The U.S. Geological Survey (USGS) reports that human-induced seismicity may be the cause of increased domestic earthquake activity over the past several years. The federal agency released numbers indicating that the U.S. averaged around 20 earthquakes of magnitude 3.0 or larger per year between 1970 and 2000. That number, however, jumped to more than 100 earthquakes per year between 2010 and 2013, with more than 450 earthquakes greater than magnitude-3.0 during that four-year period.

USGS scientists examined several factors when deducing whether the greater number of earthquakes were a result of natural or man-made causes, including local geologic conditions and the presence of waterwater injection sites. They concluded that the increase in seismicity at some locations coincides with wastewater injection in deep disposal wells.

Sources: U.S. Geological Survey