Chesapeake Energy Corp,the Oklahoma-based firm is the No. 1 driller in Ohio.
Rig Count Interactive Map by Baker Hughes, an energy services company.
Shale Sheet Fracking, a Youngstown Vindicator blog.
The Ohio Environmental Council, a statewide eco-group based in Columbus.
Earthjustice, a national eco-group.
People's Oil and Gas Collaborative-Ohio, a grass-roots group in Northeast Ohio.
Concerned Citizens of Medina County, a grass-roots group.
No Frack Ohio, a Columbus-based grass-roots group.
Fracking: Gas Drilling's Environmental Threat by ProPublica, an online journalism site.
Pipeline, blog from Pittsburgh Post-Gazette on Marcellus shale drilling.
Allegheny Front, environmental public radio for Western Pennsylvania.
Youngstown Vindicator reporter Karl Henkel reported last week that all 12 Mahoning County earthquakes probably had the same epicenter, contrary to original seismic data.
Won-Young Kin of Columbia University's Lamont-Doherty Cooperative Seismic Network said it is likely that all 12 earthquakes were centered near a brine injection well in Youngstown Township.
There was not enough seismic data previously to pin down the epicenters. The original data pinned the epicenter to within a 3-mile radius. The new data tightens that location and puts the quakes closer to the now-closed injection well.
The Ohio Department of Natural Resources in December asked Columbia University for help. The earthquakes remain under state investigation.
Mahoning County has been rocked by a dozen earthquakes since last March. The biggest was a 4.0-magnitude quake on Dec. 31.
The state has temporarily closed the injection well owned by Youngstown's D&L Energy Inc. Five other nearby injection wells also remain closed.
Injection wells are used to dispose of briny waste from drilling natural gas and oil wells. Ohio has 176 other ijection wells.