Human-caused earthquakes or "induced quakes" put about 7 million Americans at risk, a new report from the U.S. Geological Survey (USGS) found. These induced quakes form when wastewater, which is a byproduct of energy drilling, is injected into deep wells.

Many oil and gas companies started to adopt a new method called hydraulic fracturing or fracking. In this process, the subsurface shale rock is shattered to release the gas and oil. This method produces the chemical-laced wastewater that the industry pumps deep underground for disposal.

"By including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the U.S.," said Mark Petersen, USGS National Seismic Hazard Mapping Project chief.

The USGS report released a map of earthquake hazard areas in the country, including both natural and human-caused quakes. The report found that the central United States is now an earthquake prone area equivalent to California's unstable landscape.

Areas that carry the highest human-caused quakes include Kansas, Oklahoma, Arkansas, Texas, Colorado, Ohio, Alabama and New Mexico. Most of the quakes remain in the magnitude 3 range. However, some could become more intense, including Oklahoma's 2011 magnitude 5.6 earthquake, which was traced to the injection of wastewater.

While there is no upper limit on the induced earthquakes magnitude yet, Oklahoma experienced prehistoric earthquakes that were up to magnitude 7.

Other experts, including USGS seismologist George Choy who studies human-caused earthquakes, were quick to warn about blaming hydraulic fracturing as the root cause of these earthquakes. Many injection wells are not linked to the earthquakes, however, some have been linked in past published studies.

"In general, fracking is still not the major culprit for earthquakes. It's certainly not completely innocent, but we have to worry about regular gas and oil explorations," said Choy who was not part of the USGS's published report.

Previous USGS earthquake maps did not include human-caused events. The new color-coded USGS map serves as a notice to the general population living in recently added earthquake-prone areas to prepare for any ground shaking events wherein Oklahoma is even redder than the unstable terrains of California.

Photo: Martin Luff | Flickr

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