Human-induced Earthquakes

http://earthquake.usgs.gov/research/induced/

Within the central and eastern United States, the number of earthquakes has increased dramatically over the past few years. Between the years 1973–2008, there was an average of 21 earthquakes of magnitude three and larger in the central and eastern United States. This rate jumped to an average of 99 M3+ earthquakes per year in 2009–2013, and the rate continues to rise. In 2014, alone, there were 659 M3 and larger earthquakes . Most of these earthquakes are in the magnitude 3–4 range, large enough to have been felt by many people, yet small enough to rarely cause damage. There were reports of damage from some of the larger events, including the M5.6 Prague, Oklahoma earthquake and the M5.3 Trinidad, Colorado earthquake.

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A team of USGS scientists led by Bill Ellsworth analyzed changes in the rate of earthquake occurrence using large USGS databases of earthquakes recorded since 1970. The increase in seismicity has been found to coincide with the injection of wastewater in deep disposal wells in several locations, including Colorado, Texas, Arkansas, Oklahoma and Ohio. 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.

Hydraulic fracturing, commonly known as “fracking,” does not appear to be linked to the increased rate of magnitude 3 and larger earthquakes.

Although wastewater injection has not yet been linked to large earthquakes (M6+), scientists cannot eliminate the possibility. It does appear that wastewater disposal induced the M5.3 Raton Basin, Colorado earthquake in 2011 as well as the M5.6 quake that struck Prague, Oklahoma in 2011, leading to a few injuries and damage to more than a dozen homes.

The USGS is coordinating with other federal agencies, including the EPA and Department of Energy, to better understand the occurrence of induced seismicity through both internal research and by funding university-based research with a focus on injection-induced earthquakes from wastewater disposal technologies. For instance, USGS and its university partners have deployed seismometers at sites of known or possible injection-induced earthquakes in Arkansas, Colorado, Ohio, Oklahoma and Texas. The USGS is also monitoring seismicity associated with a geologic carbon dioxide sequestration pilot project at Decatur, Illinois, and is working with industry, academia and other government agencies to study seismicity associated with geothermal energy development and production in California and Nevada.

Evidence from some case histories suggests that the magnitude of the largest earthquake tends to increase as the total volume of injected wastewater increases. Injection pressure and rate of injection may also be factors. More research is needed to determine answers to these important questions.