From: Andy Soos, ENN
Published October 15, 2010 11:41 AM

Haiti Quakes

The magnitude 7.0 earthquake that caused more than 200,000 casualties and devastated Haiti's economy in January 2010 resulted not from the Enriquillo fault, as previously believed, but from slip on multiple faults as well as primarily on a previously unknown, subsurface fault - according to a study published online this week in Nature Geoscience. In addition, because the earthquake did not involve a slip near the Earth's surface, the study suggests that it did not release all of the strain that has built up on faults in the area over the past two centuries, meaning that future surface rupturing earthquakes in this region are likely.

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Geophysicist Eric Fielding of NASA's Jet Propulsion Laboratory, Pasadena, Calif., along with lead author Gavin Hayes of the U.S. Geological Survey and other colleagues from USGS, the California Institute of Technology in Pasadena, the University of Texas at Austin, and Nagoya University, Japan, used a combination of seismological observations, geologic field data and satellite geodetic measurements to analyze the earthquake source. Initially the Haiti earthquake was thought to be the consequence of movement along a single fault -- the Enriquillo -- that accommodates the motion between the Caribbean and North American tectonic plates. But scientists in the field found no evidence of surface rupture on that fault.

The Enriquillo-Plantain Garden fault zone is a system of coaxial left lateral-moving strike slip faults which runs along the southern side of the island of Hispaniola. The fault is named for Lake Enriquillo in the Dominican Republic where the fault zone emerges, and extends across the southern portion of Hispaniola through the Caribbean Sea to the region of the Plantain Garden River in Jamaica.

The researchers found the pattern of surface deformation was dominated by movement on a previously unknown, subsurface thrust fault, named the Léogâne fault, which did not rupture the surface.

Léogâne (a Haiti town) was at the epicenter of the January 2010 earthquake, and a United Nations assessment team that investigated three main towns near Port-au-Prince found that Léogâne was "the worst affected area" with 80 to 90% of buildings damaged and no remaining government infrastructure.

Fielding, who processed synthetic aperture radar interferometry data from a Japan Aerospace Exploration Agency (JAXA) satellite used in the study, said, "I was surprised when I saw the satellite data showed the Haiti earthquake must have ruptured a different fault than the major Enriquillo fault, which everybody expected was the source. Without the radar images, we might still be wondering what happened."

Fielding said NASA images acquired after the earthquake over the major fault zones of Hispaniola by the JPL-built Uninhabited Aerial Vehicle Synthetic Aperture Radar airborne instrument will give scientists much more detailed information should another large earthquake occur in the region in the future.

As of 2010, there have been several major earthquakes in Haiti.

The first was in 1751 in Port-au-Prince. According to French historian Moreau de Saint-Méry, "only one masonry building had not collapsed" in Port-au-Prince, Haiti's capital city.

The second was in 1770 in Port-au-Prince. The city was leveled in this magnitude 7.5 quake, which killed over 200 people.

The third was in May 1842. An earthquake destroyed the city of Cap-Haïtien and other towns in the north of Haiti and the Dominican Republic.

The fourth was in 1946: This 8.0-magnitude quake in Samaná also shook Haiti,producing a tsunami that killed 1,600 people.

A temporary Canadian seismic sensor network of three stations has been established in Haiti along the Enriquillo fault. The network is not considered permanent, but will remain for quite some time. The solar powered stations are in secure locations. These are the first seismic stations ever in the country. The new Léogâne fault has no seismic monitoring.

To read the full study, visit: http://dx.doi.org/10.1038/ngeo977 .

For further information: http://www.jpl.nasa.gov/news/news.cfm?release=2010-337&rn=news.xml&rst=2771

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