The range of 60-70 decibels sound pressure level is about as loud as normal conversation in 1 meter distance. The distance from the ears to the sound source is very important to the value of the SPL. Scroll down to related links and look at Table of Sound Pressure Levels.
1 Primarily, during the fracking process:  [Earthquakes] were caused by fluid injection during hydraulic fracturing in proximity to pre-existing faults.. 2  Secondarily, via the disposal of fracking wastewater via underground injection.
Some earthquakes have been linked to hydraulic fracturing, or fracking, but for the most part, the Oklahoma earthquakes are linked to wastewater wells, Williams said. Geophysicists have not been able to gather data to pin down the certain set of wastewater wells that are causing the earthquake problem, but they're hopeful to learn more about the problematic wells in the future.