al, 2013a;Taira et al, 2014). LWD data and cores recovered from depths down to ∼ 840 m b.s.f.…”