International Ocean Drilling Programme（IODP³）DV Chikyu to Set Sail for Expedition 502E/502/503

The Japan Agency for Marine-Earth Science and Technology (JAMSTEC: Hiroyuki YAMATO, President), will conduct three IODP³ Expeditions with the Deep-Sea Scientific Drilling Vessel Chikyu^*1 as part of the International Ocean Drilling Program (IODP³)^*2.

Appendix 1

International Ocean Drilling Programme (IODP³) DV Chikyu to Set Sail for Expedition 502E: Extended Monitoring and Resurveying of Japan Trench Borehole Observatories

1. Scientific background and objectives

IODP³ (Engineering) Expedition 502E aims to test key hypotheses about the long-term hydrogeologic and mechanical evolution of the Japan Trench megathrust by recovering and redeploying temperature sensor strings in observatory Holes C0019D and C0019Q and collecting data from the downhole formation.

Engineering expedition IODP³ Expedition 502E aims to test key hypotheses about the long-term hydrogeologic and mechanical evolution of the Japan Trench megathrust by redeploying temperature sensor strings in observatory Holes C0019D and C0019Q and conducting surveys of downhole deformation. Specifically, we hypothesize that permeability within the fault damage zone remains elevated relative to the plate boundary fault core and that hydrogeologic properties continue to evolve due to healing processes. Redeployed temperature sensors will allow us to assess changes over time by capturing thermal anomalies associated with fluid migration and hydrogeologic transients. We further hypothesize that horizontal fluid flow past the borehole varies with depth, reflecting structural heterogeneities within the fault zone. A Thermal Response Test will quantify background flow rates past the borehole casing, providing direct constraints on lateral fluid migration and its role in pressure redistribution. These data will be integrated with geochemical observations and temperature time-series analysis to assess the role of fluids in modulating fault strength.

2. Overview of the expedition

IODP³ Exp. 502E will recover and reinstall the long-term temperature observatories deployed in J-FAST Hole C0019D and JTRACK Hole C0019Q. First, 1) the drill string will re-engage the wellhead of Hole C0019D, and the retrieving tool will be passed through the string to recover the observatory. Next, 2) we will repeat this process at Hole C0019Q. Once onboard, the sensors will be refurbished, checked, data downloaded, and prepared for reinstallation. After that, 3) the drill string will be reconnected to the wellhead of Hole C0019D and the observatory will be redeployed, and 4) the observatory for Hole C0019Q will be redeployed in the same way.

3. IODP³ Expedition 502E Science Team

Co-Chiefs (3 people）

Patrick Fulton: Cornell University, USA^*
Jamie Kirkpatrick: University of Nevada, Reno, USA
Nur Schuba: The University of Texas at Austin, USA^*

*On-board co-Chief Scientists

In addition, 3 Science Communicators^*3 (1 from Japan) will participate. There will be no science team aboard the expedition, only a small team of engineers and lab technicians.

4. Expedition website

A dedicated website for the expedition has been launched. This website provides an overview of the expedition, introduces the participating researchers and will be updated with the progress of the expedition.
https:/www.jamstec.go.jp/chikyu/j/exp405/

Fig 1.　Survey Area. Recover and reinstall the Long-term temperature observatories deployed at Holes C0019 & C0019Q.

Fig 2. Drilling Plan

1. The drill string will re-engage the wellhead of Hole C0019D, and the retrieving tool will be passed through the string to recover the observatory.

2. Repeat this process at Hole C0019Q. Once onboard, the sensors will be refurbished, checked, data downloaded, and prepared for reinstallation.

3. The drill string will be reconnected to the wellhead of Hole C0019D and the observatory will be redeployed.

4. The observatory for Hole C0019Q will be redeployed in the same way.

Appendix 2

International Ocean Drilling Programme (IODP³) DV Chikyu to Set S ail for Expedition 502: Impact of Petit-Spot Magmatism on Subduction Zone Seismicity and Global Geochemical Cycles(T-Petit)

1. Scientific background and objectives

International Ocean Drilling Programme (IODP³) Expedition 502 plans to drill the outer rise area of the Japan Trench, where the sediment layer above the acoustic basement is unusually thin. There is a hypothesis that this thin sediment is caused by basalt intrusions or lava flows related to a type of volcanic activity called petit-spot magmatism. The goal of this expedition is to determine if this volcanic activity is more widespread than previously thought. If confirmed, it could significantly influence how subduction zones work, including earthquake processes, volcanic activity, and global chemical cycles. This research will help understand the role of petit-spot magmatism and its impact on the Earth’s systems.

