Humans "Inducing" Earthquakes During Energy Exploration, USGS Report Says

Human activities that inject fluids into the ground, such as natural gas extractions and geothermal energy production, are the cause of many earthquakes in the United States, including a destructive 5.6-magnitude tremor in Oklahoma in 2011, according to new research published in the journal Science.

While the continental United States experiences small earthquakes each day, a recent study by the U.S. Geological Survey found that the annual number of earthquakes recorded at magnitude 3.0 or greater in the central and eastern regions of the country have increased tenfold over the last decade, and researchers suggest man-made activity is causing trembling, at least partially.

"USGS scientists have found that at some locations the increase in seismicity coincides with the injection of wastewater in deep disposal wells. Much of this wastewater is a byproduct of oil and gas production and is routinely disposed of by injection into wells specifically designed and approved for this purpose," the agency wrote on its website.

This so-called wastewater is a polluted byproduct from these energy exploration operations. It is considered a contaminant and must be disposed of in a way that will not pollute freshwater sources. Injecting it deep in to the ground is an accepted disposal method.

The researchers found that when wastewater disposal occurs near faults and other underground conditions are right, earthquakes are more likely to occur. For instance, if engineers raise the water pressure inside a fault, it can trigger an earthquake. If conditions are right, an earthquake can be generated in a fault even if it has not moved in millions of years, the USGS reports.

Many have suspected the controversial process of hydraulic fracturing, or fracking -- which uses high-pressure fluids to shatter rocks and release trapped gas -- as a contributor to earthquakes. But lead researcher William Ellsworth, a seismologist for the USGS, says that the process has never produced an earthquake larger than magnitude 3.6, and that wastewater disposal is what has driven the increase in bigger earthquakes.

"Clearly it is happening. Earthquakes have been happening in some unusual parts of the United States," Ellsworth said. "At this point, we do not know if all or just some part of that increase is attributable to industrial activities like wastewater injection."

Nobody has been killed as a result of these man-made earthquakes, the strongest of which was the 5.6 magnitude Oklahoma quake. But the quakes have caused injury and structural damage.

Ellsworth and his colleagues' study is published in the journal Science.