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ABSTRACT: Steady-State Analysis of a Carbonate-Sediment Slope Failure on Horizon Guyot

W. C. Schwab, R. E. Kayen, H. J. Lee

Slope failure and subsequent mass movement have been identified on a slope of 1.6° to 2.0° on the pelagic sediment cap of Horizon Guyot, Mid-Pacific Mountains, in a zone of strong bottom-current activity. A seismic-reflection survey and submersible investigation of this slope failure shows it to be a slump that contains discrete blocks which have a relief of 6 to 15 m. An evaluation of the stability of the sediment cap suggests that failure resulted from a combination of current-induced beveling of the seafloor and infrequent earthquake loading, accompanied by cyclic strength reduction. A steady-state geotechnical analysis of the sediment indicates a predisposition of deeply buried sediment toward disintegrative flow failure. Although slope failure in this zone ould thus include large amounts of internal deformation, the downslope component of the gravitational stress in the near-surface sediment (subbottom depth <14 m) is insufficient to maintain downslope movement after slope failure. The morphology predicted from the steady-state analysis of coherent slump blocks displaced and rafted upon a weakened zone at depth, corresponds well with seismic-reflection profiles and submersible observations.

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