There has been a dramatic increase in seismic activity in the United States in the past ten years, some of which is caused by fracking but much more of which is the result of waste water from traditional oil and gas drilling; this waste water is reinjected into the ground through new wells. You can find out more about how this all works by reading the US Geological Survey's Earthquake Hazards program page on Induced Earthquakes. There's quite a bit of useful information at their site, and it's layed out in a way that is clear and informative.
However, compare the impact of reading that website with watching the video below, which visualizes seismic activity in Oklahoma over the period from 2004 to 2016 in one minute. Watch what happens in the last 20 seconds.