Did fracking cause the earthquake?

For a long time, people have been pointing out a possible link between deep drilling and earthquakes. So yesterday I wondered the same thing:

According to geologists, it isn’t the fracking itself that is linked to earthquakes, but the re-injection of waste salt water (as much as 3 million gallons per well) deep into rock beds.

Braxton County West Virginia (160 miles from Mineral) has experienced a rash of freak earthquakes (eight in 2010) since fracking operations started there several years ago. According to geologists fracking also caused an outbreak of thousands of minor earthquakes in Arkansas (as many as two dozen in a single day). It’s also linked to freak earthquakes in Texas, western New York, Oklahoma and Blackpool, England (which had never recorded an earthquake before).

Industry scientists deny the link to earthquakes, arguing that energy companies have been fracking for nearly sixty years. However it’s only a dozen years ago that “slick-water fracks” were introduced. This form of fracking uses huge amounts of water mixed with sand and dozens of toxic chemicals like benzene, all of which is injected under extreme pressure to shatter the underground rock reservoir and release gas trapped in the rock pores. Not only does the practice utilize millions of gallons of freshwater per frack (taken from lakes, rivers, or municipal water supplies), the toxic chemicals mixed in the water to make it “slick” endanger groundwater aquifers and threaten to pollute nearby water-wells.

Horizontal drilling and multi-stage fracking (which extend fractures across several kilometres) were introduced in 2004.