 |
| USGS earthquake location. |
December 31, 2015 - NICARAGUA - A magnitude 5.7
earthquake hit near the coast of Nicaragua on Thursday at a depth of
36.5 km (23 miles), the U.S. Geological Survey said, but the government
said there were no initial reports of damages.
The
quake struck 92 km (57 miles) west southwest of Rivas at 1057 GMT, the
survey added.
It revised the quake's magnitude down from an earlier
estimate of 5.9.
 |
| USGS shakemap intensity. |
The
government spokeswoman, and wife of President Daniel Ortega, Rosario
Murillo, told the state-run television station that there were no
immediate reports of damages. -
Reuters.
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.
 |
| USGS plate tectonics for the region. |
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 (Magnitude
less than 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.
The boundary between
the Cocos and Nazca plates is characterized by a series of north-south
trending transform faults and east-west trending spreading centers. The
largest and most seismically active of these transform boundaries is the
Panama Fracture Zone. The Panama Fracture Zone terminates in the south
at the Galapagos rift zone and in the north at the Middle America
trench, where it forms part of the Cocos-Nazca-Caribbean triple
junction. Earthquakes along the Panama Fracture Zone are generally
shallow, low- to intermediate in magnitude (Magnitude less than 7.2) and
are characteristically right-lateral strike-slip faulting earthquakes.
Since 1900, the largest earthquake to occur along the Panama Fracture
Zone was the July 26, 1962 M7.2 earthquake.
References for the Panama Fracture Zone:
Molnar,
P., and Sykes, L. R., 1969, Tectonics of the Caribbean and Middle
America Regions from Focal Mechanisms and Seismicity: Geological Society
of America Bulletin, v. 80, p. 1639-1684.
More information on regional seismicity and tectonics
-
USGS.
