HR: 1340h
AN: OS23B-1308    [Abstracts]
TI: Overpressure, Low Effective Stress, and Slope Failure in the Ursa Region, Deep-Water Gulf of Mexico
AU: * Sawyer, D E
EM: dsawyer@geosc.psu.edu
AF: The Pennsylvania State University, 542 Deike Building, University Park, PA 16802 United States
AU: Flemings, P B
EM: flemings@geosc.psu.edu
AF: The Pennsylvania State University, 542 Deike Building, University Park, PA 16802 United States
AB: Slope failures are associated with overpressured pore fluids and low effective stresses in the Quaternary strata of the Ursa Region, deep-water Gulf of Mexico. At Ursa, a permeable turbidite sandstone (the Blue Unit) is overlain by a low-permeability mudstone. Overpressure in the mudstone, measured with a pore pressure penetrometer (piezoprobe), begin within a few meters of the seafloor and extend 250-450 meters down to the Blue Unit. The overpressure ratio ($\lambda$$\ast$$=$(Pp$-$Phydrostatic)$\backslash$(Sv$-$Phydrostatic), where Sv is the overburden stress, Pp is pore pressure, and Phydrostatic is the hydrostatic pressure) ranges from 0.8 where the overburden is thin to 0.4 where the overburden is thick. Detachment surfaces, mapped with high resolution 3D seismic data, are associated with zones where effective stresses are low. Four subsurface slumps were mapped and are oriented generally northwest-southeast. Slump surface areas are less than 250 km$^{2}$ and maximum scarp-wall height on the largest slide is $\sim$120 meters. We interpret that asymmetric loading of the Blue Unit by low-permeable mudstone has driven fluids to where overburden is thin, decreased effective stress, and generated slope instability.
DE: 8045 Role of fluids
DE: 5114 Permeability and porosity
DE: 3022 Marine sediments--processes and transport
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting