A new independent study concludes that fracking is not likely to cause earthquakes, as fracking opponents frequently allege, but there is a greater likelihood of tremors from waste water injection after the well bores have been fracked.

The U.S. Department of Energy-sponsored study was issued Friday by the nonprofit National Research Council. The 239-page study concludes that the factor most directly correlated with man-made earthquakes is the imbalance of fluid removed from the earth versus fluids pumped underground.

The study comes on the heels of the N.C. House of Representatives passing legislation last week that would legalize fracking in this state within several years. The state Senate will take up the measure this week and is expected to approve it. Meanwhile, Gov. Bev Perdue has remained conspicuously silent as to whether she'll veto the legislation.

Scientists have known since the 1920s that pumping fluids into or out of the earth has the potential to induce seismic events. One of the arguments opponents cited against the N.C. energy bill debated last week was the increased likelihood of of tremors and quakes associated with fracking, also known as hydrofracking.

Progress Energy's Shearon Harris nuclear plant in Wake County was one of a dozen nationwide to declare an unusual event after Tuesday's earthquake, but plant operators barely felt the tremor and found nothing amiss after a thorough inspection.

State and local officials have evacuation plans in place for a major emergency, but the 5.8 magnitude earthquake was not felt by many of the engineers and technicians inside the Shearon Harris plant, said Progress spokeswoman Julia Milstead.

Plant officials declared an "unusual event" at 2:06 p.m. on Monday, following the Nuclear Regulatory Commission's criteria for ranking emergencies. An unusual event is the lowest of four emergency levels, and even so, it met only two of the the NRC's three criteria.

The seismic tremors were not strong enough to trigger the plant's earthquake monitors, even though the temblor was felt by some at the plant's administrative offices and shook up people throughout the Triangle.