SCEC Award Number 16071 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Effect of geothermal operations on earthquake source processes in the Coso geothermal field using borehole stations and improved velocity model
Name Organization
Xiaowei Chen University of Oklahoma Qiong Zhang California Institute of Technology Robert Clayton California Institute of Technology
Other Participants graduate student: Yan Qin
SCEC Priorities 2f, 2b, 2c SCEC Groups Seismology, FARM
Report Due Date 03/15/2017 Date Report Submitted 03/15/2017
Project Abstract
Geothermal operations can alter the stress field compared to the expected tectonic stress regime, such as the Geysers geothermal field [Martínez-garzón et al., 2014]. Within the Coso region, we also find systematically different stress regimes inside and outside the active geothermal field (see Figure 1b). Such differences within similar tectonic settings may result in different fault strength levels as predicted by Anderson’s faulting theory, and cause differences in earthquake stress drop. In this report, we primarily focused on analysis of earthquake clustering behaviors to understand whether earthquake source behave differently inside and outside the geothermal field. Our analysis suggests that clusters driven by diffusive migration primarily occur outside the geothermal field, suggesting lack of differential pore pressure due to continuous flushing of the fracture network inside the geothermal field. These results support the observation of lack of dynamic triggering inside the geothermal field. We also performed preliminary analysis of earthquake source spectra using modified stacking approach applying to single stations for two compact clusters – the Coso geothermal field, and a cluster in the Rose Valley. The preliminary spectral analysis shows that there is no systematic difference in the stress drop between induced seismicity and tectonic seismicity for the two clusters.
Intellectual Merit The research contributes to integrated understanding of the earthquake source process inside and outside the geothermal field. The finding of lack of fluid-drive swarms correlating with lack of dynamically triggered earthquakes inside the geothermal field contributes to the mechanisms of dynamic triggering. The comparison of source parameters for directly induced events and natural tectonic events are of significant interest with increased induced seismicity in central US.
Broader Impacts The project results are beneficial for learning earthquake hazards, risks and earthquake physics. The project contributed to the training and education of students at OU. Graduate student Yan Qin contributed to the study of dynamic triggering led by PI Qiong Zhang at Caltech, which is published on GRL in 2017 Zhang et al., [2017]. Undergraduate student Abraham Wallace at OU received training in analysis of seismicity.

Exemplary Figure Figure 1. Spatial distribution and migration patterns of swarms. (a) Map of three types of earthquake swarms analyzed from the 1981–2011 relocation catalog. Each swarm contains more than 20 events. The swarms showing migration with hydraulic diffusion are denoted by blue circles. Squares and crosses denote swarms with linear migration and no obvious migration, respectively. The red and blue background colors are the same as in Figure . (b) Stacked time‐distance plot of 14 swarms fitting to diffusion migration (blue circles in Figure a). The events in one swarm are denoted by the same color. The time is normalized by ti, the maximum time for each swarm. The distance is normalized by
(Di is the hydraulic diffusivity for each swarm). The dashed line shows the migration front with the median diffusivity of 0.5 m2/s.