Shake, rattle and roll: Earthquake risk increased for half of US

The US Geological Survey (USGS) is predicting where earthquakes will occur over the next 50 years, how often they will happen and how hard the shaking will be. About half the country has an increased risk of experiencing seismic activity.

The USGS predictions run 50 years because that is the typical lifetime of a building, the agency said in a blog post. During that time, 42 states have a “reasonable chance of experiencing damaging ground shaking from an earthquake,” while 16 states have a “relatively high likelihood” of such a seismic hazard.

The states most likely to have a damaging earthquake are: Alaska, Arkansas, California, Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah, Washington and Wyoming.

The highest risk places have a 2 percent chance of experiencing "very intense shaking" over a 50-year lifespan, USGS project chief Mark Petersen said to the Associated Press. Those with lower hazard ratings would experience less intense swaying measured in gravitational force.

"These maps are refining our views of what the actual shaking is," Petersen said. "Almost any place in the United States can have an earthquake."

That point was brought home by the August 2011 earthquake in Mineral, VA. The magnitude 5.8 quake, whose epicenter was placed at Mineral, Virginia, was felt across the East Coast, with reports of tremors stretching from North Carolina to Rhode Island, New York City to Cleveland and even in Toronto, Ontario, Canada. It was among the largest earthquakes to occur along the Eastern Seaboard since 1897, and helped scientists determine that even larger events are possible. Estimates of earthquake hazards near Charleston, SC, have also gone up due to the assessment of earthquakes in the state, the USGS said.

In California, earthquake hazard extends over a wider area than previously thought. Scientists discovered new faults in the Golden State, increasing the risk of quakes in San Jose, Vallejo and San Diego. At the same time, though, the risk was decreased the risk estimates for Irvine, Santa Barbara and Oakland, although the greater San Francisco Bay area is more likely to experience intense seismic activity than the USGS predicted in 2008 - the last time the maps were updated.

The maps are important for planning for the future, especially when it comes to building codes.

“The standards for seismic safety in building codes are directly based upon USGS assessments of potential ground shaking from earthquakes, and have been for years,” Jim Harris, a member and former chair of the Provisions Update Committee of the Building Seismic Safety Council, said in the USGS blog post. “The committees preparing those standards welcome this updated USGS information as a basis for making decisions and continuing to ensure the most stable and secure construction.”

While hydraulic fracturing - or fracking - has been linked to increased seismic activities in states like Oklahoma, Idaho, Ohio and Texas, the USGS said it is still researching “induced earthquakes,” or those events that “may be associated with human activities such as the disposal of wastewater in deep wells.” (So far this year, nearly 250 small to medium quakes have hit Oklahoma.)

Petersen told AP that the maps sidestep the issue of earthquakes created by injections of wastewater from oil and gas drilling, and those extra quakes weren’t included in the analysis.

“One specific focus for the future is including an additional layer to these earthquake hazard maps to account for recent potentially triggered earthquakes that occur near some wastewater disposal wells,” the USGS said. “Injection-induced earthquakes are challenging to incorporate into hazard models because they may not behave like natural earthquakes and their rates change based on man-made activities.”

Some localities in the US aren’t waiting for government seismologists to confirm the link between quakes and fracking or to add those events to their maps, though. Several places in California, including Beverly Hills and Santa Cruz County, have already banned hydraulic fracturing, and similar bans and moratoriums are being discussed in areas of Texas, Colorado, Massachusetts, New York, Pennsylvania and Ohio.