This is one of those areas where it makes intuitive sense, but until now we didn't have anything confirming it. Now it appears that in at least one case, fracking can be directly linked to seismic activity.

Salon:

Case in point: last month, the Ohio Department of Natural Resources temporarily suspended drilling at a number of wells in the northeastern part of the state out of concern that it may have been responsible for a series of earthquakes.

Friday, geologists confirmed that yes, fracking was probably responsible. “ODNR geologists believe the sand and water injected into the well during the hydraulic fracturing process may have increased pressure on an unknown micro-fault in the area,” they said in arelease, leading to the 11 minor quakes experienced in March.

This is a big deal, marking the first time exploration of the Marcellus shale, which reaches from Ohio and West Virginia into Pennsylvania and New York, has been linked with seismic activity, according to a seismologist with the U.S. Department of Interior.

It’s also one of the first times in the U.S. that earthquakes have been linked to fracking itself— in the past, Ohio quakes have been linked to wastewater injection wells, which are merely a fracking-related activity, and not inherent to the process. Those earlier quakes, over 100 of which shook Youngstown, Ohio, happened in an area where there were 177 active wastewater injection wells, the Columbus Dispatch explains. But there were none near the recent earthquakes in Mahoning County, leaving fracking as the prime suspect.

With all of the earthquake activity in Chile recently, it might be worth looking at what fracking activity has been taking place there, too. It's an earthquake-prone area, but lately that activity has ticked up to an almost-frenetic pace.