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Hot and Bothered
One of the most uncertain aspects of energy production at geothermal fields is the potential for the induction of earthquakes from extraction of hot fluids and injection of wastewater back into the subsurface. Brodsky and Lajoie (p. 543, published online 11 July) compared the historical rates of seismicity—after correcting for the occurrence of aftershocks—to operational parameters at the Salton Sea Geothermal Field in southern California. The net volume of fluid extracted and injected was correlated with recent seismicity. However, since the 1980s, when the first plant came online, the rate of earthquakes induced with additional increments of volume injected has decreased.
Abstract
Geothermal power is a growing energy source; however, efforts to increase production are tempered by concern over induced earthquakes. Although increased seismicity commonly accompanies geothermal production, induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters. We show that at the Salton Sea Geothermal Field, the total volume of fluid extracted or injected tracks the long-term evolution of seismicity. After correcting for the aftershock rate, the net fluid volume (extracted-injected) provides the best correlation with seismicity in recent years. We model the background earthquake rate with a linear combination of injection and net production rates that allows us to track the secular development of the field as the number of earthquakes per fluid volume injected decreases over time.
