ABSTRACT: Quantitative Controls on Submarine Slope Failure Morphology in the Pacific Ocean

Homa J. Lee, William C. Schwab, Brian D. Edwards, Robert E. Kayen

A continuum of morphology has been observed in slope failures of submarine sediment. Two end-members can be distinguished: nondisintegrative, relatively small-displacement slides and disintegrative, relatively large-displacement flows. Slides are seen on high-resolution subbottom profiles that show largely intact blocks translating or rotating along discrete failure planes. In contrast, disintegrative flows typically show larger displacements, evacuated scars, and destruction of original structure.

Quantitative analysis of five known areas of submarine slope failure on the U.S. California and Alaska margins shows that flow failures occur where the sediment initially has a relatively open structure and low density or becomes open as a result of swelling during long loading events. Slides typically occur where the sediment structure is relatively dense. The degree of structural openness is related to steady-state characteristics, which are the density and stress toward which a sediment progresses during shear to large strain. If the sediment density is much lower than the steady-state density, the tendency is toward structural collapse and the resultant disintegrative failure. Sediment densities greater than the steady-state density lead to a tendency toward structural dilation du ing shear and the resultant nondisintegrative failure. The same sediment can fail by either mechanism depending upon the residual strength of the sediment relative to the local down-slope stress, as well as density changes that might occur during loading events. For example, dense sediment can swell during long storm-wave loading and ultimately collapse to produce a disintegrative flow. The same dense sediment likely would not swell during short-term earthquake loading and, if failure occurred, would slide as a coherent mass along a discrete plane.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990