A new report from the United States Geological Survey (USGS) shows that approximately 7 million people live and work in areas of the central and eastern U.S. (CEUS) with the potential for damaging shaking from induced seismicity. Within a few portions of the CEUS, the chance of damage from all types of earthquakes is similar to that of natural earthquakes in high-hazard areas of California, according to USGS.

This is the first time that USGS maps have identified potential ground-shaking hazards from both human-induced and natural earthquakes. In the past, they identified only natural earthquake hazards.

USGS forecast for damage from natural and induced earthquakes in 2016. Image credit: USGS. “By including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the U.S.,” says Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project.

Induced earthquakes are triggered by human activities, with wastewater disposal the primary cause for recent events in many areas of the CEUS, USGS says. Wastewater from oil and gas production operations can be disposed of by injecting it into deep underground wells, below aquifers that provide drinking water.

"Many questions have been raised about hydraulic fracturing, and USGS studies suggest that this process is only rarely the cause of felt earthquakes," USGS adds.

USGS says the most significant hazards from induced seismicity are in six states, listed in order from highest to lowest potential hazard: Oklahoma, Kansas, Texas, Colorado, New Mexico and Arkansas. Oklahoma and Texas have the largest populations exposed to induced earthquakes.

The new report is intended to be used by both government officials and emergency-response personnel to assess vulnerability and provide safety information to those who are in potential danger, according to USGS. Engineers can use the data to evaluate earthquake safety of buildings, bridges, pipelines and other important structures.

The report notes that the central U.S. has undergone the most dramatic increase in seismicity—both overall and induced—over the past six years. From 1973 to 2008, there was an average of 24 earthquakes of magnitude 3.0 and larger per year. From 2009 to 2015, the rate steadily increased, averaging 318 per year. To date, the largest earthquake located near several active injection wells was a magnitude 5.6 in 2011 near Prague, Oklahoma, USGS says.