SCEC Award Number 15024 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Exploring Temporal Variability in Seismic Velocity at the Salton Sea Geothermal Field and its Implication for Induced Seismicity
Investigator(s)
Name Organization
Taka'aki Taira University of California, Berkeley
Other Participants Potential number of students at UC Berkeley: 2 (Avinash Nayak and Qingkai Kong)
SCEC Priorities 2f, 2c, 2d SCEC Groups Seismology, SDOT, CSEP
Report Due Date 03/15/2016 Date Report Submitted 11/09/2016
Project Abstract
 We search for velocity changes associated with activities of the geothermal energy development at the Salton Sea Geothermal Field. The noise cross-correlation functions (NCFs) are computed for ~6 years of continuous three-component seismic data (December 2007 through January 2014) collected at 8 sites from the CalEnergy network. Velocity changes (dv/v) are obtained by measuring time delay between 5-day stacks of NCFs and the reference NCF (average over the entire 6 year period). The time evolution of dv/v exhibits two types of velocity changes. The first type of velocity change is sudden reductions and the other one is a long-term increase. A notable velocity drop is observed in the beginning of April 2010. The onset time of this temporal reduction is correlated with the occurrence of the 4 April 2010 Mw 7.2 El Mayor-Cucapah earthquake. The level of velocity reduction is gradually increased with decrease of the frequency. The largest reduction (0.25%) is observed in the frequency band, 0.5-2.0 Hz. Assuming coda of NCFs are mainly composed of scattered surface waves, the dv/v change was likely occurred in a depth of ~1.0 km depth. The second type of velocity change is a long-term velocity increase. As with the sudden velocity reductions associated with earthquakes, the long-term increase in velocity displays clear frequency dependence. The larger velocity increase was identified in lower frequency bands. An increase in velocity of ~0.3% was found in the 0.5-2.0 Hz band during a 6-year period, which corresponds a 0.05%/year increase in velocity.
Intellectual Merit This project relates to several SCEC objectives related to the induced seismicity and will advance our knowledge of the behavior in the geothermal reservoir dynamics at the Salton Sea Geothermal Field. In particular, our time history of seismic velocity change provides additional insights into the relationships between the geothermal operation and the long-term velocity change at the Salton Sea Geothermal Field.
Broader Impacts This project documents the temporal variability of seismic velocity at the Salton Sea Geothermal Field by systematically analyzing ~6 year of continuous seismic data with seismic interferometry. A student involved in this project is actively participating in the SCEC annual meeting with the travel support from this project.
Exemplary Figure Figure 2 of the Technical Report. Figure caption (from the report): Temporal evolution of seismic velocity (dv/v) with five different frequency bands. EMC and BS represent the 2010 Mw 7.2 El Mayor-Cucapah earthquake and 2012 Brawley seismic swarm.