Sue Ogrocki, File, Associated Press
In this June 26, 2014 file photo, Austin Holland, research seismologist at the Oklahoma Geological Survey, hangs up a chart depicting earthquake activity at their offices at the University of Oklahoma in Norman, Okla. States where hydraulic fracturing is taking place have seen a surge in seismic activity, raising suspicions that the unconventional drilling method, especially the wells in which the industry disposes of its wastewater, could be to blame.

OKLAHOMA CITY — Two early morning earthquakes rattled residents in central Oklahoma on Tuesday and caused minor damage at local businesses.

The U.S. Geological Survey reports that a magnitude 3.8 earthquake struck about 2:20 a.m. 3 miles northeast of Harrah, a city of about 5,000 people about 20 miles east of Oklahoma City. That was followed nearly two hours later by a magnitude 3.9 temblor 5 miles northeast of the community.

The quakes were strong enough to knock merchandise off the shelves at an Ace Hardware store along with tiles from the ceiling. Store manager Tony Landrith said the falling paint, cleaner and other items along with the tiles caused the security alarm to go off and the police to respond.

When Landrith arrived at the store after the alarm company called him, he and the police discovered "a little bit of everything on every aisle" had been knocked off, he said.

Employees worked throughout the morning and afternoon to clean up. The store opened two hours late, he said.

Earl Burson, Harrah's city manager, said glass windows were shattered at buildings on the city's main street, Church Avenue, and the police department sustained cracks in the wall.

"I'm surprised we had as a little damage as we do," he said. No injuries were reported.

Like Landrith, Burson was woken up by a call after the alarm went off at City Hall after the first quake. After the second quake, alarms started going off throughout the community.

The USGS also reported that a third earthquake struck in north-central Oklahoma Tuesday morning. The magnitude 3.0 earthquake was 5 miles south of Medford at 5 a.m.

Earlier this week, the USGS reported seven small earthquakes shaking 15 to 30 miles northeast of Oklahoma City in a span of 14 hours.

The temblors are part of an increase in earthquakes across Oklahoma, Texas and Kansas that some scientists say could be connected to the oil and gas drilling method known as hydraulic fracturing, and especially the wells in which the industry disposes of its wastewater.

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