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Geologists to evaluate future Haiti risks

January 19, 2010 By Rex R Dalton This article courtesy of Nature News.

Hunt for survey markers may reveal crucial data.

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US geologists hope to arrive in Haiti next week to pick through the rubble of the earthquake that struck on 12 January, killing tens of thousands of people. The scientists will hunt for survey markers that could help them better understand the geology of what happened — and perhaps determine where future risk lies.

The stainless-steel pins, usually set in concrete bases, are crucial landmarks for measuring earth movements as small as 1 millimetre. To date, the array of 30 devices in Haiti, and 40 in the Dominican Republic — which shares the island of Hispaniola with Haiti — has yielded the best analysis yet of the local earthquake risk. Finding them could allow researchers to better estimate the likelihood of future fault movements.

Major earthquakes are rare in the region. But in 2008, a team led by Eric Calais, a geophysicist at Purdue University in West Lafayette, Indiana, reported at a Caribbean geology conference that the geodetic markers revealed a dangerous strain build-up along Haiti's Enriquillo fault — enough to produce a magnitude-7.2 quake. Last week's quake, on that fault, was a magnitude 7.0.

Hispaniola sits on the rim of the Caribbean tectonic plate (see ). To the northeast, the North American plate pushes under the Caribbean Plate, driving it westwards along two parallel faults: the Enriquillo fault on the southern side of the island and the Septentrional fault along the north shore. These faults periodically lock, build up strain, then release it in earthquakes. Major quakes have not struck the Enriquillo fault area since 1860.

Calais's team passed its warnings on to the Haitian government, but even developed nations would struggle to set up proper earthquake preparedness in the course of just two years. For now, the focus is on helping to assess immediate geological hazards, such as landslides, and gathering data for future studies of seismic risk.

Calais will be going to the island with Paul Mann, a geologist at the University of Texas at Austin who has described the Enriquillo fault (P. Mann et al. Tectonophysics 246, 1–69; 1995). They will be working with Haitian colleagues in the bureau of mines and energy to take Global Positioning System (GPS) measurements from as many of the geodetic markers as they can, to see how much the fault slipped at different points along its length.

"These benchmarks are extremely important, representing years of data," says Calais. Mann will be looking for surface signs of the fault rupture — called mole tracks because they look like the swell along the surface sometimes produced by the burrowing mammals. Researchers can plug that information into a model to calculate where strain has now built up along the fault and where future quakes might strike.

Seismologists from the universities of Nice and Brest in France will be coming with portable seismometers. UNAVCO, a non-profit consortium in Boulder, Colorado, has provided ten additional GPS receivers to deploy, and more may be coming from other sources, says Calais. And the US Geological Survey hopes to send in a rapid-response team, working with the US Agency for International Development.

Meanwhile, other researchers are trying to get insight into the quake from afar. At the University of Miami in Florida, Tim Dixon and Falk Amelung are looking to see whether space-borne radar interferometers, such as that aboard Japan's Advanced Land Observing Satellite, detected deformation of the terrain before the quake. The satellite is expected to pass over Haiti again this week.

Yet all acknowledge that the science will do little immediate good unless countries are able to incorporate the findings into future preparedness plans.

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