Tectonic Summary
Seismotectonics of the Caribbean Region
Extensive diversity of tectonic regimes characterizes the perimeter of the Caribbean plate, involving no fewer than four major adjacent plates (North America, South America, Nazca, and Cocos). Inclined zones of deep earthquakes (Wadati-Benioff zones), deep ocean trenches, and arcs of volcanoes clearly indicate subduction of oceanic lithosphere along the Central American and Atlantic Ocean margins of the Caribbean plate, while shallow seismicity and focal mechanisms of major shocks in Guatemala, northern Venezuela, and the Cayman Ridge and Cayman Trench indicate transform fault and pull-apart basin tectonics.
Along the northern margin of the Caribbean plate, the North America moves west, relative to the Caribbean plate, at approximately 20 mm/yr, resulting in major transcurrent faults and troughs. Farther east, the North America plate subducts beneath the Caribbean plate resulting in surface expression of the deep Puerto Rico Trench and a zone of intermediate focus earthquakes in the subducted slab. The plate boundary curves around Puerto Rico and the northern Lesser Antilles where the plate motion vector of the Caribbean plate relative to the North and South America plates is less oblique, resulting in active island-arc tectonics. The North and South America plates subduct beneath the Caribbean plate along the Lesser Antilles Trench at rates of about 20 mm/yr; consequently, there are both intermediate focus earthquakes within the subducted South America plate and a chain of active volcanoes along the island arc.
The southern Caribbean plate boundary along with the South America plate strikes east-west across Trinidad and western Venezuela and is characterized by major strike-slip faults and shallow seismicity, resulting from relative plate motion of about 20 mm/yr. Further to the west, a broad zone of convergent deformation trends southwest across western Venezuela and central Columbia. Plate boundaries are not well defined across northern South America, but there is a transition from Caribbean/South America convergence in the east to Nazca/South America convergence in the west, described in more detail below. The transition zone is characterized by high seismic hazard. The Nazca-Caribbean plate boundary offshore of Columbia is characterized by convergence (Nazca plate subducting under South America plate) at about 65 mm/yr. The 6 January 1906 Mw = 8.5 megathrust subduction earthquake occurred on a shallow-dipping interface of this plate boundary segment. Along the western coast of Central America, the Cocos plate subducts beneath the Caribbean plate at rates of 72?81 mm/yr, resulting in a relatively high seismic hazard and a chain of numerous active volcanoes; here intermediate-focus earthquakes occur within the subducted Cocos plate to depths of nearly 300 km.
Extensive diversity of tectonic regimes characterizes the perimeter of the Caribbean plate, involving no fewer than four major adjacent plates (North America, South America, Nazca, and Cocos). Inclined zones of deep earthquakes (Wadati-Benioff zones), deep ocean trenches, and arcs of volcanoes clearly indicate subduction of oceanic lithosphere along the Central American and Atlantic Ocean margins of the Caribbean plate, while shallow seismicity and focal mechanisms of major shocks in Guatemala, northern Venezuela, and the Cayman Ridge and Cayman Trench indicate transform fault and pull-apart basin tectonics. The depth profile panels on this map portray earthquakes that extend from the Middle America Trench axis in the west to depths as great as 300 km beneath Guatemala, and from the Lesser Antilles Trench axis in the east to depths of approximately 200 km beneath Guadeloupe and the northeast Caribbean. In contrast, seismicity along the segments of the Caribbean plate margins from Guatemala to Hispaniola and from Trinidad to western Venezuela is indicative of transform fault tectonics.
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