| http://www.mcclatchydc.com/world/story/83486.html The danger of another earthquake in Haiti is high enough that scientists are suggesting people sleep in tents. By FRED TASKER ftasker(at)MiamiHerald.com The chance of another big earthquake in Haiti in the near future is great enough that people in Port-au-Prince should sleep in tents -- not even in buildings that survived the Jan. 12 quake apparently unscathed, geologists said Monday. A report by the United States Geological Survey says the probability of an aftershock of magnitude 7 or greater in Haiti in the next 30 days is 3 percent, the probability of one magnitude 6 or greater is 25 percent, and of one magnitude 5 or greater is about 90 percent. ``Three percent may not sound big, but it is pretty big in terms of what we might have expected after a standard earthquake,'' said Dr. Tim Dixon, professor of geophysics at the Rosenstiel School of Marine and Atmospheric Science in Miami. In a typical earthquake, the probability of another quake of the same magnitude that soon would be ``vanishingly small, close to 0,'' he said. TENTS ARE SAFEST He went on: ``If people are in tents, they're quite safe. I would advise them not to move into buildings -- even ones that have been declared safe. And they shouldn't put up a tent beside a tall building.'' In the complex terminology of earthquake measurements, a 6.0 earthquake is only 1/32nd as powerful as a 7.0 quake, and a 5.0 quake is 1/32nd as powerful as a 6.0. But the USGS report warns: ``Any aftershock above magnitude 5.0 will be widely felt and has the potential to cause additional damage, particularly to vulnerable, already damaged structures.'' In the three weeks since the Jan. 12 quake of magnitude 7.0, Haiti has had 63 aftershocks, ranging from magnitude 4.0 to 5.9, the USGS says. CONSTANT THREAT The aftershocks are decreasing. On Jan. 13, the day after the big quake, the Haiti region had 31 aftershocks from magnitude 4.2 to 5.9. Since Jan. 22 there have been only seven -- from 4.0 to 4.8. That's to be expected, said Dr. David Applegate, a seismologist with the USGS. But it doesn't lessen the probability of more aftershocks. ``This is the fiendish thing about earthquakes,'' he said. ``A hurricane hits and moves on; after an earthquake, just because the aftershocks are decreasing doesn't mean we can't have another large quake.'' He called Dixon's advice to sleep in tents ``a reasonable idea.'' One big concern is that the area of the fault zone that did not rupture during the big Jan. 12 quake is closer to Port-au-Prince than the part that did rupture, Dixon said. The Enriquillo Fault Line that caused the big quake starts in Jamaica to the west and runs east through Haiti, about 10 miles south of Port-au-Prince, and on east into the Dominican Republic, Dixon said. The part that ruptured started about 20 miles southwest of the city and ran west for about 30 miles, leaving the rest of the 300-mile fault line intact -- both to the east and the west. When this happens, it can increase seismic pressure on the fault line on both sides of the rupture, Dixon said. The area of most concern now lies east of the big quake's epicenter, only about 10 miles south of Port-au-Prince. The Enriquillo fault line is on the boundary of the massive North American and Caribbean tectonic plates, which slide across each other at a rate of about an inch a year. Looking at the longer term, the Jan. 21 USGS report says, ``...satellite and airborne imagery suggests that the segment of the Enriquillo fault east of the Jan. 12 epicenter and directly adjacent to Port-au-Prince did not slip appreciably in this event. This implies that the Enriquillo fault zone near Port-au-Prince still stores sufficient strain to be released as a large, damaging earthquake during the lifetime of structures built during reconstruction.'' MOVING A CITY The USGS report concludes: ``It is essential that the rebuilding effort in Haiti take into account the potential for, indeed the inevitability of, future strong earthquakes.'' Dixon advised rebuilding the city at least 15 miles north of its present location. The USGS report advises at least a thorough seismic hazard assessment as well as better building codes. |