Seismotectonics of the Caribbean Region and Vicinity
Extensive diversity and complexity of tectonic regimes characterizes the perimeter
of the Caribbean plate, involving no fewer than four major plates (North America,
South America, Nazca, and Cocos). Inclined zones of deep earthquakes
(Wadati-Benioff zones), 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 crustal seismicity 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 plate moves
westwards with respect to the Caribbean plate at a velocity of approximately 20
mm/yr. Motion is accommodated along several major transform faults that extend
eastward from Isla de Roatan to Haiti, including the Swan Island Fault and the
Oriente Fault. These faults represent the southern and northern boundaries of the
Cayman Trench. Further east, from the Dominican Republic to the Island of Barbuda,
relative motion between the North America plate and the Caribbean plate becomes
increasingly complex and is partially accommodated by nearly arc-parallel subduction
of the North America plate beneath the Caribbean plate. This results in the formation
of the deep Puerto Rico Trench and a zone of intermediate focus earthquakes
(70-300 km depth) within the subducted slab. Although the Puerto Rico subduction
zone is thought to be capable of generating a megathrust earthquake, there have
been no such events in the past century. The last probable interplate (thrust fault)
event here occurred on May 2, 1787 and was widely felt throughout the island with
documented destruction across the entire northern coast, including Arecibo and San
Juan. Since 1900, the two largest earthquakes to occur in this region were the
August 4, 1946 M8.0 Samana earthquake in northeastern Hispaniola and the July 29,
1943 M7.6 Mona Passage earthquake, both of which were shallow thrust fault earthquakes.
A significant portion of the motion between the North America plate and the Caribbean
plate in this region is accommodated by a series of left-lateral strike-slip faults that bisect
the island of Hispaniola, notably the Septentrional Fault in the north and the
Enriquillo-Plantain Garden Fault in the south. Activity adjacent to the Enriquillo-Plantain
Garden Fault system is best documented by the devastating January 12, 2010 M7.0 Haiti
strike-slip earthquake, its associated aftershocks and a comparable earthquake in 1770.
Moving east and south, 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. Here, the
North and South America plates subduct towards the west beneath the Caribbean plate
along the Lesser Antilles Trench at rates of approximately 20 mm/yr. As a result of this
subduction, there exists both intermediate focus earthquakes within the subducted plates
and a chain of active volcanoes along the island arc. Although the Lesser Antilles is
considered one of the most seismically active regions in the Caribbean, few of these events
have been greater than M7.0 over the past century. The island of Guadeloupe was the site
of one of the largest megathrust earthquakes to occur in this region on February 8, 1843,
with a suggested magnitude greater than 8.0. The largest recent intermediate-depth
earthquake to occur along the Lesser Antilles arc was the November 29, 2007 M7.4
Martinique earthquake northwest of Fort-De-France.
The southern Caribbean plate boundary with the South America plate strikes east-west
across Trinidad and western Venezuela at a relative rate of approximately 20 mm/yr.
This boundary is characterized by major transform faults, including the Central Range
Fault and the Boconó-San Sebastian-El Pilar Faults, and shallow seismicity. Since 1900,
the largest earthquakes to occur in this region were the October 29, 1900 M7.7 Caracas
earthquake, and the July 29, 1967 M6.5 earthquake near this same region. Further to
the west, a broad zone of compressive deformation trends southwestward across western
Venezuela and central Colombia. The plate boundary is not well defined across northwestern
South America, but deformation transitions from being dominated by Caribbean/South America
convergence in the east to Nazca/South America convergence in the west. The transition zone
between subduction on the eastern and western margins of the Caribbean plate is
characterized by diffuse seismicity involving low- to intermediate-magnitude (M<6.0)
earthquakes of shallow to intermediate depth.
The plate boundary offshore of Colombia is also characterized by convergence, where the Nazca
plate subducts beneath South America towards the east at a rate of approximately 65 mm/yr.
The January 31, 1906 M8.5 earthquake occurred on the shallowly dipping megathrust interface
of this plate boundary segment. Along the western coast of Central America, the Cocos plate
subducts towards the east beneath the Caribbean plate at the Middle America Trench.
Convergence rates vary between 72-81 mm/yr, decreasing towards the north. This subduction
results in relatively high rates of seismicity and a chain of numerous active volcanoes;
intermediate-focus earthquakes occur within the subducted Cocos plate to depths of nearly 300 km.
Since 1900, there have been many moderately sized intermediate-depth earthquakes in this region,
including the September 7, 1915 M7.4 El Salvador and the October 5, 1950 M7.8 Costa Rica events.
