May 18, 2005

U.S. Scientists Unveil Earthquake Forecast

PASADENA, Calif. (AP) -- California residents wondering if tomorrow's forecast will be sunny now can find out if there's also a chance of afternoon tremors.

For the first time, they can check a daily earthquake forecast on the Internet just as easily as they check the weather.

The Web site, maintained by the U.S. Geological Survey, is updated hourly and calculates the probability of strong ground shaking at specific locations over a 24-hour period. The program is not meant to predict when the "Big One" will occur nor serve as a warning signal for residents to evacuate.

Most of the maps will show that the chances of a significant shaking are pretty slim most of the time. USGS seismologist Matthew Gerstenberger said the site would probably be most useful after a strong temblor that has caused significant damage. Since aftershocks are likely in those situations, residents can log online and check for the possibility of more jolting in their area.

Details appear in Thursday's issue of the journal Nature.

California residents already can view real-time earthquake maps with the click of a mouse, but those are usually posted and updated within minutes of a temblor occurring. Now they can click on real-time, color-coded maps that provide earthquake probabilities in a specific region. Areas shaded in red represent a high chance of strong shaking within the next 24 hours (less than a 1 in 10 chance) while those in blue represent a very remote chance, say, more than 1 in a million.

"If there's a red spot, then make sure you've done what you need to do in terms of earthquake preparedness," Gerstenberger said.

The earthquake forecast maps are created by considering a variety of factors, including monitoring the San Andreas Fault and other active faults in California with seismic instruments. Scientists also factor in any recent history of small and large temblors as well as aftershocks, on those same faults.

In an accompanying commentary, Duncan Agnew of the Scripps Institution of Oceanography at the University of California, San Diego, noted that the latest forecast maps give earthquake victims a "much more precise answer" about the risk of aftershocks after a strong tremor. Agnew, who was not part of the project, also said he would like to see the same method applied to other earthquake-stricken countries around the world.


On the Net:

Nature journal: http://www.nature.com/nature

USGS earthquake page: http://earthquake.usgs.gov/