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ABSTRACT: A Giant Submarine Slope Failure on the Insular Slope North of Puerto Rico: A Response of Arecibo Basin Strata to Tectonic Stress

W. C. Schwab, W. W. Danforth, K. M. Scanlon

An amphitheater-shaped scarp, approximately 55 km across in water depths from about 3000 m to 6700 m was imaged on the northern insular slope of Puerto Rico (southern slope of the Puerto Rico Trench) using the GLORIA side-scan sonar system. This scarp represents the removal of more than 1500 m3 of Tertiary Arecibo basin strata. The head of the scarp coincides with the location of a fault zone observed on nearby seismic-reflection profiles. Interpretation of the GLORIA imagery, and a review of available bathymetric, geophysical, and stratigraphic data and tectonic-framework models suggest that the scarp formed as a consequence of slope failure induced by tectonic oversteepening of the insular slope. The oversteepening may be a result of the most recent episode o convergence of the Caribbean and North American plates, which began approximately 4 million years ago. The Arecibo basin strata have been tilted approximately 4° to the north and are apparently gravitationally unstable under the present seismic regime. The volume of material involved in this slope failure is comparable to the material displaced in tsunamogenic submarine landslides along the Peru Trench and Hawaiian Ridge. Therefore, if the slope failure north of Puerto Rico was catastrophic, it was large enough to have generated a tsunami that would have flooded the low ground of northern Puerto Rico.

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