Research

My research explores the hydrogeology of the Nankai accretionary prism (located offshore of Japan).  At subduction zones, one tectonic plate subducts under another, and the offscraped sediment is accreted into a prism (Figure 1).  As sediments accrete, they deform like soil in front of a bulldozer.  I seek to understand how fluid pressure and deformation are coupled in this dynamic system.  The interactions of pressures and strain in soils have long been understood from lab experiments—in compressible, low permeability sediments, a rapid strain event results in an abrupt increase in the fluid pressure of surrounding sediments and an ensuing dissipation (Lambe and Whitman, 1979).  These coupled processes of fluid flow and deformation are still poorly understood in active geological settings such as the Nankai.  Research in this field is important to understanding the generation of the Nankai’s frequent, periodic earthquakes. 

The data for my research comes from well installations called ACORK's (Advanced Circulation Obviation Retrofit Kits).  The ACORK's continuously monitor fluid pressures in isolated intervals of surrounding sediments.  Two ACORK's were deployed in boreholes in the Nankai region during ODP Leg 196 (Figure 2).  I use the ACORK data to look for evidence of fluid pressure responses to strain (pressure transients).  I plan to use the pressure transients that I identify to model the mechanical and hydrologic properties of sediments in the accretionary prism and the strain that produced the transients.  I will then develop a conceptual model of fluid flow and strain interdependencies in the prism. 

I hope to answer several fundamental questions about the hydrology and mechanics of the Nankai accretionary prism:

  • Can pressure records be used to map strain in low permeability sediments?

  • How does structure control fluid flow in the accretionary prism?  Specifically, which faults in the accretionary prism act as drains for fluids and which act as barriers? 

Figure 1: Schematic cross section of the Nankai accretionary prism and location of ACORKs.

 Figure 2: Photo of ACORK installation (from Ocean Drilling Program website).