The magnitude 7 earthquake that killed as many as 100,000 people in Haiti this week may increase the likelihood of a future quake in Jamaica, according to seismologists who study geological risk.

When aftershocks subside in the coming weeks, Haiti's prospects of another earthquake will plummet, while areas west along the same fault line will see increased seismic pressure, said Stuart Sipkin, a seismologist at the U.S. Geological Survey in Golden, Colorado. It could take decades or a century for the pressure to rupture on the western edge of the fault in Jamaica.

A similar quake flattened the Haitian capital of Port-au- Prince 240 years ago, so long ago that most residents were unaware they were at risk, said Roger Musson, who advises engineers on regional dangers for the British Geological Survey. The 1770 upheaval was part of a string of westward-moving temblors that culminated in Jamaica in 1907, he said.

"In Haiti, there's not been earthquakes in living memory; now it's likely that the stress will be increased on the next segment along," Musson, the agency's head of seismic hazard, said in a telephone interview. However, he added, "You are constantly surprised by earthquakes doing things that they're not supposed to do."

Haiti lies near the eastern end of a fault line between the North American and Caribbean tectonic plates -- massive subterranean sections of the earth's crust that move at about the speed that human fingernails grow, Sipkin said.

Stuck Together

When the two passing tectonic plates get stuck together, pressure builds until it is relieved through a violent movement of earth, Sipkin said.

It probably took about 20 to 30 seconds for the fault to break, said Kate Hutton, a seismologist at the Seismological Laboratory at the California Institute of Technology in Pasadena.

"People probably felt it for longer," Hutton said today in a telephone interview. "People's perception of time slows down when they get really stressed."

A magnitude 7 earthquake releases 30 times more energy than a magnitude 6 quake and 900 times more than one rated a 5, Hutton said. By comparison, the Indian Ocean tsunami that killed more than 230,000 people in 2004 was caused by a magnitude 9.1 temblor, the third-most powerful quake since 1900, according to the U.S. Geological Survey's Web site.

Haiti's Red Cross said as many as 50,000 died in the magnitude 7.0 earthquake that struck Port-au-Prince on Jan. 12, and a third of the city's buildings are destroyed, according the United Nations. The final toll may top 100,000 given the extent of destruction, said Irwin Redlener, director of the National Center for Disaster Preparedness at Columbia University Mailman School of Public Health.

Worst Scenario

The Haiti earthquake was a "worst-case scenario," a shallow rupture in the earth that ripped through a densely populated and poorly constructed city, said Pedro de Alba, professor of civil engineering at the University of New Hampshire in Durham. If the break occurred deeper in the earth, much of the energy would have been absorbed by rock, he said.

"A shallow earthquake is the worst possible kind," de Alba said in a telephone interview today. "Pressure was building up for quite a long time."

De Alba said the probability of a future quake west along the fault line has increased, "but to what extent we simply can't predict."

Haiti is the poorest country in the Western Hemisphere, with 78 percent of the country living on less than $2 a day, according to the Washington-based World Bank. Most of Haiti's buildings were built with un-reinforced cement, according to the British Geological Survey's Musson.

No Rebar

In wealthier countries, masonry is held together with steel rods known as rebar, or reinforcing bar, Musson said. The pliable steel absorbs some of the movement of the earth and prevents brittle cement from crumbling and toppling.

Port-au-Prince is on a 70-kilometer (43-mile) rupture zone extending from the epicenter to the west, Musson said. While it's unlikely another earthquake will occur in the zone once aftershocks subside, anything outside the area is an open question, he said.

Kingston, Jamaica was site of the 1907 quake that killed as many as 1,000 people and damaged every building in the city, according to the U.S. Geological Survey Web site. Kingston is about 300 miles from Port-au-Prince, according to WolframAlpha, an online calculator that determines distance between cities based on geological data.