As more earthquakes shake Oklahoma, state adopts more California-style precautions

After decades of little seismic activity in Oklahoma, earthquakes have become more common in the last several years. And a new study by the U.S. Geological Survey suggests they are here to stay.

From 1975 to 2008, only a handful of magnitude-3.0 earthquakes or greater occurred yearly in Oklahoma. But the report issued last month found that since 2009, more than 200 such quakes have hit the state's midsection. Many have been centered near Oklahoma City, the most populous part of the state.

Scientists are not sure why seismic activity has spiked.

No one has been killed or seriously hurt in the recent quakes, and property damage has been minimal. But more Oklahomans are considering earthquake insurance, and emergency officials have reviewed earthquake-safety manuals used in California.