I was sent the following information from US researchers that investigated the 2003 earthquakes.
Full PDF of their report is here:
http://tasdevil.com/earthquake_info.pdf
Adrian
Title: Fault researchers show high risk of a future, destructive earthquake in the Cibao Valley and north coast area
A group of researchers led by Dr. Eric Calais of Purude Univ of USA are using GPS geodetic data showing how the Caribbean is presently moving to calculate how stresses are accumulating along the major active faults crossing the island of Hispaniola (Fig. 1). This work was reported at a special session on earthquake hazards at the 18th Caribbean Geological Conf held at the Jaragua Hotel in SD (March 24-29).
- Two main faults cross the island: the Septentrional fault in the Cibao valley and the Enriquillo fault in the Eriquillo valley. Both are long and linear strike-slip faults that resemble the San Andreas fault ofCalifornia. Two other faults are found offshore: the North Hispaniola fault zone and the Muertos fault. These offshore faults are accommodate thrusting motion of the island over the Atlantic andCaribbean (cf. EOS article below for figures to use here).
- The best studied of these faults is the Septentrional fz that was studied in detail by a team led by Dr. Carol Prentice of the US Geological Survey in the late 1990s (cf. attached pdf of the final report/publication for that project). This work which excavated parts of the fault using a backhoe showed that the SFZ was an active fault that can be traced the length of the Cibao valley. Dating of young sediments uncovered in the fault excavations showed that the SFZ near Tenares and El Licey has not moved - or has remained “locked”- since a M7 earthquake that broke the fault in the prehistoric interval between AD 1040 and AD 1230. For that reason the central part of the SFZ has accumulated over 4.8 m of potential slip that can be released at any time to produce an earthquake predicted to be greater than M7.
- The SFZ passes within 10 km of the rapidly developing city of Santiago, the Santiago airport, Moca, Monte Criste, Salcedo and Samana. Sudden motion on a fault of this size in such close proximity to urbanized areas may result in widespread loss of life, building and bridge collapse, landslides, fires, ruptured water, sewage and gas pipelines, ruptured dams and bridges, and broken electrical transmission wires. Shock waves would be smaller since they dissipate with distance - but waves originating in the Cibao Valley could still affect Santo Domingo.
- Well known destructive earthquakes occurring on other parts of the Caribbean plate boundary include the 1692 earthquake of Port Royal, Jamaica (magnitude unknown; between 1000-3000 fatalities), the 1972 Managua earthquake (M6.2; 6000 dead) and the 1976 Guatemala earthquake (M6.8; 25,000 dead). Smaller M6 earthquakes occurring within densely populated and urbanized areas like theCibao Valley can be more deadly than much larger M7 events that occur on more distant faults. The earthquake fault of the Managua earthquake ran directly beneath the downtown area and destroyed 90% of the city, much of which remains unbuilt.
- The 1842 Hispaniola earthquake was so destructive and lethal (exact death toll unknown) that it helped Dominicans win independence from Haiti in 1844. Researchers think that the 1842 earthquake may have been a rupture of the SFZ in the western Cibao Valley and area north of Haiti. The 1972 Managua earthquake helped destabilize the Somoza dictatorship and contributed to a protracted civil war from 1979 to 1990.
- Calais et al. have also included the effects of historical earthquakes that have affected the island in 1842, 1948, and 2002. The effect of some large earthquakes is to relieve stress on faults while other earthquakes act to increase stress on faults and make them more susceptible to the sudden fault failure that would produce a large earthquake.
- The new Calais fault stress model shows that historical earthquakes in the northern part of the island have increased stresses on the SFZ and the North Hispaniola fault in the area of the Cibao Valley, the Cordillera Septentional, and tourist areas including the city of Puerto Plata, Sosua and the Puerto Plata airport (cf. his attached map of red zones).
- Stresses are lower along the Enriquillo fault in the southern, less populated part of the island in part because large earthquakes moved through that area in the 18th century and acted to reduce the stress build up.
- As concluded in the earlier Prentice et al. study, the Cibao Valley remains a zone of high risk for an earthquake calculated to be greater than M7. The infrequent occurrence of large earthquakes should not be interpreted by the public and government authorities to mean that there is less earthquake hazard through time. On the contrary, infrequent earthquakes means that large faults are locked, building up stress in the form of elastic energy in the earth’s crust that is eventually released in a destructive event. An analogy is that the crust in the northern part of the island is like a large rubber band that has been pulled back for over 800 years and is now near the threshold of breaking to produce a large earthquake.
The Calais study warns civilian, civil defense, and military authorities to make preparations for a large earthquake of this size in the Cibao Valley. The most recent earthquake of 22 Sept 2003 was M6.5 and resulted in 4 fatalities and minor building damage. The complete “pancake-style” collapse of a three story, concrete slab elementary school near Puerto Plata did not produce fatalities since the main shock of the earthquake occurred when the building was unoccupied by the xxx teachers and students at 12:45 pm local time. Earthquakes that occur during working hours can be more lethal since multistory office buildings, airports, major highways and overpasses that are more prone to sudden collapse are full of people and cars.
Related web links for more information on risk of large earthquakes in the DR:
Maps showing recent earthquakes in Hispaniola:
Welcome to the U.S. Geological Survey Earthquake Hazards Program
General description of 2003 eq at:
http://www.ig.utexas.edu/outreach/dr...q_EOS_2004.pdf
Maps of 2003 damage areas compiled by CODIA at:
Dominican Republic Earthquake - 22 September 2003
How homeowners can protect property before a large earthquake:
Esta Usted Preparado Por Un Terremoto?
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Timebomb in Santiago
