The deep-sea drilling vessel Chikyu, operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), will embark on her next mission, IODP Expedition 338: The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stage 3 – from 3 October to 13 January 2014, in the northwestern Pacific Ocean.
The Nankai Trough Seismogenic Zone Experiment is a drilling project designed to investigate the role of a mega-splay fault on influencing plate boundary slip and subsequent tsunami generation, mechanisms of earthquake and tsunami generation along the Nankai Trough, and the mechanisms controlling the aseismic–seismic transition along the fault system by using boreholes to collect geological samples and conduct in situ measurements of geological properties and monitoring of crustal deformation.
The drilling project consists of four stages in all, with drilling operations planned at several sites along a line orthogonal to the Nankai Trough in the Kumano Basin, offshore of the Kii Peninsula (see Figure 2).
Operations for this expedition included drilling across the shallow part of the mega-splay fault and plate boundary fault to clarify the properties of the fault that may have slipped during past earthquakes and to characterize subsurface distribution of strata, deformation structures, and the state of stress.
In Stage 2, the upper shallow portion of the seismogenic zone was penetrated to decipher its geologic structure and to set up long-term observatories within boreholes to continuously monitor crustal deformation. Also, to characterize the properties of incoming sediment that ultimately influences plate motion in the seismogenic zone, geological features of the sediment was examined and strata temperatures were measured.
In the stage 3 “ultra-deep” drilling is being performed that can reach the seismogenic zone. Operations include direct core sampling and analysis from the fault on which great earthquakes have repeatedly occurred to understand the geologic characteristics of the seismogenic zone.
In the stage 4, long-term observatories will be deployed in the ultra-deep borehole to monitor minor changes in the earthquake fault and its surrounding crust. Future goals include connecting the borehole sensors set up in Stage 2 to a monitoring network called Dense Ocean-floor Network for Earthquakes and Tsunamis, so that real-time data from seismogenic zones can be made available.
Upcoming expedition 338
This year riser drilling is being done to extend the bore hole drilled in FY2010 to approximately 3,600 m below the seafloor. In FY2013, the goal is to extend this hole down to the megasplay fault (approx. 5,200 m below the seafloor). This expedition will collect data on direct core samples, while simultaneously drilling and logging holes (Logging While Drilling [LWD])
Thw Expedition 338 Science Party comprises co-chief Scientists, namely Brandon Dugan, Professor, Rice University, USA; Kyuichi Kanagawa, Professor, Chiba University, Japan; Gregory Moore, Professor, University of Hawaii, USA; Michael Strasser, Professor, Swiss Federal Institute of Technology and 27 selected scientists from IODP member countries.
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Press Release, September 28, 2012