The owners of the Three Mile Island and Peach Bottom nuclear plants will be required to take a new look at their plant designs after a study that finds earthquakes are more likely than earlier thought.

Using updated historical data and seismic computer models, the study calculated the likelihood of earthquake-caused ground motions in the eastern and central United States.

The $7 million study was conducted by the U.S. Nuclear Regulatory Commission, the U.S. Department of Energy and the electric industry's Electric Power Research Institute.

The NRC is requiring the owners of 62 nuclear plants in the region to re-evaluate seismic hazards.

The study was nearing completion at the time of the March 2011 earthquake and tsunami that severely damaged three reactors in Japan. Now, the seismic review is part of the lessons learned from that disaster.

The new study replaces seismic source models used by the industry and government since the late 1980s.

The study looked at historical earthquake and geographical data for the region from 1568 to 2008.

The model can be used to calculate the likelihood of various levels of earthquake-caused ground motions.

Although the new study says earthquakes are more likely than previously thought, NRC officials cautioned that that does not mean nuclear plants are more at risk.

Plant operators will combine information from the new model and examine a plant's design and safety features to determine if there are any safety risks or modifications needed.

The NRC will require each utility to share its risk-analysis based on the new information, said Neil Sheehan, an NRC spokesman in King of Prussia.

"It won't be an overnight effort," he said. "We think the plants are safe at present."

The study found that the most severe earthquakes in the future might occur near New Madrid, Mo., and Charleston, S.C.

acrable@lnpnews.com