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Drilling along the Nankai Trough

 

Description

Nankai TroughThe Nankai Trough is one of the world's best studied seismogenic subduction zone, where large megathrust earthquakes have repeatedly occurred every 90-150 years. The last major earthquakes in this region occurred in 1944 and 1946, and the next earthquake is anticipated in the middle of this century.
In order to investigate the seismogenic megathrust, the IODP project NanTroSEIZE was proposed and is going on its authorizing process to drill south off Kii Peninsula, in the central part of the Nankai Trough. The drill holes of NanTroSEIZE are planned to reach the seismogenic fault, and the actual fault material will be sampled and investigated. The NanTroSEIZE project also emphasizes the importance of monitoring, and includes a scope of monitoring of the fault zone using the IODP hole.
Here we propose that additional boreholes on the continental side by ICDP drilling will make the monitoring of the plate boundary megathrust much more effective and attractive because we have more flexibility for instrumentation and operation of the boreholes. There is a high sensitivity seismic network as well as a dense continuous GPS monitoring network being operated in Japan. By integrating monitoring at the surface and at the depth, the best monitoring system for the plate boundary megathrust in the world will be completed, and the earthquake sciences will be highly benefited.
Candidate items to be monitored at the boreholes include fluid pressure, volumetric strain, 3-component strain, temperature, tilt, seismic waveform, and so on. As a tentative plan, we propose an array of 5 boreholes, 3 or 4 along the Kii Peninsula coast, and 1 or 2 further inland along the IODP transect. The average spacing between boreholes will be about 50 km.

This drilling is aimed at comprehensive understanding of physical/chemical processes related to the recurrence of megathrust earthquakes in and around the plate interface. During an earthquake cycle, variations in the interplate coupling strength cause cyclic stress/strain accumulation and release in the surrounding region. Well coordinated monitoring between the borehole array and the seismic as well as geodetic network at the surface will provide the best coverage over the target. On the other hand, physical properties of the fault zone such as permeability and frictional property are also considered to show cyclic behaviors in accordance with the earthquake cycle, which can be investigated mainly by studying IODP core samples.
From recent precise monitoring with seismological as well as geodetic techniques, new features of the plate boundary processes have been found. They are episodic slow slip events and non-volcanic low frequency tremors. Both phenomena seem to be occurring around the deeper extension of the seismogenic zone along the subducting plate interface. Seismological features of low frequency tremors indicate crustal fluid is playing an important role. Therefore, one of the important scientific target of this drilling is to monitor a hydrological aspect of the crust. For that purpose, we have an idea to monitor pore pressure changes with an array of deep boreholes both in the ocean bottom and on land.
Finally, establishment of basic technologies required for long-term borehole monitoring over an entire earthquake cycle is also highly anticipated.

 (Figure ©:T. Sagiya)


 

Location

Asia, Japan, Honshu, Kii Peninsula

 

Coordinates

34° N, 136° E (Please scroll down to end of page for more information.)

 

Project Start and End
  • not yet determined

 

Programs and Funding

 

Principal Investigators
  • Takeshi Sagiya, Nagoya University, Graduate School of Environmental Studies, Department of Earth and Enviromental Sciences, Earth and Planetary Sciences
  • Kelin Wang, Geological Survey of Canada, Natural Resources Canada, Pacific Geoscience Center, Cordilleran and Continental Margin Tectonics
  • Naoji Koizumi, National Institute of AIST, Geological Survey of Japan, Institute of Geology and Geoinformation, Tectono-Hydrology Research Group

 

Cooperating Principal Investigators

No Co-PIs found for this project

 

Partners and Contractors

 

Keywords

Active Faulting, Collision Zones, Convergent Margins, ICDP-2006/07, IODP, Japan, Kii Peninsula, Monitoring, NANKAI, Nankai Trough, Pore Pressure, Subduction Zone

 

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