Cliff Frohlich told scientists gathered in Morgantown for a National Research Council forum in Morgantown, W. Va., that when quakes do happen, they're typically linked to the disposal of drilling fluids in underground injection wells.
And Frohlich says the vast majority of injection wells don't cause quakes, either.
Frohlich cited six earthquakes since 2008 in Texas, Arkansas, Colorado, Ohio and Oklahoma, ranging from magnitude 3.3 to magnitude 5.7.
He says that shows human-caused earthquakes are geographically widespread and geologically diverse, but rare considering the amount of petroleum produced and the amount of waste being disposed of.
Frohlich says it's still unclear why some injection wells cause earthquakes and others don't.
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.