geothermal induced seismicity: what links source mechanics ... · geothermal induced seismicity:...
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Geothermal induced seismicity: What links source mechanics and event magnitudes to
faulting regimes and injection rates?
Patricia Martínez-Garzón, Grzegorz Kwiatek, Marco Bohnhoff, Stephan Bentz, Georg Dresen
2nd Schatzalp Workshop on Induced Seismicity, 2017 1/13
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Motivation
Main Goal:
• Non Double-Couple (NDC) components describe more accurately the seismic deformation
• Identification of tensile openings allow for monitoring of the desired permeability enhancement in EGS
2/13
• NDC are difficult to detect!
Analysis of large number of MTs to investigate earthquake source-types in relation with the local state of stress and the hydraulic activities nearby
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2nd Schatzalp Workshop on Induced Seismicity, 2017
The NW Geysers geothermal field
• ≈ 4000 EQ/yr since 1960s MW (1.3 – 4.8)
• Mechanisms:a) Thermal fracturingb) Small pressure changes
3/13
SHMax
• Selected area:-2 injection wells- 869 MTs MW [0.8 3.5]- Input data manually processed
Martínez-Garzón et al., 2017
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2nd Schatzalp Workshop on Induced Seismicity, 2017
HybridMT moment tensor calculation
4/13
Gij=Gi
Gij=Gi
Iterative refinement of MTs by removing path effects and correcting for wrong sensor gain
Kwiatek et al., 2016
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Uncertainty assesment and results
5/13
San Andreas (movie)
200 MTs solutions per event perturbing: - P amplitudes Noise- Takeoff angles V model- Polarities Pick errors
Overall NDC uncertainty: ±7%
%𝐼𝑆𝑂 + %𝐶𝐿𝑉𝐷 > 25%for 65% of the MTs
68% with + %ISO & %CLVD15% with - %ISO & %CLVD
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Source types and faulting kinematics
6/13
- Normal faulting: tensile opening
- Reverse faulting: fracture closing
- Strike-slip faulting: DC ruptures
(most compressional)
(least compressional)
Frohlich, 1991
Faulting kinematics:
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Source types and magnitudes
7/13
0.9 < 𝑀𝑊 < 1.6𝐼𝑆𝑂 ≈ 16%, 𝐶𝐿𝑉𝐷 ≈ 13%
2 < 𝑀𝑊 < 2.5𝐼𝑆𝑂 ≈ 3%, 𝐶𝐿𝑉𝐷 ≈ 6%
2.6 < 𝑀𝑊 < 3𝐼𝑆𝑂 ≈ −10%, 𝐶𝐿𝑉𝐷 ≈ −6%
Scholz, 2015
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2nd Schatzalp Workshop on Induced Seismicity, 2017
+ ISO and injection rates
8/13
- Increases during high injection rate periods
- Enhanced at smaller distances from open-hole sections
- Long-term increase
- Related to pore pressure increase?
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2nd Schatzalp Workshop on Induced Seismicity, 2017
+ CLVD and injection activity
9/13
- No clear relation with injection rate- Decreasing with distance from open-
hole sections- Long-term decrease
- A Enhanced damage around open-hole sections ?
- B Multiple events occurring in conjugate faults ?
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2nd Schatzalp Workshop on Induced Seismicity, 2017
NDC components and seismic velocity
10/13
κ = 4
3
%𝐼𝑆𝑂
%𝐶𝐿𝑉𝐷−
1
2=
λ
𝜇=
𝑉𝑃2−𝑉𝑆
2
𝑉𝑆2
- During high injection, the elastic fault properties are different
- The 𝑉𝑃𝑉𝑆 ratio is increasing
(as observed for the whole field)
Gritto and Jarpe, 2014
The Geysers (whole field)
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2nd Schatzalp Workshop on Induced Seismicity, 2017
MTs of M>2 events at the Salton Sea
11/13
- MTs of 80 events M > 2 with local borehole data
- NDC components decreasing with distance from well
- NF near the wells, SS / RF at greater distance
See S. Bentz et al., Poster P1 – 01 (Thu)
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Summary of results
12/13
Analysis of 869 moment tensors from NW The Geysers geothermal field
Source types dependent on local stressstate: Tensile opening at low diff. stress(NF), crack closing at high diff. stress (RF)
Source-types related to EQ magnitudes:Tensile opening at lower magnitudes andcrack closing at larger magnitudes
Volumetric (ISO) components moreresponsive than CLVD to temporal changes ininjection rates
Larger NDC components near open-holesections, suggesting their link with hydraulicoperations
Sourcetypes
Magnitudes
Faulting regime
Injection rates
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Thank you for your attention !
I acknowledge Helmholtz Postdoc Programme fellowship for funding, North CaliforniaEarthquake Data Centre for seismic data and Calpine Ltd. for hydraulic data.
Hybrid MT:
Kwiatek, G., P. Martínez-Garzón, and M. Bohnhoff(2016). HybridMT: A MATLAB/Shell environment package for seismic moment tensor inversion and refinement, Seismol. Res. Lett.
NonDC results:Martínez-Garzón, P., G. Kwiatek, M. Bohnhoff, and G. Dresen (2017). Volumetric components in the earthquake source related to fluid injection and stress state,Geophys. Res. Lett., 44
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Other slides
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2nd Schatzalp Workshop on Induced Seismicity, 2017
NDC in natural and induced seismicity
Natural degassing of CO2, volcanic environments
3/14
Geothermal stimulation, hydraulic fracturing
e.g. Miller et al, 1998; Dreger et al., 2000;Vavrycuk, 2002;
e.g. Cuenot et al., 2006; Fischer and Guest, 2011; Boyd et al., 2015
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Distribution of - NDC components
12/15
- ISO and CLVD tend to decrease during high injections
- ISO and CLVD tend to cluster around the open-holes
A Thermal shrinking?
B Other processes …?
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Hybrid-MT Moment tensor calculation
6/16
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2nd Schatzalp Workshop on Induced Seismicity, 2017
HybridMT moment tensor calculation
5/14
Gij=Gi
Gij=Gi
Iterative refinement of MTs by removing path effects and correcting for wrong sensor gain
Kwiatek et al., 2016
![Page 19: Geothermal induced seismicity: What links source mechanics ... · Geothermal induced seismicity: What links source mechanics and ... Analysis of large number of MTs to investigate](https://reader031.vdocuments.site/reader031/viewer/2022022510/5adb6bd97f8b9a4a268b481e/html5/thumbnails/19.jpg)
2nd Schatzalp Workshop on Induced Seismicity, 2017
Stress field change during peak injections
Cycle 1 Cycle 2
Martínez-Garzón et al. ,GRL, 2013
• Corelation between flow rates and changes inthe stress field orientation.
• Significant changes (~ 20°) during peak injections
5/16
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2nd Schatzalp Workshop on Induced Seismicity, 2017
Azimuthal distribution of seismicity
Cycle-1Before peak injection During peak injection After peak injection
• Hypocentral distance increase during peak injections
• Fracture network aligned with SHMax
SHMax
8/16