By Heide Brandes
OKLAHOMA CITY (Reuters) - A warning from U.S. scientists that Oklahoma may be hit by a major earthquake has caused a run on insurance policies for tremors in the heartland state, adding to the woes of residents already in the firing line of devastating tornadoes.
Quakes have typically been infrequent in Oklahoma, yet not unheard of. But in the past year, minor tremors have hit the state hundreds of times, raising worries the big one may be just around the corner.
"The rate of earthquakes in Oklahoma has increased by about 50 percent since October 2013, significantly increasing the chance for a damaging quake in central Oklahoma," the U.S. Geological Survey (USGS) said earlier this week.
Geologists also say that fracking - a controversial technique for extracting natural gas and oil from underground rock deposits - could be one of the causes.
Oklahoma City resident Mark Myers said that after the USGS issued their warning, he called his insurance agent to look into coverage.
"When you see a warning for a major earthquake in Oklahoma, which I understand is pretty rare, it makes you aware of what could happen," Myers said just after speaking to an agent.
Tornadoes have been a persistent concern for Oklahomans, with an average of 50 hitting a year, usually during the March to August season, causing billions of dollars in damage.
But there has also been a lot of shaking, with 183 earthquakes of magnitude 3.0 or greater on the Richter scale occurring in Oklahoma from October 2013 through April 14, the USGS said.
Oklahoma Insurance Commission spokeswoman Kelly Collins said the agency was curious to see if there has been a jump in coverage for earthquakes and did an informal survey.
Three of the top 10 firms in the state responded and said Oklahomans are taking the threat seriously. When the state had a quake with a magnitude of 5.6 in 2011, only about 2 percent to 4 percent of customers had full coverage.
"Now, 12 to 18 percent have that insurance. It's still less than 20 percent of homeowners, but I think this latest warning would catch people's attention," Collins said.
One factor that may be contributing to the quakes appears to be the hydraulic fracturing, or fracking, an energy extraction method that has boosted employment and provided revenue for the financially strapped state.
Water injection used in fracking to break up underground, porous rock formations can increase underground pressures, lubricate faults and cause earthquakes - a process known as injection-induced seismicity, the USGS said in a joint statement with the Oklahoma Geological Survey.
"The recent earthquake rate changes (in Oklahoma) are not due to typical, random fluctuations in natural seismicity rates," they said.
Several energy firms have dismissed the link between fracking and the recent quakes.
There have been two earthquakes that have registered a magnitude of over 5 on the Richter scale in the state since the 1950s. A 1952 quake with a 5.5 magnitude toppled chimneys in Oklahoma City and left a 15 meter crack in the capitol building.
The worries are a stronger quake than that could cause even more damage where many structures are built to withstand tornado winds but do not have specialized protection against strong seismic activity.
Dave Herbert of Midwest City said as long as there is fracking, he will be worried about a damaging quake.
"I took out an insurance policy on my house," said Herbert. "It was clear to me that Oklahoma was not going to take any meaningful action. Too many oil big shots in the state."
(Writing by Jon Herskovitz, editing by G Crosse)