Deep-sea Scientific Drilling Vessel Chikyu to undertake three drilling expeditions for sample collection and other activities

The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has announced that it will conduct three expeditions using the Deep-sea Scientific Drilling Vessel Chikyu as part of the International Ocean Drilling Programme (IODP³).

IODP³ Expedition 502E "Extended Monitoring and Resurveying of Japan Trench Borehole Observatories" will be conducted approximately 200 kilometers off the coast of Miyagi Prefecture. During IODP Expedition 405 "Tracking Tsunamigenic Slip Across the Japan Trench (JTRACK)" conducted in 2024, long-term borehole temperature monitoring devices were successfully installed in drill holes (C0019D, C0019Q) around the fault zone in the Japan Trench. In this expedition, the devices will be recovered from the two drill holes, temperature data that has been continuously recorded since the JTRACK expedition will be retrieved, and then the devices will be redeployed in the same boreholes. Through analysis of the temperature monitoring data obtained and borehole surveys, the expedition aims to capture more detailed hydraulic structures around the fault zone along with temporal changes, and to clarify their relationship with seismic activity.

IODP³ Expedition 502 "Impact of Petit-Spot Magmatism on Subduction Zone Seismicity and the Global Geochemical Cycle" will investigate the outer rise of the Pacific Plate subducting into the Japan Trench, approximately 300 kilometers off the coast of Miyagi Prefecture. Previous surveys in this area of investigation have revealed that the sediment layers beneath the sea floor are extremely thin, with the influence of volcanic activity called "petit-spots" identified as a possible cause. Petit-spots are small-scale volcanic clusters characteristically distributed on the oceanward side of trenches, thought to erupt magma when the oceanic plate bends just before subduction. During the expedition, logging-while-drilling and core sample collection will be conducted to verify whether volcanic activity of petit-spots, estimated to exist beneath the seafloor at a water depth of approximately 5,400 meters, was more widespread than previously thought. The expedition further aims to clarify the role that petit-spots play in earthquake generation in subduction zones and in global material cycles.

IODP³ Expedition 503 "Hadal Trench Tsunamigenic Slip History" will collect core samples from the complete stratigraphic sequence of trench-fill sediments deposited in the central part of the Japan Trench, approximately 200 kilometers off the coast of Miyagi Prefecture. Using the core samples obtained, the expedition will conduct research with the following goals: to identify the ages of event deposits generated by shallow slip at the plate boundary and fluctuations accompanying great earthquakes using various methods, and to clarify their occurrence intervals and other aspects of past history; to analyze pore water contained in the sediments to determine its origin and evaluate the contribution of fluid presence to earthquakes or the impact of earthquakes on fluids; and to explore the effects of sediments transported to the trench during earthquakes on the deep biosphere and their relationship with material cycles.