The Puerto Rico trench exhibits great water depth, extremely low gravity anomaly, and a tilted carbonate platform between (reconstructed) elevations of +1300 m and -4000 m. we suggest that these features are manifestations of large vertical movements of a segment of the Puerto Rico Trench, its forearc, and the island of Puerto Rico that took place 3.3 m.y. ago over a time period as short as 14-40 kyr. These vertical movements are explained by a sudden increase in the slab's descent angle that caused the trench to subside and the island to rise. The increased dip could have been caused by shearing or even by a complete tear of the descending North American slab, although the exact nature of this deformation is unknown. The rapid (14-40 kyr) and uniform tilt along a 250-km-long section of the trench is compatible with scales of mantle flow and plate bending. The proposed shear zone or tear is inferred from seismic, morphological, and gravity observations to start at the trench at 64.5W and trend southwestward toward eastern Puerto Rico.
The tensile stresses necessary to deform or tear the slab could have been generated by increased curvature of the trench following a counterclockwise rotation of the upper plate and by the subduction of a large seamount. The model proposed here provides a tectonic framework for the NE Caribbean plate boundary, which will help in the assessment of earthquake and tsunami hazards for Puerto Rico, and the British and U.S. Virgin Islands. Beyond the regional interest, it shows that geological phenomena of the scale observed here can arise from local crustal interactions through coupling between lithosphere and asthenosphere and between horizontal and vertical tectonic forces. Finally, the contrast between the collapsed trench and uplifted island in the Puerto Rico section of the subduction zone, and the adjacent more normal subduction zone of the Virgin Islands, provides constraints on dynamic models of subduction zones. A more detailed study of the history of the collapse of the carbonate platform may help constrain the rheological properties of the slab and its surrounding asthenosphere, and may also provide constraints on rates of reef and platform growth during sea level rise.
Below are other science projects associated with this project.
Caribbean Tsunami and Earthquake Hazards Studies
Caribbean Tsunami and Earthquake Hazards Studies- Stress Changes and Earthquake Hazard
Caribbean Tsunami and Earthquake Hazards Studies-Tsunami Potential
Caribbean Tsunami and Earthquake Hazards Studies- Seafloor Map
- Overview
The Puerto Rico trench exhibits great water depth, extremely low gravity anomaly, and a tilted carbonate platform between (reconstructed) elevations of +1300 m and -4000 m. we suggest that these features are manifestations of large vertical movements of a segment of the Puerto Rico Trench, its forearc, and the island of Puerto Rico that took place 3.3 m.y. ago over a time period as short as 14-40 kyr. These vertical movements are explained by a sudden increase in the slab's descent angle that caused the trench to subside and the island to rise. The increased dip could have been caused by shearing or even by a complete tear of the descending North American slab, although the exact nature of this deformation is unknown. The rapid (14-40 kyr) and uniform tilt along a 250-km-long section of the trench is compatible with scales of mantle flow and plate bending. The proposed shear zone or tear is inferred from seismic, morphological, and gravity observations to start at the trench at 64.5W and trend southwestward toward eastern Puerto Rico.
The tensile stresses necessary to deform or tear the slab could have been generated by increased curvature of the trench following a counterclockwise rotation of the upper plate and by the subduction of a large seamount. The model proposed here provides a tectonic framework for the NE Caribbean plate boundary, which will help in the assessment of earthquake and tsunami hazards for Puerto Rico, and the British and U.S. Virgin Islands. Beyond the regional interest, it shows that geological phenomena of the scale observed here can arise from local crustal interactions through coupling between lithosphere and asthenosphere and between horizontal and vertical tectonic forces. Finally, the contrast between the collapsed trench and uplifted island in the Puerto Rico section of the subduction zone, and the adjacent more normal subduction zone of the Virgin Islands, provides constraints on dynamic models of subduction zones. A more detailed study of the history of the collapse of the carbonate platform may help constrain the rheological properties of the slab and its surrounding asthenosphere, and may also provide constraints on rates of reef and platform growth during sea level rise.
Sources/Usage: Public Domain.Side view of the uniformly tilted carbonate platform and the narrow shelf north of Puerto Rico. (B) Graphical representation of the method used to calculate the duration of the tilt event. Click on image for larger view. - Science
Below are other science projects associated with this project.
Caribbean Tsunami and Earthquake Hazards Studies
Puerto Rico and the Virgin Islands are located at an active plate boundary between the North American plate and the northeast corner of the Caribbean plate. Plate movements have caused large magnitude earthquakes and devastating tsunamis. The USGS has an ongoing program to identify and map the faults in this region using various geophysical and geological methods in order to estimate the location...Caribbean Tsunami and Earthquake Hazards Studies- Stress Changes and Earthquake Hazard
Strike-slip faults in the forearc region of a subduction zone often present significant seismic hazard because of their proximity to population centers. We explore the interaction between thrust events on the subduction interface and strike-slip faults within the forearc region using 3-D models of static Coulomb stress change.Caribbean Tsunami and Earthquake Hazards Studies-Tsunami Potential
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...Caribbean Tsunami and Earthquake Hazards Studies- Seafloor Map
To help understand the origin of the unusual bathymetry, gravity, and vertical tectonics of the plate boundary and to provide constraints for hazard assessment, the morphology of the entire 770-km-long trench from the Dominican Republic in the west to Anguilla in the east was mapped with multibeam echosounder during three cruises in 2002 and 2003. Parts of the Puerto Rico Trench were previously...