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.
Mahoning County is not the only earthquake hot spot in Ohio.
Washington County in southern Ohio has had four small quakes since October 2010, according to the Youngstown Vindicator.
The quakes ranged from 2.6 to 3.1 in the Marietta area.
Washington County is also home to more brine injection wells to handle drilling waste than any other county in Ohio.
Seismographs will be installed soon in Washington County to study the quakes.
Youngstown has had 11 quakes since March. That includes a 4.0-magnitude quake on Dec. 31.
The experts say all the quakes are centered near an injection well west of downtown Youngstown in Youngstown Township.
D&L Energy, the owner of the injection well, voluntarily closed on Dec. 30 in an agreement with the Ohio Department of Natural Resources.
Brine under pressure can lubricate fault lines deep under ground and promote slippage or small quakes.