SCEC Award Number 15062 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Effect of geothermal operations on earthquake source processes in the Salton Sea geothermal field
Investigator(s)
Name Organization
Xiaowei Chen University of Oklahoma
Other Participants
SCEC Priorities 2f, 2b, 2c SCEC Groups Seismology, FARM
Report Due Date 03/15/2016 Date Report Submitted 11/13/2016
Project Abstract
 The borehole network operated by CalEnergy provides high quality dataset for the microearthquakes in the Salton Sea geothermal region. The network was open to public from 2008 to early 2014, which recorded over 7000 earthquakes in the geothermal field. We obtain high-resolution earthquake locations for the Salton Sea Geothermal field with seismic data recorded by a local borehole network and a 3D velocity model. Spatially and temporally isolated earthquake clusters are identified and classified into aftershock-type, swarm-type, and mixture-type, based on the relative timing of largest earthquakes and moment-release history. Analysis of the spatial distribution of clustering type and b-value variations reveals systematic spatial variations of seismicity characteristics that are related to the proximity to geothermal reservoir. Areas farther from injection wells tend to have low b-value, frequent larger earthquakes (M≥2.5), swarm and aftershock-type clusters; likely suggest faults activated by aseismic stress loading or coupled fluid flow. A sphere-shaped microearthquake cloud is located directly beneath a group of injection wells, and is characterized by high b-value, lack of large earthquakes, and short-duration, mixture-type clustering. Probabilities of M ≥ 3 earthquakes are estimated based on spatial-varying magnitude frequency distributions, and exhibit overall low probability within the geothermal reservoir, with the exception of a high-probability zone adjacent to the main central fault. We interpret the spatial variation of seismicity as the result of interaction among fluid circulation, fracture network related to intrusive body and tectonic faulting. The spatial patterns in seismicity characteristics would help us to understand earthquake hazards associated with geothermal operations.
Intellectual Merit The research contributes to integrated understanding of the geomechanical process within the active geothermal field. The new findings of systematic spatial variations of seismicity characteristics is important for distinguishing induced versus natural events, and earthquake hazard assessment.
Broader Impacts The project results are beneficial for learning earthquake hazards, risks and earthquake physics. Due to the recent increase in earthquakes in central US, the students at the University of Oklahoma are interested in learning more about induced seismicity, and enrolled in my seminar on “induced seismicity”. Student Yifang Cheng at OU has been working on this project since Jan 2015. She is expected to complete her master thesis in summer 2016. She has completed the seismicity analysis, presented her result at the SEG and AGU annual meetings in 2015, and is working on the spectral analysis.
Exemplary Figure Figure 3. Map (a) and cross-section (black line) (b) view of injection well (white square), production well (white triangle), background events (gray dot) and clustered events belonging to regular aftershock (blue), swarm (green), mixture (red) in Salton Sea geothermal field and historic large magnitude events with M≥4.0 since 1981 (magenta star). Events with M≥2.5 in our study period are plotted by larger circle. The box is the chosen area for detailed discussion.
Credit to Yifang Cheng