Strongest Quake in 35 Years Shakes Arkansas Swarm of earthquakes unsettles town By Rob Quinn, Newser Staff Posted Mar 1, 2011 3:22 AM CST 7 comments Comments This seismic chart provided by the Arkansas Geological Survey shows earthquake activity at Woolly Hollow State Park. (AP Photo/Arkansas Geological Survey) (Newser) – Residents of the central Arkansas town of Greenbrier—already unsettled by hundreds of mild quakes over the last 6 months—were shaken by the biggest earthquake to hit the state in 35 years late Sunday night. The 4.7 magnitude quake, which was followed by two smaller ones, didn't cause any major damage or serious injuries but locals say they're getting worried about the increasing severity of the quakes, AP reports. Residents say the earthquake swarm has been doing gradual damage and the cracks in their homes and driveways have been expanding. Scientists are trying to determine whether the quakes are being caused in part by the natural gas industry, which has been pumping salt water into injection wells in the area. A 6-month moratorium on new injection wells in the area was established in January.