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.
Fracking is the process of drilling down into the earth before a high-pressure water mixture is directed at the rock to release the gas inside.Water, sand and chemicals are injected into the rock at high pressure which allows the gas to flow out to the head of the well.The process is carried out vertically or, more commonly, by drilling horizontally to the rock layer.ater, sand and chemicals are injected into the rock at high pressure which allows the gas to flow out to the head of the well. The process is carried out vertically or, more commonly, by drilling horizontally to the rock layer.