Map of the North American - Caribbean tectonic plate boundary. Colors denote depth below sea level and elevation on land. Bold numbers are the years of moderately large (larger than about M7) historical earthquakes written next to their approximate location. Asterisk - Location of the January 12, 2010 earthquake. Barbed lines- boundary where one plate or block plunges under the other one. Heavy lines with half arrows - faults along which two blocks pass each other laterally. Click image for full page view.
|Development of the North American - Caribbean Plate Tectonic Boundary Through Time
|| Click on image to view an animation of Caribbean plate tectonic history from 130 Ma to the present (after Pindell and Barrett, 1990).
Puerto Rico and the Virgin Islands are located at an active plate boundary between
the North American plate and the northeast corner of the Caribbean plate. Plate
movements there have caused large magnitude earthquakes and devastating tsunamis,
but scientists have so far failed to explain the deformation of this complex region
in a coherent and predictable picture, and this has hampered their ability to
assess the seismic and tsunami hazards. It is as if we would try to assess earthquake
hazards in California without knowing of the existence of the San Andreas Fault
system and its rate of motion. The risk to life and economic infrastructure is high,
because 4 million U.S. citizens live along the coastlines of Puerto Rico and the
Virgin Islands. The objective of this project is to provide the understanding needed
to approach the problem of assessment, education and mitigation of tectonic hazards
in Puerto Rico and the Virgin Islands. By determining the likely hazards and their
causative mechanisms and providing this information to government agencies and the
public we may aid in such activities as improvement of building codes, encouraging
safer zoning, and assisting public education for response to hazards.
In the 20th century alone there have been several very large earthquakes north of
Puerto Rico (Ms 7.3 in 1918; Ms 7.8 in 1943; Ms 8.0 in 1946 and four major aftershocks
of Ms 7.6, 7.0, 7.3, 7.1 between 1946 and 1953). Large tsunamis have also hit Puerto Rico
and Hispaniola, reportedly killing 1800 people in 1946 and 40 people in 1918. Images of
the slope north of Puerto Rico disclose massive slope failure scars, as much as 50 km
across, that probably generated tsunamis along the north shore of the island. Other
margins of the island (west, south, and south west) are also associated with massive tectonic
features and may pose addtional hazard.