# 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.