HR: 1330h
AN: T52C-0276    [PDF]
TI: Development of Overpressures at Nankai Accretionary Prism, Ocean Drilling Program Sites 1173 and 1174
AU: * Gamage, K
EM: kusali@ufl.edu
AF: Dept. of Geological Sciences, University of Florida, BOX 112120, Gainesville, FL 32611 United States
AU: Screaton, E
EM: screaton@geology.ufl.edu
AF: Dept. of Geological Sciences, University of Florida, BOX 112120, Gainesville, FL 32611 United States
AB: In this study, we used a one-dimensional model of sedimentation, initial prism loading, and fluid flow to examine the development of overpressures at the toe of the Nankai accretionary complex. A permeability-porosity relationship was established for hemipelagic sediments from laboratory measured permeabilities as an input to the model. Vertical permeabilities were measured for 10 core samples from the Ocean Drilling Program (ODP) Leg 190, Sites 1173 and 1174, from the upper and lower Shikoku Basin facies. Both sites were drilled along the Muroto Transect through the d\`{e}collement zone or its equivalent. Site 1173 is located 11 km seaward of the deformation front and it represents the undeformed incoming sediments, where as Site 1174 represents sediments within the proto-thrust zone. Although turbidite-rich sediments dominate the Nankai accretionary prism, the d\`{e}collement and underthrust sediments are primarily composed of hemipelagic muds. Using the permeability-porosity relationship, our modeling results indicate excess pore pressures that are greater than 30% of lithostatic pressure at the toe of the prism at a convergence rate of 4cm/yr. These values are slightly lower than previously inferred excess pore pressures estimated from porosity data. Additional runs were conducted to simulate a 10-m thick low permeability barrier at the d\`{e}collement where vertical fluid flow is restricted. The low permeability barrier required a permeability less than 1 x 10$^{-}$$^{19}$ m$^{2}$ to generate excess pore pressures greater than 50% of lithostatic pressure. Modeling was further extended to test the significance of variable prism loading rates due to uncertainties in the convergence rate and affects of lateral stress above the d\`{e}collement.
DE: 4255 Numerical modeling
DE: 5114 Permeability and porosity
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2003 Fall Meeting