Investigation of submarine landslide deposits the northern margin of Puerto Rico

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Meghan E. Hearne (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Nancy Grindlay

Abstract: The seismogenic northeastern North America-Caribbean oblique-slip plate boundary includes the 8.5-km deep Puerto Rico trench, 120 km north of the densely populated islands of Puerto Rico and the Virgin Islands. The northern insular margin of Puerto Rico, adjacent to the Puerto Rico trench, is characterized by frequent seismicity, rapid Neogene trenchward tilting, and oversteepened slopes. Multibeam bathymetry, sidescan sonar, and single-channel seismic reflection data reveal extensive submarine landslide deposits on the margin that can be traced upslope to two large (up to 55-km wide and 6.1-km deep) amphitheater-shaped headscarps along the edge of the Puerto Rico –Virgin Islands (PRVI) carbonate platform. The crown of the larger, westernmost scarp incises the platform at 2600 meters below sea level, ~ 40 km off the north coast of Puerto Rico. The associated submarine landslide deposits extend up to 80 km trenchward, covering a total seafloor area of 4313 km2. Seismic reflection data show a maximum debris deposit thickness of 2850 m. The debris deposit consists of multiple layers each approximately 200 m thick. This suggests that the slope failure may have occurred as multiple failure events, rather than a single catastrophic event. Allowing for compaction of the debris deposit sediments, the volume of 1378 km3 for the amphitheater is comparable to the calculated compacted landslide debris volume of 1426 km3. These results suggest that the collection of submarine landslide units is associated with the formation of the giant amphitheater over time. This also suggests that the debris is not being removed by translation or subduction, unlike other convergent margins. Although the exact triggering mechanism(s) for the submarine landslides is not known, tectonic erosion related to the westward migration of the overthickened (20+ km) southeastern Bahamas Province beneath the PRVI margin is a likely candidate. The present-day collision zone is interpreted to be offshore northwestern Puerto Rico, an area characterized by mid-slope uplift, anomalously high seismicity and crescentic cracks in the PRVI carbonate platform that are similar in size and shape to amphitheaters observed further to the east. Evidence of multiple, Pliestocene and younger submarine landslide deposits adjacent to the uplifted Mona Block and within the Mona Rift suggest that the devastating 1918 tsunami could have been generated by a seismically triggered submarine landslide. Moreover, the proximity of crescenticshaped seafloor cracks to the tectonically active Mona Rift make them likely candidates for sites of future breakaway scarps and catastrophic submarine landslides. A modern day inundation would have detrimental effects on Puerto Rico whose population has dramatically increased over the past century to about 3.89 million.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Keywords
Landslides--Puerto Rico, Marine sediments--Puerto Rico, Submarine geology--Puerto Rico, Submarine topography--Puerto Rico Trench region, Submarine trenches--Puerto Rico
Subjects
Landslides -- Puerto Rico
Submarine topography -- Puerto Rico Trench region
Submarine trenches -- Puerto Rico
Marine sediments -- Puerto Rico
Submarine geology -- Puerto Rico