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Federal geological agency increases earthquake risk for about half of U.S.

Thursday, July 17, 2014 | 2:56 p.m. CDT; updated 6:43 p.m. CDT, Thursday, July 17, 2014

WASHINGTON — A new federal earthquake map dials up the shaking hazard just a bit for about half of the United States and lowers it for nearly a quarter of the nation.

The U.S. Geological Survey updated Thursday its national seismic hazard maps for the first time since 2008, taking into account research from the devastating 2011 earthquake and tsunami off the Japanese coast and the surprise 2011 Virginia temblor.

Most of the changes are slight. Project chief Mark Petersen said parts of Washington, Oregon, Utah, Oklahoma, Colorado, Wyoming and Tennessee moved into the top two hazard zones.

Parts of 16 states have the highest risk for earthquakes: Alaska, Hawaii, California, Oregon, Washington, Nevada, Utah, Idaho, Montana, Wyoming, Missouri, Arkansas, Tennessee, Illinois, Kentucky and South Carolina.

Also, Colorado and Oklahoma saw increased risk in some parts and moved up to the second of the seven hazard classifications, he said.

There are major faults and quake hazards along the entire west coast, with an increased concern in the Cascadia region of Oregon. Southern Alaska, the big island of Hawaii, Charleston and the New Madrid fault area of Missouri, Tennessee, Arkansasand Illinois round out the biggest hazard areas.

But shaking hazards are nearly everywhere.

Much of the country west of the Rockies, along with parts of Oklahoma and Tennessee and sections of central Arkansas, northern Alabama, Georgia, South Carolina, Indiana, Illinois, Ohio, Michigan, Virginia, New York and New England saw an increase in shaking hazards for small buildings like houses.

At the same time much of North Carolina, the northern tip of South Carolina, patches of Texas, New Mexico, Oregon, Utah, Nebraska, Arkansas, Kentucky, Tennessee, Ohio, Pennsylvania and New York saw hazard levels lower slightly. And using a different type risk analysis for tall buildings the shaking hazard in New York City dropped ever so slightly, Petersen said.

Petersen said the maps sidestep the issue of earthquakes created by injections of wastewater from oil and gas drilling in Oklahoma and other states, saying those extra quakes weren't included in the analysis. So far this year, nearly 250 small to medium quakes have hit Oklahoma.

Much of the research and cataloging was done by the nuclear industry in response to the quake and tsunami that crippled Japan's Fukushima Daiichi Nuclear Power Station. And researchers at the University of California, Berkeley came up with a better model to simulate shaking, Petersen said.

"I see it as a big improvement," said Cornell University seismologist Rowena Lohman. "They brought in more information."


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