SCEC Award Number 11040
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title A 3D Velocity Model for the Brawley Seismic Zone from Combined Active and Passive Seismic Data
Investigator(s)
Name Organization
Jeffrey McGuire Woods Hole Oceanographic Institution
Other Participants
SCEC Priorities A4, A6 SCEC Groups Seismology, FARM
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 We are developing a high resolution 3D velocity model for the northern part of the Brawley Seismic Zone beneath the Salton Sea Geothermal Field. This is one of the most seismically active zones in California and includes newly mapped high slip-rate faults (> 1cm/yr) that were not recognized until the last few years owing to the lack of a clear surface trace. Our study will identify the fault systems responsible for the high-rate of seismicity by improving the resolution of absolute earthquake locations and connecting them with faults observed in recent seismic reflection studies. We have succesfully merged data from multiple active source experiments with earthquake data recorded by the local borehole network. The combined relocated seismicity shows a strong correlation with the zone of metamorphic alteration of Salton Trough sediments.
Intellectual Merit Our work is seeking to reconcile rock mechanics experiments with seismicity in an unusual enviorment. The very high temperatures (>350C) reached at shallow depths (1-2 km) in the Salton Trough geothermal field should prevent earthquakes in the quartz sediments there. However, it is one of the most seismically active areas of CA. The seismic velocity anomalies likely result from alteration of the sediments into more competent rocks capable of supporting rupture at high temperature.
Broader Impacts We are developing an improved understanding of a high-slip rate (>1 cm/yr) fault system that is connected to one of the largest alternative energy production operations in the country.
Exemplary Figure Figure 5 shows the correspondence between earthquake locations and high seismic velocities that result from metamorphic alterantion of the Salton Trough sediments.