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, or hydraulic fracturing, is a controversial process for extracting oil and natural gas from the ground It's spreading across the US despite there being a lot of concerns about it. A typical oil well is built straight down and pumps out all of the oil and natural gas that is deep down in the earth. But after continual use, these oil wells can start coming up dry. So fracking involves angling the drill horizontally into the rock layer and then blasting water at high pressures (this is why its called hydraulic) to release natural gas.