HR: 1330h
AN: OS22A-1148    [PDF]
TI: Landslide Deposits, Cookie Bites, and Crescentic Fracturing Along the Northern Puerto Rico-Virgin Islands Margin: Implications for Potential Tsunamigenesis
AU: * Hearne, M E
EM: meh6838@uncw.edu
AF: UNC Wilmington Center for Marine Science, 5600 Marvin K. Moss Lane, Wilmington, NC 28409 United States
AU: Grindlay, N R
EM: grindlayn@uncw.edu
AF: UNC Wilmington Center for Marine Science, 5600 Marvin K. Moss Lane, Wilmington, NC 28409 United States
AU: Mann, P
EM: paulm@utig.ig.utexas.edu
AF: University of Texas at Austin Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759-8500 United States
AB: The seismogenic North America-Caribbean oblique-slip plate boundary forms the 8-km-deep Puerto Rico trench north of the densely populated islands of Puerto Rico and Virgin Islands (combined population of just over 4 million people). The southern slope of the Puerto Rico trench adjacent to the Puerto Rico-Virgin Islands (PRVI) carbonate platform is characterized by frequent seismicity, rapid trenchward tilting, oversteepened slopes, and mass wasting. We present high-resolution bathymetry, HMR1 sidescan imagery, and single-channel seismic data to document extensive landslide deposits that we infer to have been the result of multiple slide events capable of producing prehistoric tsunamis along the coasts of Puerto Rico and the Virgin Islands. Landslide deposits can be traced upslope to two, 45-55 km-wide arcuate-shaped embayments or "cookie bites" carved out of the PRVI platform. Three-dimensional visualization of the debris field and the slope of the largest of the arcuate-shaped embayments centered at $66\deg$40' constrain volume removal to 1.1 km$^{3}$ of the PRVI carbonate platform and underlying volcanic and volcaniclastic basement. Sidescan sonar and single-channel seismic data reveal crescentic cracks in the seafloor of the PRVI platform 35-45 km in length located 35 km offshore the northwestern tip of Puerto Rico. These cracks, interpreted to represent the sites of future breakaway scarps and landslides, are similar in shape and length to the head wall scarps of the amphitheaters to the east. An $\sim$500 km$^{2}$ section of the PRVI platform (750 m thick) has begun to detach and slump trenchward along the larger of these cracks. Investigation of the existing arcuate-shaped embayments is essential because massive (tens to hundreds of km$^{3}$) and instantaneous slope failure has the potential to be tsunamigenic. Puerto Rico and the Virgin Islands were inundated by tsunamis in 1867 (mainly affecting St. Thomas and St. Croix, 7 m of runup, casualties in the hundreds) and 1918 (mainly affecting western and northwestern Puerto Rico; 6 m of runup, 120 casualties). Calculation of the potential volume, runout extent, and triggering mechanisms of past submarine landslides will better constrain the tsunamigenic potential of the newly discovered crescentic faults.
DE: 1724 Ocean sciences
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting