Morphologic Analysis of Submarine Slope Stability Using Gridded Multibeam Bathymetry and High Frequency Seismic Reflection Profiles

(AGU Poster Section)

L. F. Pratson, U. T. Mello, C. Pirmez, C. Keeley, B. Coakley
(all at: Lamont-Doherty Earth Observatory, Palisades, NY 10964)

Abstract

Infinite slope analysis, which assesses the Coulomb failure potential of saturated, infinite, homogeneous slopes, has been used to estimate submarine slope stability for different continental margin settings (e.g., Mississippi Delta [Prior and Suhayda, 1979], southern Cascadia accretionary wedge [Orange and Breen, 1992]. The estimates are based on general values for the sediment depth z and angle Beta of slip surfaces along which slope failures commonly observed. Improved estimates, which reflect ranges in sediment strength due to spatial variations in pore pressure, local slope, and sediment type, can be derived from analysis of individual slope failures between submarine imaged in multibeam bathymetric grids and high frequency seismic reflection profiles. The bathymetry defines the sea floor slopes and elevations immediately above and adjacent to the heads of the slope failures, while the seismic reflection profiles help constrain the slope and subbottom depth of the slip surfaces along which the failures occurred. Together, these data define the relation between z and Beta at the discrete grid-point locations within the head of each slope failure. Estimates of sediment strength and pore pressures at these locations can then be made by inputting the corresponding z and Beta measures, along with nearby core information on slope angle of frictional resistance (from sediment type) and density, into the Coulomb equation using an orthogonal coordinate system oriented parallel and perpendicular to the dip of the sea floor. Neighboring estimates derived from these measures provide integral slope stability estimates and information on their statistical significance. They may also be used to evaluate possible variations in sediment strength and pore pressures both within and between individual slope failures. Examples of the morphologic analysis applied to shallow planar slides along the mid-east U.S. continental margin will be given.