SCEC Award Number 16061 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 graduate student: Yifang Cheng
SCEC Priorities 2f, 2b, 2c SCEC Groups Seismology, FARM
Report Due Date 03/15/2017 Date Report Submitted 03/15/2017
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. Previous analysis of seismicity clustering leads to the unique spatial distribution and characteristics of the “mixture-type” cluster, which is predominately located within active injection areas, differs from the traditional “aftershock-type” or “swarm-type” clusters. Analysis in this report is focused on spectral analysis using a stacking approach to understand the spatial distributions of stress drop, and the relationship with injection/production wells. The results suggest there exist coherent spatial patterns of stress drop distribution, and seismicity characteristics. We also perform relative-stress drop analysis for a tight repeating earthquake cluster. The relative stress drop confirms the variability of stress drop distributions from stacking analysis.
Intellectual Merit The research contributes to integrated understanding of the geomechanical process within the active geothermal field. The analysis of the spatial distributions of earthquake stress drop will provide key information for hazard assessment. The comparison between stacking approach and relative individual pair analysis provide constraints for the reliability and stability of source parameter estimations.
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 has completed her master thesis in summer 2016, and now a PhD student at USC.
Exemplary Figure Figure 3. B-value, cluster-type, and stress drop distributions within the middle cluster. (a) Map view of b-value distributions (for clarity reasons, only events >3 km are plotted), and contour lines of 800°C/km and 400°C/km geothermal gradient. (b) Cross-section view of b-value along DD’ profile (latitude versus depth). For both (a) and (b), events are colored with b-value. (c) Cross-section view of clustering type along DD’ profile (latitude versus depth). Events within clusters are colored according to clustering type, non-clustered events are shown in grey dots. (d) Cross-section view of stress drop variation along DD’ profile (latitude versus depth). Events are colored by the median stress drops of their nearest 10 events. Injections wells are white squares, and productions wells are white triangles. Historic large magnitude events with M_L≥4 since 1981 are plotted by magenta star.