Scientists scour Haiti for clues to past and potential earthquakes
Friday, February 19, 2010
PORT-AU-PRINCE, HAITI -- As engineers inspect cracked and sagging buildings here, a team of U.S. scientists is probing deeper, hoping to learn what caused the earth to shudder and where it might rumble again.
The task carries significant scientific and practical interest on an island that has what Eric Calais calls "two big, active faults." As he told the National Science Foundation, the sponsor of the research expedition, the 7.0 quake reordered the local geology.
"The big question is, instead of small aftershocks, could there be a bigger earthquake coming?" asked Calais, who is leading the seven-member team. "There are many historical examples of an initial earthquake triggering an even larger one along the same or nearby faults."
In remote terrain that can sometimes be reached only by helicopter or on foot, the scientists are taking measurements and searching for a precise point where the earth might have split open. To their disappointment, they have found no crack.
"It's like detective work," Calais said during a break. "Go into the crime scene, and see the clues that have been left behind."
The scientists think the Jan. 12 earthquake that killed about 200,000 people was shallow, perhaps nine miles below the earth's surface. The crack probably developed sideways, Calais said, and was roughly 31 miles long.
"It's a small segment of a big fault," said Calais, who has been studying Haiti's geology for years. "The way to think about it is, the earthquake is not just the epicenter. An earthquake is much more complicated than that."
Without a split at the surface, the team is looking for other signs that the earth moved laterally, such as a misaligned road or ridge. They also look for fresh rises or dips in the landscape.
"Some areas went up, some areas went down," Calais said, noting that the coastal cities of Leogane and Petit-Goave might have dropped as much as three feet in places. But despite the installation of new sensors and the accumulation of data, scientists are not able to predict what the earth will do next.
"There is no scientific basis for forecasting earthquakes. We don't have a way to do it," Calais said. "The only thing we can say for sure is, there was a risk before the earthquake, and there is still a risk."
Before last month, the last strong earthquake in the area occurred in 1770. Yet Calais, eyeing cement-block houses across a ravine in Petionville, said Haitians would be tapping a "false sense of security" to say that "there's no way it will happen in my lifetime."
Even if an individual makes that calculation, Calais said, Haiti as a nation should not.
"It's important that the rebuilding of the city accounts for this, that the fault has been there, that it is there and will be there," Calais said. "It's been doing its thing for millions of years and probably will be doing its thing for several million years more."