Can shale fracking be responsible for Ohio's recent seismic activity?

The area of Youngstown, Ohio had never experienced earthquakes, up until 2011 where about 109 minor seismic events were recorded, initiating relative research on behalf of the Geophysical Research-Solid Earth, indicating how this could be the result of shale fracking activity in the area. 

Wastewater from oil and gas production is usually injected into permeable rock formations under pressure, in many states across the U.S. The particular process, referred to as fracking, is performed through wells, and has been held responsible for the onset of the Youngstown Ohio seismic activity. More specifically, in December 2010, the Northstar 1 well, built to pump wastewater produced by fracking, was blamed for the occurrence of 109 tremors, the strongest having a magnitude of 3.9. It was observed that the onset, stop as well as temporary drops in seismic activity were somehow connected to the pumping activity of the well. The observed drop in seismic activity dropped during public holiday seasons, such as Labor Day, Thanksgiving as well as periods, when injection was temporarily stopped. Scientists found that the water pumped into the rock formations increased pressures, causing old faults to slip relatively to each other and generate minor seismic events. Provided the above evidence, Northstar 1 was permanently closed in 2012 and new wells were prohibited within a zone of 5miles from the spot. 

However, an oil well undergoing hydraulic fracking in the town of Poland, near the Pennsylvania border, is suspected to have caused two new earthquakes of magnitude 2.6 and 3.0 in the area, on Monday March 10th 2014. The area is located only 15 miles southeast of Youngstown. Hilcorp's Energy spokesman said that one of the affected wells had been undergoing fracking to release oil and gas. Wells were in different stages of construction, reaching a depth of about 1.5 miles and extending horizontally for about a mile inside the shale. According to the United States Geological Survey, the first earthquake occurred in the same approximate depth.