Is fracking likely to produce earthquakes?
It's not too too likely, but it can happen. A few earthquakes have either been attributed to fracking, or the wastewater produced from fracking.

According to the USGS (for more information, visit that page):


  Many questions have been raised about whether hydraulic fracturing —
  commonly known as “fracking”— is responsible for the recent increase
  of earthquakes. USGS’s studies suggest that the actual hydraulic
  fracturing process is only very rarely the direct cause of felt
  earthquakes. While hydraulic fracturing works by making thousands of
  extremely small “microearthquakes,” they are, with just a few
  exceptions, too small to be felt; none have been large enough to cause
  structural damage. As noted previously, underground disposal of
  wastewater co-produced with oil and gas, enabled by hydraulic
  fracturing operations, has been linked to induced earthquakes.


So, indeed, the disposal of wastewater has been linked to earthquakes.

This study in Geology also came to the same conclusion that the wastewater of fracking caused earthquakes.

An additional study produced by Ohio geologists concluded that a few small earthquakes were due to fracking. I do wonder exactly what they concluded, but the news story doesn't say. It does say this, but it doesn't say exact what this study was, either:


  A U.S. government-funded report released in 2012 found that two worldwide instances of shaking can be attributed to actual extraction of oil and gas, as opposed to wastewater disposal in the ground — a magnitude-2.8 quake in Oklahoma and a magnitude-2.3 quake in England. Both were in 2011.