Injection wells are linked to earthquakes in a handful of states like: Texas, Wyoming, Arkansas, Ohio, and Colorado. Impact Oklahoma reported the largest earthquake connected to a disposal and injection well occurred on November 2011 in Prague, Oklahoma. However, Oklahoma has not responded with significant regulations.
On the other side of the coin, Ohio has taken stronger action banning disposal wells in areas with higher earthquake risks, reviewing seismic risks prior to issuing permits, and requiring operators to install sensors to record and track well data.
A piece by Colorado Matters suggests the EPA is discontinuing the study of hydraulic fracturing effects, even though there is evidence fracking polluted an aquifer in Pavillion, Wyoming.