Haiti's Geology Suggests More Quakes Coming

(Jan. 13) -- The biggest danger now for Haitians overwhelmed by an earthquake that leveled much of Port-au-Prince is the prospect of aftershocks bringing down buildings that were left standing. The threat accentuates both the seismically tenuous nature of the Caribbean and the utter lack of quake preparedness by impoverished Haiti.

Though Hispaniola, the island shared by Haiti and the Dominican Republic, suffered little seismic activity in recent decades, it lies between the North American tectonic plate and the Caribbean plate, which are sliding each year at a rate of about 20 millimeters, a bit less than an inch.

Quakes there may come less frequently than in more temblor-ridden areas like California, where movement along the San Andreas Fault exceeds two inches a year. But despite their infrequency, when earthquakes strike the region they can cause devastation on a massive scale, as the world saw Tuesday with the 7.0-magnitude temblor in Haiti. On Wednesday, the scale of Haitian fatalities was defying all official estimates but has already threatened to exceed many times over the total of worldwide earthquake deaths for all of 2009: 1,783.

Moreover, warned Harley Benz, the scientist in charge of the U.S. Geological Survey's National Earthquake Information Center, some of the dozens of aftershocks of up to 5.9 in magnitude have been large enough to wreak new damage across a building stock largely composed of cinder block construction and unreinforced concrete.

"They can just keep weakening an already weakened infrastructure," Benz said. "It doesn't take a very big aftershock to cause more damage to an already vulnerable building stock."

The Septentrional fault system runs across northern Hispaniola, and the Enriquillo-Plaintain Garden fault system cuts across the south past Port-au-Prince, the capital, and the epicenter of Tuesday's earthquake. Both faults have laid ruin to the cities and towns of Haiti over the centuries, sometimes by triggering deadly tsunamis, and on Tuesday by vibrating Port-au-Prince and surrounding areas for tens of seconds.

And though Tuesday's temblor relieved some of the stress built up in the crust of the earth along the faults, "that doesn't mean there isn't tension on other parts of the fault," Benz noted. "We don't know how much strain has built up."

The U.S. Geological Survey upgraded its monitoring system in the Caribbean for earthquakes and tsunamis following the 2004 quake and tsunami off Sumatra that killed tens of thousands across the Indian Ocean and parts of Southeast Asia. The agency has also produced earthquake-hazard studies for the Caribbean and proposed mitigation suggestions for the region.

But Haiti's earthquake preparedness has been "minimal to none," said William McCann, a seismologist who works for governments across the Caribbean, including the Dominican Republic, and acts as a consultant for the USGS.

"There were just so many problems there and only so much money, and you have to prioritize," McCann said, adding that the neighboring Dominicans could be setting themselves up for the same problems by constructing 30-story buildings in seismically dangerous zones. The Dominican Republic this year is set to start updating 30-year-old building codes whose enforcement has been very poor, McCann said, and Haiti's preparedness has been "in a much more precarious state."

It is a historically painful irony of catastrophes, from hurricanes to terrorism to earthquakes, that governments are most ready to expend resources on preparedness and prevention just after they have been hit by a cataclysm.

When Haiti can move past the rescue stage and into the recovery phase, the focus of a government that was fragile even before the quake and its international supporters must be on rebuilding with the fault lines in mind, McCann said.

"We have the technology to identify the riskiest areas. The hazard you can't control, but the probability of a loss you can control by siting your facilities away from the areas where the shaking would be the strongest," he said. Schools -- where many of Haiti's victims still lay buried -- would be the best place to start, he noted.

Once the world has helped Haiti dig itself out, that may be one of the most important requirements demanded by the U.S. and other donors. Because Haiti is sure to shake again.