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Perspective view of the edge of the carbonate platform. Viewing direction is from the NE to the SW. White arrows point to the boundary between multibeam bathymetry and single-beam bathymetry. Black arrows point to fissures in the seafloor. Dotted lines are debris toes. The locations of a previously suggested strike-slip fault (SPRSFZ) and the largest free-air gravity anomaly on Earth (-380 mGal) are shown. Stippled textures (e.g., near SPRSFZ) are multibeam acquisition artifacts.
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Newly-acquired multibeam bathymetry of the entire Puerto Rico trench reveals numerous retrograde slope failures at various scales at the edge of the carbonate platform north of Puerto Rico and the Virgin Islands. The slumped material comprises carbonate blocks, which are cohesive and the edge of the carbonate platform is steeper than most continental slopes, resulting in a higher potential runup than along other U.S. coasts. The style of sliding (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. Fissures, discovered in the ocean floor near the edge of the platform, indicate that the process is expected to continue in the future. Large submarine slides were discovered for the first time also on the northern side of the Puerto Rico trench. One of the slope failures, the Arecibo amphitheater, previously thought to represent a single giant slide with a volume of 900-1500 cu. km, appears to comprise several different slides. The expected maximum runup on the northern coast of Puerto Rico from one of these slides is <20 m, much lower than previously estimated. Although at larger depths (~6000 m), they aim toward Puerto Rico and have large horizontal and vertical dimensions. 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.
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U.S. Department of the Interior |
U.S. Geological Survey