SCEC Award Number 12225 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title What is the effect of induced seismicity on tectonic faults?
Investigator(s)
Name Organization
Emily Brodsky University of California, Santa Cruz
Other Participants
SCEC Priorities 2f, 2b, 2c SCEC Groups EFP, WGCEP, SoSAFE
Report Due Date 03/15/2013 Date Report Submitted N/A
Project 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 based on known volumes of fluid injection or any other operational parameter. Here we show that at the flash facilities in the Salton Sea Geothermal Field, the total volume of fluid extracted or injected tracks the long-term evolution of seismicity. However, for recent years net fluid volume (extracted-injected) is better correlated with seismicity. After correcting for the variable aftershock rate, we model the background earthquake rate with a linear combination of injection and net production rate that allows us to track the secular evolution of the field. The number of earthquakes per fluid volume injected decreases gradually over time. This new analysis of induced seismicity provides a template for future evaluation of hazard directly based on measureable, controllable operational quantities.
Intellectual Merit We demonstrated a direct connection between a known forcing (net extraction) and the resultant seismicity rate. This observation sets the stage for quantifying the stresses necessary to trigger earthquakes.
Broader Impacts The seismicity associated with the geothermal power plants in the Salton Sea could potentially trigger a major Southern San Andreas earthquake. Evaluating the likelihood of this triggering and determining the appropriate operational levels to manage the risk is an important public safety goal for SCEC.
Exemplary Figure Figure 3: Seismicity background rate (ยต) over time compared to operational fluid volumes at the Salton Sea Geothermal Field. The seismicity rate curve is identical for each panel (right hand axis, green curve) and the comparison fluid volume (left axis, blue curve) in each case is (a) Production rate, (b) Injection rate and (c) Net Production rate.

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Supplementary Figure 2: Sample seismicity rate and model prediction of the seismicity rate using the observed fluid data and the best-fit linear model of Eq. 2.
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