HR: 1340h
AN: OS23D-1352    [Abstracts]
TI: Submarine slope failures north of Puerto Rico, their estimated recurrence time, and their tsunami potential
AU: * ten Brink, U S
EM: utenbrink@usgs.gov
AF: U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Geist, E L
EM: egeist@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Lynett, P J
EM: plynett@civil.tamu.edu
AF: Dept. of Civil Engineering, Texas A&M University, College Station, TX 77843 United States
AB: New multibeam bathymetry and coincident acoustic backscatter images of the 770-km long Puerto Rico trench reveal numerous slope failures at various sizes north of Puerto Rico and the Virgin Islands. At the edge of the carbonate platform a few tens of km north of Puerto Rico, the failed material comprises carbonate blocks, which slid, at least initially, as coherent rock masses. The style of failure (rock falls and slide blocks vs. debris avalanche and debris flow) appears to be correlated with the thickness of the carbonate layers at the headwall of the slide. Extensional fissures, discovered in the ocean floor near the edge of the platform, suggest that the slope failure process is expected to continue in the future. The displacement of large coherent blocks and the steep slope (up to $45\deg$) at the failure point at the edge of the carbonate platform would imply higher slide velocity, and therefore a higher potential for tsunami runup than along many other U.S. coasts that are covered with clastic sediments. One of the identified failure scars at the edge of the platform, the Arecibo amphitheater, previously thought to represent a single giant slide with a volume of 900-1500 cu. km, appears instead to comprise multiple failures. Simulations of one of the slope failures within the Arecibo Amphitheater predict a maximum runup less than 20 m on the northern coast of Puerto Rico. A minimum recurrence time for slope failures along the edge of the carbonate platform can be estimated assuming that the failure process has continued since the tilting of the platform about 3.5 m.y. ago, that the failures have a characteristic area and thickness similar to those observed and assuming that the edge of the platform was initially straight. Elsewhere along the northwestern margin of the island, a 22-km wide slide scarp was discovered in the Upper Mona rift and could be associated with the 1918 tsunami and earthquake that hit northwestern Puerto Rico. Other large submarine slides were discovered for the first time on the northern side of the Puerto Rico trench on the downgoing North American plate. Because these slides occur in deep water (6000 m), have large horizontal and vertical (20 x 1.5 km) dimensions, and the tsunamis emanating from these slides are directed toward Puerto Rico, they are of particular concern and necessitate further study.
DE: 8105 Continental margins and sedimentary basins
DE: 4564 Tsunamis and storm surges
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting