Vertical motions of the Puerto Rico Trench and Puerto Rico and their cause

Abstract

[1] The Puerto Rico trench exhibits great water depth, an extremely low gravity anomaly, and a tilted carbonate platform between (reconstructed) elevations of +1300 m and À4000 m. I argue 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. I explain these vertical movements 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 64.5°W and trend southwestwardly 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.

Abrupt Change in Forest Height along a Tropical Elevation Gradient Detected Using Airborne Lidar

“…Most of its landmass emerged from the ocean approximately 4.2 My ago, converting an archipelago of low elevation islands and surrounding marine platforms into high mountaintops [7,11]. The remnants of one such platform surround the Luquillo Mountains at an elevation of about 600 m [6].…”

Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands

“…b Oblique view westward Nat Hazards (2012) 63:51-84 53 subduction zone that conveys parts of the North America and South America Plates beneath the Caribbean Plate. Can this subduction zone, which slants beneath the Lesser Antilles and Puerto Rico, generate thrust earthquakes even though it has failed to do so in recent decades (Stein 1982)? If it does generate such earthquakes, can they attain moment magnitude 8 (McCann 1984;LaForge and McCann 2005) or 9 (Geist and Parsons 2009;McCaffrey 2008)?…”

Bathymetric Terrain Model of the Puerto Rico Trench and the Northeastern Caribbean Region for Marine Geological Investigations

“…However, the North American plate also slides under (or subducts) the Caribbean plate. Similar plate geometry was responsible for the 2004 Sumatra earthquake and tsunami (ten Brink, 2005). The Muertos Trough, with water depths reaching 5,500 meters, is located south of the Dominican Republic, Puerto Rico, and the Virgin Islands.…”

“…Beyond the use of the bathymetric compilation in hazard characterization, the BTM provides a spatially consistent dataset for investigating subduction processes that have created the deepest location in the Atlantic Ocean (ten Brink, 2005), large strike-slip south of the subduction zone (ten Brink and Lin, 2004), large normal faults north of the subduction zones (ten Brink and others, 2004), and an active fold-thrust belt south of Puerto Rico (ten Brink and others, 2009).…”