From: Andy Soos, ENN
Published January 25, 2010 04:40 PM

Earthquakes and the Future of Haiti

The aftershock sequence of the magnitude 7 earthquake that struck near Port-au-Prince, Haiti, on Jan. 12, 2010, will continue for months, if not years. The frequency of events will diminish with time, but damaging earthquakes will remain a threat. It is essential that the rebuilding effort in Haiti take into account the potential for, indeed the inevitability of, future strong earthquakes. Haiti is cut by two major plate boundary fault zones. Over the past three centuries, earthquakes comparable to or stronger than the recent one have struck Haiti at least four times, including those in 1751 and 1770 that destroyed Port-au-Prince. It is also not just Haiti that has this potential.

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The geologic fault that caused the Port-au-Prince earthquake is part of a seismically active zone between the North American and Caribbean tectonic plates. The earthquake undoubtedly relieved some stress on the fault segment that ruptured during the event, but the extent of rupture along the fault is unclear at this time.  In historic times, Haiti has experienced multiple large earthquakes, apparently on adjacent faults.  Future quakes have to be anticipated.

Similar earthquakes have happened in what the United States might be considered low risk areas.  The Charleston Earthquake of 1886 was the most damaging quake to hit the Southeastern United States.It occurred at 9:50 p.m. on August 31, 1886, and lasted just under a minute. The earthquake caused severe damage in Charleston, South Carolina, damaging 2,000 buildings and causing $6 million worth in damages, while in the whole city the buildings were only valued at approximately $24 million. Between 60 and 110 lives were lost. Some of the damage is still seen today.

The 1811 and 1812 New Madrid Earthquakes are the most intense intraplate earthquake series to have occurred in the contiguous United States in historic times, beginning with an initial pair of very large earthquakes on December 16, 1811. These earthquakes, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, Louisiana Territory, now Missouri.  Though the seismic rating of the quake was never measured, it has been estimated as high as 8.

There are estimates that the earthquakes were felt strongly over roughly 130,000 square kilometers (50,000 square miles), and moderately across nearly 3 million square kilometers (1 million square miles). The historic 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 square kilometers (6,000 square miles).

These American areas continue to be of potential concern.  What happened in Haiti could happen in St. Louis or Charleston.

Seismic hazard assessments provide the basis for the development of appropriate building codes and the identification of regions at greatest risk. A thorough seismic hazard assessment of Haiti, as well as of other countries in the Caribbean, will provide the basis for establishing or improving building codes and strengthening building resilience over the long term.  The development of more resilient structures and infrastructure is a long term goal, particularly in the face of economic limitations. Over the short term, it is critical that the rebuilding effort be undertaken with an awareness of the potential for subsequent damaging events during the next months and years. It is essential that structures such as hospitals, schools, and critical facilities be reconstructed with greater resilience for the preservation of life and functionality.

For further information:  http://www.usgs.gov/newsroom/article.asp?ID=2385&from=rss&utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+UsgsNewsroom+(USGS+Newsroom)&utm_content=Google+Reader or http://www.jpl.nasa.gov/news/features.cfm?feature=2449&rn=news.xml&rst=2449

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