Understanding induced seismicity

Fluid injection–induced seismicity has become increasingly widespread in oil- and gas-producing areas of the United States (1–3) and western Canada. It has shelved deep geothermal energy projects in Switzerland and the United States (4), and its effects are especially acute in Oklahoma, where seismic hazard is now approaching the tectonic levels of parts of California. Unclear in the highly charged debate over expansion of shale gas recovery has been the role of hydraulic fracturing (fracking) in causing increased levels of induced seismicity. Opponents to shale gas development have vilified fracking as directly responsible for this increase in seismicity. However, this purported causal link is not substantiated; the predominant view is that triggering in the midwestern United States is principally a result of massive reinjection of energy-coproduced wastewaters. On page 1406 of this issue, Bao and Eaton (5) identify at least one example of seismicity developed from hydraulic fracturing for shale gas in the Alberta Basin.