New Seafloor Map of the Puerto Rico Trench Helps Assess Earthquake and Tsunami Hazards

Details New Seafloor Map of the Puerto Rico Trench Helps Assess Earthquake and Tsunami Hazards New Seafloor Map of the Puerto Rico Trench Helps Assess Earthquake and Tsunami Hazards

Sep 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004eostr..85..349t&link_type=abstract

EOS Transactions, AGU, Volume 85, Issue 37, p. 349-354

Physics

Geophysics

4

Tectonophysics: Dynamics, Gravity And Tectonics, Seismology: Seismic Hazard Assessment And Prediction, Marine Geology And Geophysics: Seafloor Morphology And Bottom Photography

Scientific paper

The Puerto Rico Trench, the deepest part of the Atlantic Ocean, is located where the North American (NOAM) plate is subducting under the Caribbean plate (Figure 1). The trench region may pose significant seismic and tsunami hazards to Puerto Rico and the U.S. Virgin Islands, where 4 million U.S. citizens reside. Widespread damage in Puerto Rico and Hispaniola from an earthquake in 1787 was estimated to be the result of a magnitude 8 earthquake north of the islands. A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918. Large landslide escarpments have been mapped on the seafloor north of Puerto Rico, although their ages are unknown. The Puerto Rico Trench is atypical of oceanic trenches. Subduction is highly oblique (10°-20°) to the trench axis with a large component of left-lateral strike-slip motion. Similar convergence geometry is observed at the Challenger Deep in the Mariana Trench, the deepest point on Earth. In addition to its extremely deep seafloor, the Puerto Rico Trench is also characterized by the most negative free-air gravity anomaly on Earth, -380 mGal, located 50 km south of the trench, where water depth is 7950 m (Figure 2). A tilted carbonate platform provides evidence for extreme vertical tectonism in the region. This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. Then, at 3.5 Ma, the carbonate platform was tilted by 4° toward the trench over a time period of less than 40 kyr, such that its northern edge is at a depth of 4000 m and its reconstructed elevation on land in Puerto Rico is at +1300 m (Figures 1 and 2).

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