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The development and operation of Enhanced Geothermal Systems (EGS) can induce earthquakes during fluid injections, posing significant hazards for both local populations and the continued operation of EGS plants. An improved understanding of the interplay between the physical mechanisms affecting geothermal induced seismicity is important for current and future EGS projects. One way to analyze seismicity is with the b-value, which represents the slope of earthquake magnitude frequency distributions. Previous EGS studies suggest a pore-pressure driven induced seismicity model where spatially – the b-value is high near the injection point and temporally – the b-value decreases during later stages of injection. We evaluate the pore-pressure driven model by comparing the spatiotemporal b-value evolutions of nine different EGS induced seismicity scenarios including Basel and FORGE, along with injections from Soultzsous-Forêts and Cooper Basin. In our spatiotemporal analyses, we find that a majority of examined sequences have a period where the distal b-value is significantly higher than the b-value near the injection point. These sequences indicate that the pore-pressure driven model is inadequate for describing spatiotemporal b-value evolution, and that additional physical mechanisms, like aseismic slip, could have significant effects on EGS induced seismicity. Further characterization of the b-value in EGS induced seismicity sequences provides an opportunity to better constrain the degrees to which different physical mechanisms influence seismicity.
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This content will become publicly available on March 1, 2026
Characterizing hydraulic fracture formation during enhanced geothermal system experiments using coda waves
Seismic waves are valuable for detecting structural variations in the subsurface and can be used to investigate enhanced geothermal systems (EGS). Classic methods, like seismic reflection, struggle to resolve these effects when the perturbations are confined to small volumes of rock, thus requiring other methods. Multiply scattered waves are better suited to resolving small structural changes due to their cumulative sensitivity acquired by their longer propagation times within the medium. With the growing focus on renewable energy production, an improved characterization of fracture network geometry created during EGS stimulations is crucial. In this study, we leverage coda from waveforms generated by a continuous active seismic source to investigate fracture development during the EGS Collab Experiment 1 at the Sanford Underground Research Facility (SURF). By measuring waveform decorrelation, we use scattering cross-section density as a proxy for the induced hydraulic fractures. Our approach implements a genetic algorithm to invert for scattering distributions, posing the problem as a nonlinear optimization. We also constrain the scattering perturbations to plane structures, enforcing realistic sparsity in fracture patterns that is otherwise poorly resolved in linearized approaches. Results from synthetic examples demonstrate the effectiveness of this approach in recovering scattering density, highlighting its potential to complement methods that utilize induced seismicity for improving characterization of fracture networks in enhanced geothermal reservoirs.
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- Award ID(s):
- 2113367
- PAR ID:
- 10614782
- Publisher / Repository:
- SEG
- Date Published:
- Journal Name:
- The Leading Edge
- Volume:
- 44
- Issue:
- 3
- ISSN:
- 1070-485X
- Page Range / eLocation ID:
- 163 to 169
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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