PRAGUE, Okla. - It's become a predictable routine at Matt Pryor's insurance agency: An earthquake rumbles through Oklahoma, rattling dishes and nerves. Then the phones light up with calls and text messages from desperate residents asking if it's too late to buy a policy to cover any damage.

Business at Pryor's Oklahoma City office has been brisk after a pair of temblors that struck recently near Edmond, a bedroom community where residents are more accustomed to watching the sky for tornadoes than bracing for the earth to move.

Oklahoma is crisscrossed with fault lines that generate frequent small earthquakes, most too weak to be felt. But after decades of limited seismic activity in this region, 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.

"The increased hazard has important implications for residents and businesses in the area," cautioned the report, released in October.

Pryor has witnessed the rapid change in thinking.

"It used to be, 'Do I need earthquake coverage?' Now it's changed to, 'How much insurance do I need?' " Pryor said. "I never thought it would be a concern, but anything can happen here."

From 1975 to 2008, only a handful of magnitude-3.0 earthquakes or greater occurred yearly in Oklahoma. But the average grew to around 40 annual earthquakes from 2009 to 2013, seismologists said in the report on the uptick of quake activity.

Since 2009, more than 200 magnitude-3.0 or greater earthquakes have hit the state's midsection, according to the Geological Survey. Many have been centered near Oklahoma City, the most populous part of the state.

Scientists are not sure why seismic activity has spiked, but they are studying the phenomenon. One theory is that the shaking could be related to wastewater from oil and gas drilling that is often discarded by injecting it deep into underground wells.