In the first decade of the Integrated Ocean Drilling Program (IODP) 2003–2013, drilling expeditions in the Nankai Trough Kumano transect, the Costa Rica Osa Peninsula transect, and the Japan Trench provided great insights into deformation processes in subduction zone forearcs. In pursuit of the IODP's objective of investigating the onset of seismogenic locking and rupture, the overarching aim of all these transects was to drill into plate boundary fault systems, both at shallow, presumed aseismic levels and at greater, presumed seismogenic depths to study faults and their immediate environment. Closely allied objectives included determination of ages of tectonic and stratigraphic events in marginal wedges, elucidation of hydrogeologic and diagenetic processes in these active margins, and monitoring stress conditions and seismic activity. Taken together, important results from this work include the following: (1) Rapid and localized fault slip can sometimes extend all the way to the trench even where hosted in porous, poorly consolidated marine sediments. This may be due to the frictional properties of the shallow fault zone material; (2) Sediment supply can be high in both erosive and accretionary systems, as recorded by sedimentation rates in forearc basins, but the locus and timing of sedimentation in trench versus forearc/slope basin settings can profoundly impact wedge evolution; (3) Observed principal stress orientations are governed by tectonic convergence but relative stress magnitudes exhibit a more complex relationship with tectonics than previously anticipated; and (4) Strong fluid overpressures are not observed in upper and mid-wedge settings although seismic reflection data suggest that elevated pore fluid pressure may play an important role in fault and wedge strength at depth. Finally, long-term borehole observatories installed at the Nankai Trough and Japan Trench are the first steps toward the goal of monitoring these active plate boundary fault systems over time.
|Title of host publication||Earth and Life Processes Discovered from Subseafloor Environments|
|Subtitle of host publication||Earth and Life Processes Discovered from Subseafloor Environments A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP)|
|Number of pages||41|
|Publication status||Published - 2014|
|Name||Development in Marine Geology|