Periodic Reporting for period 4 - BEFINE (mechanical BEhavior of Fluid-INduced Earthquakes)
Periodo di rendicontazione: 2022-09-01 al 2023-12-31
Fluids play a crucial role in fault zones and earthquake generation by reducing normal effective stress, thus lowering fault frictional strength and potentially triggering ruptures. Fluid injection-induced earthquakes (FIE) provide direct evidence of this effect, often associated with high fluid pressures at seismogenic depths. Despite its theoretical simplicity, understanding the mechanisms governing FIEs remained limited, hindering our ability to assess seismic hazards. This project aimed to advance our understanding of FIE mechanisms through multidisciplinary approaches, including:
- Installation of a new rock friction apparatus dedicated to FIE study.
- Low, intermediate, and high strain rate friction experiments to explore fluid influences on fault creep, stability, and weakening during earthquake propagation.
- Post-mortem fault analyses using advanced microstructural techniques.
- Calibration of theoretical friction laws with experimental and observational data.
These efforts led to fundamental discoveries in natural earthquake processes and induced seismicity management, addressing key challenges in geo-engineering and sustainable resource exploitation at the European scale, with significant economic and societal implications.
- Installation of a new rock friction apparatus dedicated to FIE study.
- Low, intermediate, and high strain rate friction experiments to explore fluid influences on fault creep, stability, and weakening during earthquake propagation.
- Post-mortem fault analyses using advanced microstructural techniques.
- Calibration of theoretical friction laws with experimental and observational data.
These efforts led to fundamental discoveries in natural earthquake processes and induced seismicity management, addressing key challenges in geo-engineering and sustainable resource exploitation at the European scale, with significant economic and societal implications.
Throughout our project, we made significant progress in understanding fluid-induced earthquakes and their interactions within geological formations, resulting in the publication of 32 peer-reviewed papers that contributed valuable insights to the scientific community.
In this endeavor, we developed a fluid-induced simulator ("FIRST) capable of reaching pressures up to 200 MPa and temperatures of 200°C. This simulator, equipped with 16 acoustic emission sensors, electrical conductivity measurement capabilities, and up to 16 strain gauges, allowed for comprehensive monitoring of seismic activity (Noel et al., 2021). Additionally, we constructed a 3-meter-long biaxial apparatus housing analog samples (Paglialunga et al., 2021). Upgrades to a High-pressure (400 MPa) and high-temperature (1000°C) gas medium triaxial apparatus (TARGET) and a High-speed biaxial friction machine (HighSTEPS) (slip up to 50 cm/s) enabled us to replicate fluid-induced earthquakes across the entire seismic cycle (Violay et al., 2021; Meyer et al., 2022).
In Work Package 1, we developed mechanism-based constitutive models describing faults’ frictional behavior and porosity permeability development during inter-seismic periods. Conducting high-temperature and high-pressure experiments over extended periods, we measured the seismic and transport properties of rock. Utilizing the high-temperature - high-pressure creep apparatus ‘TARGET’ and the newly developed “FIRST” apparatus, we measured:
1. The porosity and permeability of faults and surrounding matrix (Orellana et al., Sci rep 2022; Acosta, Maye, and Violay, JGR, 2020; Meyer and Violay Gji 2023).
2. The seismic velocities to measure the crack density and aspect ratio evolution during the earthquake cycle (Acosta and Violay RMRE, 2020; Paglialunga et al., GRL., 2021).
3. We developed a new setup for electrical conductivity to monitor time-dependent changes in pore fluid chemistry and real-time fluid-rock interactions (Lazari and Violay, in prep, Giorgetti and Violay in prep).
In Work Package 2, we clarified the role of pore fluids on fault stability and earthquake nucleation. Using ‘FIRST,’ we reproduced miniature-scale injection experiments and measured induced acoustic emissions and their characteristics. Tests with different injection rates, volumes, and fluid physical properties were performed (Cornelio and Violay, GRL 2020; Acosta et al., GRL, 2019). Independently measuring frictional rate parameters while controlling machine stiffness, pore pressure, and normal and shear stresses under brittle and semi-brittle conditions (Noel et al., 2019a, b; Noël, Passelègue, and Violay, JGR, 2021), we observed and modeled the spontaneous nucleation precursors and evolution of frictional parameters.
