"...according to the Colorado Oil and Gas Conservation Commission, which tested Markham's water in 2008, there were "no indications of oil & gas related impacts to water well." Instead the investigation found that the methane was "biogenic" in nature, meaning it was naturally occurring and that his water well was drilled into a natural gas pocket." http://cogcc.state.co.us/library/GASLAND%20DOC.pdf
Earthquakes? Likely... UK firm says shale fracking caused earthquakes | Reuters
However, there are over 1 million naturally occuring earthquakes each year.