2. Overview of the expedition

International Ocean Drilling Programme (IODP³) Expedition 502 plans to drill and the outer rise area of the Japan Trench, where the sediment layer above the acoustic basement is unusually thin.

3. IODP³ Expedition 502 Science Team

Co-Chiefs

Asuka Yamaguchi: The University of Tokyo, Japan
Hiroko Kitajima: Texas A&M University, USA

A total of 35 science team members will participate, including the two co-Chiefs, 24 onboard scientists (13 from Japan) and 9 research-only scientists (2 from Japan) selected from IODP³ participating countries. In addition, four science communicators will be on board.

4. Expedition website

A dedicated website for the expedition will be launched. This website provides an overview of the expedition, introduces the participating researchers and will be updated with the progress of the expedition.

Fig 3.　Survey Area. Drilling will be carried out at Proposed Site TPC-01A.

Fig 4. Drilling Plan

Three holes will be drilled at Proposed Site TPC-01A and the following operations will be carried out

1. Wireline logging
Drill 8-1/2 hole first and then run logging tool
target depth: ca. 230 m

2. Piston coring* (HCPS+ESCS) for shallow sediments
Coring Target depth: ca. 60 m

3. Rotary Coring* (SD-RCB) for igneous rocks
Coring Target depth: ca. 160 m
*The order of HPCS and SD-RCB will be decided by results from WL data.

Appendix 3

International Ocean Drilling Programme (IODP³) DV Chikyu to Set S ail for Expedition 503: Hadal Trench Tsunamigenic Slip History

1. Scientific background and objectives

International Ocean Drilling Programme (IODP³) Expedition 503 plans to drill a trench basin in the central Japan Trench to recover the whole trench-fill sequence for dating and establishing event-stratigraphy for paleoseismologic interpretations and further investigations of earthquake related element cycles in hadal trench environment. Combining stratigraphy and chronology of thick event deposits, interstitial-water geochemistry proxy-data for past fluid flow pulses and core-to-seismic correlation to paleo-slip-to-trench events, we would like to clarify how often the slip-to-trench events have occurred. Unravelling the complete trench-fill sedimentary record and pore water profile will significantly advance our understanding of the nature and recurrence of hadal trench tsunamigenic slip, the underlying megathrust earthquakes and related geohazards, as well as the effects on enhancing carbon accumulation in the hadal trench that may stimulate carbon transformation and eventual export into the subduction zone.

2. Overview of the expedition

IODP³ Expedition 503 consists of drilling and coring two adjacent 10-5/8 inch holes with the Hydraulic Piston Coring System (HPCS) to 160 meters below seafloor (mbsf) at Proposed Site JTC-1A to continuously recover the full trench-fill sequence. If HPCS refusal occurs before reaching the target depth of 160 mbsf in the first hole, extended shoe coring system and/or extended punch coring system (ESCS/EPCS) coring will continue to target depth or to refusal depth.

3. IODP³ Expedition 503 Science Team

Co-Chiefs

Ken Ikehara: National Institute of Advanced Industrial Science and Technology (AIST), Japan
Michael Strasser: University of Innsbruck, Austria

A total of 30 science team members will participate, including the two co-Chiefs, 25 onboard scientists (11 from Japan) and 3 research-only scientists (2 from Japan) selected from IODP³ participating countries. In addition, 5
4 science communicators (one from Japan) will be on board.

4. Expedition website

A dedicated website for the expedition will be launched. This website provides an overview of the expedition, introduces the participating researchers and will be updated with the progress of the expedition.

Fig 5.　Survey Area. Drilling will be carried out at Proposed Site JTC-01A.

Fig 6. Drilling Plan

Drilling and coring two adjacent 10-5/8 inch holes with the Hydraulic Piston Coring System (HPCS) to 160 meters below seafloor (mbsf) at Proposed Site JTC-1A to continuously recover the full trench-fill sequence.