A new study by the U.S. Geological Survey said expanded drilling for oil and gas has led to a disturbing rise in the number of small earthquakes in areas not usually prone to seismic activity.

The study released Thursday examined 17 areas within eight states in the central and eastern parts of the U.S. that are newly designated as being vulnerable to earthquakes. Traditionally, earthquakes have occurred most frequently on the U.S. West Coast.

The most dramatic rise has occurred in the central state of Oklahoma. Before 2008, around the time oil and gas drilling began to rapidly expand there, Oklahoma saw just one or two quakes per year of greater than 3.0-magnitude. It now sees one or two such quakes per day.

The earthquakes are believed to be related to an oil and gas drilling technique known as hydraulic fracturing, or fracking, which involves pumping high-pressure water, sand and chemicals into rock formations deep underground.

Fracturing the rock releases oil and gas trapped inside. It also creates a large amount of wastewater, which is sometimes injected back underground.

Underground disposal wells

Experts said that final step of pumping the water back into underground disposal wells can help activate dormant faults, which is leading to a rise in the small tremors.

Fracking has long been questioned by environmental rights activists, not only because it may be causing earthquakes, but because they say it also pollutes nearby groundwater and leaks harmful fumes into the atmosphere.

Supporters of fracking say the drilling process has helped the U.S. economy and reduced American dependence on foreign oil. Oil and gas companies have also defended fracking, saying there is no definitive proof it is linked to earthquakes.

An increasing number of experts are suggesting otherwise, however. Earlier this week, the state of Oklahoma released a report acknowledging for the first time that it is “very likely” the recent rise in earthquakes was caused by the disposal of oil and gas drilling wastewater.

Most of the allegedly manmade earthquakes have been relatively small and have done little damage. But experts warn there is no guarantee the temblors will not increase the chance for much larger seismic events.

The USGS study stressed that predicting when and where these earthquakes may occur is challenging. Since earthquakes do not appear to occur uniformly near every disposal well, it said further study is needed to help better assess future patterns and trends.
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