23 August 2007
The Japan Agency for Marine-Earth Science and Technology
The Nankai Trough is located beneath the ocean off the southwest coast of Japan. It is one of the most active earthquake zones on the planet, and one of the best-studied subduction zones in the world. It has a 1,300-year record of generating earthquakes that typically cause tsunamis, including the 1944 Tonankai (M = 8.1) and the 1946 Nankaido (M = 8.3) earthquakes.
The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) attempts for the first time to drill, sample, and instrument the earthquake-causing, or seismogenic portion of Earth's crust, where violent, large-scale earthquakes have occurred repeatedly throughout history.
The plan for NanTroSEIZE includes drilling, below the ocean, very deep into the Earth to observe earthquake mechanisms. Sensors will be installed deep in the subseafloor to record earthquakes up close. Samples will be collected to study the frictional properties of the rock. These sensor and sample data are expected to yield insight into the processes responsible for earthquakes of all kinds. The data may help to understand the behavior of water and its influence on subduction zones.
During Stage 1, six sites will be drilled (red circles on the map below). The targets are the incoming sediment of Shikoku Basin and underlying oceanic crust, the frontal thrust system at the toe of the accretionary wedge, the mid-wedge megasplay fault system, and two approximately 1,000 meter deep holes at sites planned for later deep penetrations of the seismogenic zone faults.
The three Stage 1 expeditions will be implemented as a single science program with samples and data freely shared across all three expeditions. However, each Stage 1 expedition has very different drilling targets and science objectives that must be achieved.
LWD (Logging While Drilling) logging at all Stage 1 sites (6 Sites). These operations consist of continuously drilling one or more holes at each site by drilling down at a controlled rate, with the logging tools incorporated into the bottom-hole assembly a few meters behind the bit. The log data are therefore acquired very soon after the hole is cut, providing the best possible data quality. The LWD operational and science data will be crucial for optimizing the subsequent four Stage 1 expeditions and for planning future stages. There will be 16 scientists on board including:
Riserless coring at the outer edge of the Kumano Basin (1 Site). This site provides an opportunity for investigation of (a) the outer forearc basin depositional systems, including possible earth-quake-triggered turbidites; convergent margin deformation; likely gas hydrates and a BSR (Bottom-Simulating Reflector); and (b) physical properties, fluid and gas chemistry, and hydrogeology in the region near the updip edge of the splay fault system. There will be 25 scientists including:
Riserless coring of frontal thrust (1 Site) and megasplay faults (1 Site) will sample two major thrust fault systems at relatively shallow depths where they are accessible to riserless drilling. The first is the main frontal thrust at the seaward edge of the entire accretionary wedge; the second site will target the shallow portion of the megasplay fault system. The objectives are: a comprehensive characterization of the deformation, evaluation of the inferred depth of detachment and structural partitioning at the décollement, physical properties of the fault zone and surrounding wallrocks, diagenesis, and chemical and other evidence for fluid flow. There will be 25 scientists including:
The Japan Agency for Marine-Earth Science and Technology (JAMSTEC), established in 1971, is the leading marine-earth science research institute in Japan. JAMSTEC's main objective is to contribute to the advancement of academic research in addition to the improvement of marine science and technology by proceeding the fundamental research and development on marine. For more information, please visit http://www.jamstec.go.jp/.
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 started since October 2003 led by Japan and USA. IODP now has 21 member countries. For more information, please visit http://www.iodp.org/