==================================== CHIKYU MAIL NEWS Vol. 75, November 16th 2007 This mail news service provides you with information about the Deep Sea Drilling Vessel "Chikyu" and science and technology for the IODP Earth exploration. CHIKYU HAKKEN WEB SITE http://www.jamstec.go.jp/chikyu/ ==================================== ------------------------------------------------------------------- [JAMSTEC Press Release] November 16, 2007 Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Deep-Sea Drilling Vessel Chikyu Successfully Completes Expedition 314 http://www.jamstec.go.jp/e/about/press_release/20071116/ ------------------------------------------------------------------- 1. Outline The Japan Agency for Marine-Earth Science and Technology (JAMSTEC; Mr. Yasuhiro Kato, President) is pleased to announce that the Deep-sea Drilling Vessel Chikyu has just completed the first IODP*1 expedition, "Expedition 314" of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) as of November 15th. 2. Expedition 314 overview Chikyu has spent 56 days carrying out scientific drilling in the Kumano basin off the Kii peninsula from September 21st to November 15th. The primary goals of Expedition 314 are to obtain a comprehensive suite of geophysical logs and other downhole measurements at six sites across the Nankai accretionary complex using the most sophisticated logging while drilling (LWD)*2 technology. Dr. Masataka Kinoshita (Group Leader of Deep Sea Research Group, Institute for Research on Earth Evolution, JAMSTEC) and Dr. Harold Tobin (Associate Professor, Department of Geology and Geophysics, University of Wisconsin-Madison, USA) are the Co-Chief Scientists, while the science party comprises 16 onboard scientists from 6 countries. 3. Primary results Twelve boreholes were drilled at six sites. LWD drilling was conducted at five sites in the Nankai Trough accretionary complex off Kumano. Drilling conditions were severe at three sites due to strong deformation within the accretionary prism, caused by plate conversion and possibly by interseismic stress accumulation. Furthermore, operations were conducted within the strong Kuroshio Current, which was often stronger than 4 knots. However, with the drilling capability of Chikyu we successfully completed drilling down to 400 m to 1400 m below the seafloor and obtained high quality in-situ physical properties as well as borehole images. (For details, please refer to appendix.) Images of the borehole walls using electrical resistivity allow us to deduce the stress conditions at each drill site. We found that the stress condition and geologic structure of the uppermost 1-1.5km of accretionary prism is very different above seismogenic zone, between the thrust sheet above the mega-splay (Sites C0001 and C0004) and landward side of the Kumano forearc basin (Site C0002). These data are useful to infer the formation process of the accretionary prism and seismogenic mechanisms in the Kumano basin. At Site C0002, we identified a methane hydrate-rich zone at 220 to 400 m below the sea floor based on high resistivity image and low gamma ray data. Hydrates are concentrated in sandy layers of numerous turbidites in this zone. 4. Following expeditions The next NanTroSEIZE Expedition 315 has immediately begun since November 16th. This expedition will revisit one of the sites (C0001) drilled during Exp314 and take continuous samples from the upper section of active accretionary prism sediment down to 1000m below the sea floor. It also serves as a pilot hole for the riser drilling to the Megasplay fault scheduled for next year. Contacts: (For Chikyu) Mr. Takeo Tanaka, e-mail: cdex@jamstec.go.jp Manager, Planning and Coordination Department The Center for Deep Earth Exploration (CDEX) Japan Agency for Marine-Earth Science and Technology (For Research) Dr. Harold Tobin, e-mail: htobin@wisc.edu Co-Chief Scientist of Expedition 314 Associate Professor, Department of Geology and Geophysics University of Wisconsin-Madison, USA Dr. Masataka Kinoshita, e-mail: masa@jamstec.go.jp Co-Chief Scientist of Expedition 314 Group Leader of Ocean Bottom Observation Research Group Institute for Research on Earth Evolution Japan Agency for Marine-Earth Science and Technology (For Publication) Mr. Shinji Oshima, e-mail: press@jamstec.go.jp Manager, Planning Department Press Office Japan Agency for Marine-Earth Science and Technology *1: Integrated Ocean Drilling Program (IODP) The Integrated Ocean Drilling Program (IODP) is an international marine research drilling program dedicated to advancing scientific understanding of Earth by monitoring and sampling subseafloor environments. Through multiple platforms, preeminent scientists explore IODP principal themes: the deep biosphere, environmental change, and solid earth cycles. IODP has been operating since October 2003, led by Japan and the USA. IODP now has 21 member countries. *2: Logging While Drilling (LWD) LWD is a technique to measure geological formation properties at a site while drilling, by attaching a physical measurement sensor near the drill bit. Through continuous in-situ monitoring during drilling, geological data can be obtained quickly. It is necessary for drilling into complex geological structures, especially in the Nankai Trough, to acquire scientific geological data, and for the following coring operation, to have data on borehole conditions