The number of earthquakes has changed over the past several years within central and eastern United States. Nearly 450 earthquakes scale 3.0 and higher happened in the four years from 2010-2013, an average of over 100 each year, compared with an average rate of 20 earthquakes each year noticed from 1970-2000. 

Seismicity of the coterminous United States and surrounding areas, 2009–2012. Black spots represent earthquakes with a magnitude ≥ 3.0 are shown; bigger spots represent events with a magnitude ≥ 4.0. Background colors show earthquake threat levels from the US National Seismic Hazard Map (NSHM).

Credit:USGS

This changed magnitude in earthquakes reminds two important questions: Are they natural, or human induced earthquake? In addition, what should be done in the future as we deal with the causes and effects of these actions to decrease associated risks? USGS researchers have been examining the changes in earthquakes as well as the likely causes, and they have some answers.