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.
DEFINITION of 'Fracking'. A slang term for hydraulic fracturing. Fracking refers to the procedure of creating fractures in rocks and rock formations by injecting fluid into cracks to force them further open. The larger fissures allow more oil and gas to flow out of the formation and into the wellbore, from where it can be extracted. Fracking has resulted in many oil and gas wells attaining a state of economic viability, due to the level of extraction that can be reached.