"The big question is instead of small aftershocks, could there be a bigger earthquake coming," Team leader Eric Calais said. "There are many historical examples of an initial earthquake triggering an even larger one along the same or nearby faults. We are concerned for the Dominican Republic, as our preliminary models show that the continuation of the fault in this area is loaded."
"The GPS and geological data gathered by this team will provide important insights into the cause of the January 12, 2010, Haitian earthquake," said Tim Killeen, NSF assistant director for geosciences, "and are essential for evaluating the potential for future earthquakes in the Port-au-Prince area."
"The government needs scientifically informed advice to decide what to do now and in the future when they start thinking about rebuilding," Calais said. "We know how to do the calculations that will tell us if the likelihood of other earthquakes along the fault has increased, but we need information that we can only get by going to the field, making direct observations, and taking measurements on the ground."
The research team has been tracking the build-up of energy along the Enriquillo and Septentrional Faults on the island of Hispaniola, which includes Haiti and the Dominican Republic, using Global Positioning System technology. In 2008, the researchers reported the potential for a magnitude 7.2 earthquake in Haiti and a magnitude 7.5 earthquake in the Dominican Republic.
This time around, the team will find and map the area of the fault that ruptured, resurvey the existing GPS markers, and install 10 new continuous GPS sites to monitor the changes that will occur in the years to come as Earth's crust readjusts.
From GPS measurements at the surface, the team can determine what happened along the fault through its full depth 20 kilometers underground. Precise measurements of this underground movement are critical for validating models of stress changes that can indicate the potential for, and possible magnitude of, future earthquakes, Calais said.
"The shifting stresses in the Earth's crust after a major earthquake can act to effectively clamp or unclamp other faults. If a fault is almost ready to go and the change in stress slightly unclamps it, then it may fail and cause an earthquake," he said. "We think this is what's causing the current sequence of aftershocks, which is mostly concentrated at the western end of the epicentral area, including the recent magnitude 6 aftershock."
The team also will collaborate with University of Miami researchers to collect satellite radar data to map crustal changes before and after the earthquake. This information, when combined with the GPS data, will provide the most precise estimate of the earthquake source, a critical starting point for future studies.
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