t involve hydraulic fracturing, fracking often involves injecting spent
water into the ground, which carries the same risks. In fracking,
water, sand and other substances are injected into a well under high pressure in order to fracture the rock, creating fissures that help natural gas flow out.
There hasn't been much oil extraction on the East Coast, but as fracking takes off in areas like Pennsylvania, the risk of big quakes in the region needs to be considered, Keranen said
http://news.