Experts: Utah’s Worst Quake Could be Magnitude 7.4

April 24, 2008

Government geologists have a clearer picture of what The Big One might look like in Utah.

The U.S. Geological Survey has published new hazard maps, which show that the worst-case earthquake has been elevated to magnitude 7.4 on the 240-mile Wasatch Fault that runs from Malad, Idaho, through the state’s population centers to Gunnison.

The report said devastation could span several Wasatch Fault segments at once. Previous maps called for less shaking.

Tall buildings probably would shake less than previously predicted, while buildings of two stories or less might shake harder.

New faults have been discovered, including one south of Tooele, one under Utah Lake and another in northern Utah’s Cache Valley.

The latest maps show much of the United States is on shaky ground, with 46 states facing serious seismic threats. The new maps come just days after a magnitude 5.2 earthquake in southern Illinois.

USGS last published nationwide hazard maps in 2002 and 1996. But research done in the years since has allowed the federal agency to work with experts at universities, professional groups and state agencies, including the Utah Geological Survey, to gather the latest information.

The agency timed the release of the new maps with a national revision of the model building codes used by state and local government to ensure buildings, bridges, highways and utilities can resist earthquake damage.

The National Seismic Hazard Maps are a series of maps and data sets that project the ground shaking that might happen at points throughout the country.

Insurance companies use the data to set rates in some places. Engineers use the maps to forecast landslides and the stability of hillsides.

Federal environmental regulators use the maps to ensure waste-treatment facilities will hold up. Emergency planners use the information to decide how to allocate money for education and preparedness.

In Utah, they serve as a basis for building codes.

Source: The Salt Lake Tribune.

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