for safety monitoring and risk mitigation. Data expected to be obtained by LWD are formation density, porosity, velocity of sound speed, natural gamma ray and resistivity. *3: Nankai Trough Accretionary Prism The Nankai Trough in Suruga Bay runs to off the coast of Tokai, the Kii Peninsula, Shikoku, and Kyushu, where the Philippine Sea Plate subducts under the west-south Japanese archipelago (Usually, "trough" indicates a long thin ditch on the sea-floor, but here means "trench", one is approximately 770 km long). Along with this plate subduction, sediment on the plate is being scraped off and added to the continental plate, with such newly-formed geological sediments called "accretionary prism". It's development and history are very important in understanding the basic process of orogenesis, and front-line research is being conducted in the seismogenesis zone. ----- Appendix ----- Table-1: Drilling data Table-2: Summary of drilling result Site Name: C0001, Proposed Site: NT2-03 Latitude: 33.14.3N, Longitude: 136.42.7E Water Depth: 2,180m Drilling Depth (below the seafloor): Pilot Hole (1,000.0m), GeoTech Hole (30.5m), LWD Hole (77.5m and 976.0m) Drilled into a thrust sheet in hanging wall of the mega-splay fault system. Logged and imaged deformed accretionary prism rocks and collected data on stresses in prism system. Piloted the planned first riser drilling site. (*GeoTech Hole: Collect core samples to evaluate soil density for upcoming riser drilling.) Site Name: C0002, Proposed Site: NT3-01 Latitude: 33.18.0N, Longitude: 136.38.2E Water Depth: 1,970m Drilling Depth (below the seafloor): LWD Hole (1,401.5m) Succeeded to drill the deepest hole into an accretionary prism both in scientific and LWD drilling history. Imaged and logged data clearly identified basal layer of Methane hydrate at 400 meters below the seafloor (mbsf) and boundary between basin sediment and underlying accretionary prism. Piloted the 2nd planned riser drilling site to be attempted to 6,000 mbsf. Site Name: C0003, Proposed Site: NT2-01D Latitude: 33.13.4N, Longitude: 136.42.1E Water Depth: 2,453m Drilling Depth (below the seafloor): LWD Hole (530.0m) The original plan was to penetrate the splay fault zone at 710 mbsf. However, the drilling was aborted at 530 mbsf where the lower part of drill pipe disconnected because of excessive pressure and torque inside of the borehole. Abandoned retrieval (released on October 29, 2007). However the recovered data such as density, resistivity and gamma-ray intensity are valuable to characterize properties in active accretionary prism. Site Name: C0004, Proposed Site: NT2-01I Latitude: 33.13.2N, Longitude: 136.43.2E Water Depth: 2,524m Drilling Depth (below the seafloor): Pilot Hole (400.0m), LWD Hole (400.0m) Drilled through the splay fault at 300 meters below the seafloor. A pilot drilling was made first and confirmed the drillability with LWD. High quality images and log data were acquired. The splay fault zone anticipated at approximately 300 mbsf was very well-imaged and logging data detected fault properties. For the first time drilling through the mega-splay fault was made successful. Site Name: C0005, Proposed Site: NT2-01E Latitude: 33.13.6N, Longitude: 136.43.1E Water Depth: 2,446m Drilling Depth (below the seafloor): Pilot Hole (524.0m) Planned to drill and log into the splay fault. A pilot drilling was made first to confirm drillability with LWD. Drilling became difficult at 524 mbsf and after attempted to remedy borehole status, abandoned because of the excessive risk. Site Name: C0005, Proposed Site: NT2-01G Latitude: 33.13.4N, Longitude: 136.43.2E Water Depth: 2,454m Drilling Depth (below the seafloor): Pilot Hole (37.0m) Planned to drill and log into the splay fault. Determined to abandon drilling because of limited time remaining in the expedition. Site Name: C0006, Proposed Site: NT1-03 Latitude: 33.01.6N, Longitude: 136.47.6E Water Depth: 3,830m Drilling Depth (below the seafloor): Pilot Hole (885.5m), LWD Hole (885.5m) Drilled the point of 1 km landward from the toe of the accretionary prism. A pilot drilling was made to confirm drillability for LWD. Drilled through early formation stage layer of the accretionary prism, including the frontal fault zone, and reached 885 mbsf. # ------------------------------------------------------------------- Go to NanTroSEIZE Special Site: http://www.jamstec.go.jp/chikyu/eng/CHIKYU/status.html Go to Expedition 314 Photo Gallery: http://www.jamstec.go.jp/chikyu/eng/Expedition/NantroSEIZE/exp314_pg.html Go to NanTroSEIZE science plan: http://www.jamstec.go.jp/chikyu/eng/Expedition/NantroSEIZE/index.html ======================================== CHIKYU MAIL NEWS To subscribe or unsubscribe, http://www.jamstec.go.jp/chikyu/eng/mailnews/ CHIKYU HAKKEN web site introduces you to every aspect of the Deep Sea Drilling Vessel "Chikyu" and science and technology for the IODP Earth exploration. http://www.jamstec.go.jp/chikyu/ The Integrated Ocean Drilling Program (IODP) is an international marine research drilling program dedicated to advancing scientific understanding of the Earth by monitoring and sampling sub seafloor environments. IODP drilling operations aboard the Chikyu are managed by JAMSTEC through CDEX, Japan Implementing Organization. http://www.iodp.org "CHIKYU HAKKEN" means Discover the Earth in Japanese. =========================================