Plate interaction in the NE Caribbean subduction zone from continuous GPS observations

Abstract

Kinematic similarities between the Sumatra and Puerto Rico Trenches highlight the potential for a mega‐earthquake along the Puerto Rico Trench and the generation of local and trans‐Atlantic tsunamis. We used the horizontal components of continuous GPS (cGPS) measurements from 10 sites on NE Caribbean islands to evaluate strain accumulation along the North American (NA) – Caribbean (CA) plate boundary. These sites move westward and slightly northward relative to CA interior at rates ≤2.5 mm/y. Provided this motion originates in the subduction interface, the northward motion suggests little or no trench‐perpendicular thrust accumulation and may in fact indicate divergence north of Puerto Rico, where abnormal subsidence, bathymetry, and gravity are observed. The Puerto Rico Trench, thus, appears unable to generate mega‐earthquakes, but damaging smaller earthquakes cannot be discounted. The westward motion, characterized by decreasing rate with distance from the trench, is probably due to eastward motion of CA plate impeded at the plate boundary by the Bahamas platform. Two additional cGPS sites in Mona Passage and SW Puerto Rico move to the SW similar to Hispaniola and unlike the other 10 sites. That motion relative to the rest of Puerto Rico may have given rise to seismicity and normal faults in Mona Rift, Mona Passage, and SW Puerto Rico.

A geodetic plate motion and Global Strain Rate Model

“…[ Niemi et al ., ; Prawirodirdjo and Bock , ; Wdowinski et al ., ; D'Agostino and Selvaggi , ; Hill and Blewitt , ; Walpersdorf et al ., ; Calais et al ., ; Fernandes et al ., ; Kogan and Steblov , ; Teferle et al ., ; Bechtold et al ., ; Argus et al ., ; Kreemer et al ., ; Le Pichon and Kreemer , ; Hammond et al ., ; Asensio et al ., ; Nocquet , ; ten Brink and López‐Venegas , ; Berglund et al ., ; Malservisi et al ., ; de Lis Mancilla et al ., ; Ganas et al ., ]; Those studies all provided valuable data and interpretations, but we analyze the same stations, with typically (much) longer time series than available in those original studies.…”

Slab tears and intermediate‐depth seismicity

“…The North America plate is obliquely subducting beneath the Caribbean plate along the obtuse northern corner of the Lesser Antilles arc, northeast of Puerto Rico and the Virgin Islands. Subduction under an obtuse corner is expected to create geometric complications and as some have suggested, segmentation of the slab [ ten Brink and López‐Venegas , ; ten Brink , ; Dillon et al ., ; McCann and Sykes , ; Meighan and Pulliam , ; Meighan et al ., ]. An actively propagating slab tear is suggested to be the dominant process affecting local tectonics, based on the trench's bathymetry and negative gravity anomaly, stress changes along the trench corner related to seafloor asperities, timing of the trench collapse, seismic anisotropy, continuous Global Positioning System (GPS) vector analyses, and seismic swarm activity [ ten Brink and López‐Venegas , ; ten Brink , ; Meighan and Pulliam , ; Meighan et al ., ].…”

Assessment of tsunami hazard to the U.S. Atlantic margin

“…Seismic reflection data show normal fault block on the subducting plate being rotated into the trench. ten Brink (2005) interpreted these unusual observations as evidence for a tear in the subducting North American Plate, which caused the trench and its vicinity to founder, and probably decreased the coupling along the subduction interface in the area. Additional observations support this interpretation -for example, GPS observations from Puerto Rico and the Virgin Islands show that these islands are moving northward toward the trench relative to the Caribbean Plate interior, which is the opposite direction to most subduction zone regions where elastic strain accumulates along the subduction interface (ten Brink and López-Venegas, 2012).…”

“…This trench portion also has an unusually deep (7900 m) forearc extending 50 km south of the trench, coincident with the lowest free-air gravity anomaly on Earth (−380 mGal) (ten Brink, 2005). The north shore of Puerto Rico consists of a tilted carbonate platform.…”

“…Another earthquake source near the trench could however, generate tsunamis. The northern wall of the Puerto Rico Trench between 62°W and 66°W is characterized by grabens with up to 1500 m high escarpments (ten Brink, 2005). These escarpments are interpreted as normal faults (Fig.…”