Swarm of earthquakes bedevils Arkansas

The earth is restless in Arkansas - remarkably so - and no one is quite sure why. Since last September, more than 800 earthquakes have rocked the central Arkansas town of Greenbrier, and residents are becoming "unsettled by the[ir] increasing severity and lack of warning." 1
The Huffington Post reports that

earthquakes ranging in magnitude from 1.8 to 3.8 have rattled the north-central Arkansas cities of Greenbrier and Guy this week, and the cause is unknown.

The U.S. Geological Survey has reported more than 30 earthquakes in the area since Sunday [February 13], including a magnitude 3.8 quake Thursday morning and at least 16 others occurring Wednesday, two of which were magnitude 3.2 and 3.5.

The latest quake to shake the area was

A 4.7-magnitude earthquake that researchers described as the largest in Arkansas in 35 years [...] There were no reports of major damage, though some residents spoke of dislodged screen doors and cracked ceilings. Damage or not, some said this was the longest and scariest quake yet.

While experts are largely at a loss to explain this swarm of earthquakes, some scientists have suggested a connection to natural gas drilling in the area:

Researchers with the Arkansas Geological Survey have pointed out spatial and temporal relationships between the earthquakes and the use of injection wells, which are used to dispose of the wastewater left over from gas drilling. (Researchers see no such correlation between the quakes and the drilling itself, a process called hydraulic fracturing.) While a possible connection is being studied, the Arkansas Oil and Gas Commission has imposed an emergency moratorium on the drilling of new injection wells in the area.

You can read more here. (Map from NYT.)