"Hydraulic fracturing in a well for shale gas development, which involves injection of fluids to fracture the shale and release the gas up the well, has been confirmed as the cause for small felt seismic events at one location in the world, " the report states.
Hydraulic fracturing, or fracking, is under widespread development in the United States, fueling a natural gas supply boom, with an EPA review of its environmental safety underway.