In Work Package 3, we experimentally tracked lubrication processes during co-seismic sliding, reproducing co-seismic slip in a laboratory. We obtained unprecedented datasets on frictional dynamic weakening to understand the energy budget of fluid-induced earthquakes (Paglialunga et al., EPSL 2022, and EPSL 2024). Investigating the thermodynamic properties of fluid and fluid viscosity, along with pore fluid pressure, facilitated seismic source interpretation (Acosta et al., 2018, Nature comm; Cornelio et al., 2019 Nat comm, Cornelio et al., 2019, JGR, Cornelio GRL, 2020, Cornelio and Violay, GJI, 2020, Paglialunga et al., JGR, 2023).
Finally, we proposed an earthquake mitigation strategy from deep geothermal reservoirs, based on stress preconditioning, as a proactive approach to managing seismic risks associated with geothermal energy extraction (Fryer et al., 2023).
In this endeavor, we developed a fluid-induced simulator ("FIRST) capable of reaching pressures up to 200 MPa and temperatures of 200°C. This simulator, equipped with 16 acoustic emission sensors, electrical conductivity measurement capabilities, and up to 16 strain gauges, allowed for comprehensive monitoring of seismic activity (Noel et al., 2021). Additionally, we constructed a 3-meter-long biaxial apparatus housing analog samples (Paglialunga et al., 2021). Upgrades to a High-pressure (400 MPa) and high-temperature (1000°C) gas medium triaxial apparatus (TARGET) and a High-speed biaxial friction machine (HighSTEPS) (slip up to 50 cm/s) enabled us to replicate fluid-induced earthquakes across the entire seismic cycle (Violay et al., 2021; Meyer et al., 2022).
In Work Package 1, we developed mechanism-based constitutive models describing faults’ frictional behavior and porosity permeability development during inter-seismic periods. Conducting high-temperature and high-pressure experiments over extended periods, we measured the seismic and transport properties of rock. Utilizing the high-temperature - high-pressure creep apparatus ‘TARGET’ and the newly developed “FIRST” apparatus, we measured:
1. The porosity and permeability of faults and surrounding matrix (Orellana et al., Sci rep 2022; Acosta, Maye, and Violay, JGR, 2020; Meyer and Violay Gji 2023).
2. The seismic velocities to measure the crack density and aspect ratio evolution during the earthquake cycle (Acosta and Violay RMRE, 2020; Paglialunga et al., GRL., 2021).
3. We developed a new setup for electrical conductivity to monitor time-dependent changes in pore fluid chemistry and real-time fluid-rock interactions (Lazari and Violay, in prep, Giorgetti and Violay in prep).
In Work Package 2, we clarified the role of pore fluids on fault stability and earthquake nucleation. Using ‘FIRST,’ we reproduced miniature-scale injection experiments and measured induced acoustic emissions and their characteristics. Tests with different injection rates, volumes, and fluid physical properties were performed (Cornelio and Violay, GRL 2020; Acosta et al., GRL, 2019). Independently measuring frictional rate parameters while controlling machine stiffness, pore pressure, and normal and shear stresses under brittle and semi-brittle conditions (Noel et al., 2019a, b; Noël, Passelègue, and Violay, JGR, 2021), we observed and modeled the spontaneous nucleation precursors and evolution of frictional parameters.
In Work Package 3, we experimentally tracked lubrication processes during co-seismic sliding, reproducing co-seismic slip in a laboratory. We obtained unprecedented datasets on frictional dynamic weakening to understand the energy budget of fluid-induced earthquakes (Paglialunga et al., EPSL 2022, and EPSL 2024). Investigating the thermodynamic properties of fluid and fluid viscosity, along with pore fluid pressure, facilitated seismic source interpretation (Acosta et al., 2018, Nature comm; Cornelio et al., 2019 Nat comm, Cornelio et al., 2019, JGR, Cornelio GRL, 2020, Cornelio and Violay, GJI, 2020, Paglialunga et al., JGR, 2023).
Finally, we proposed an earthquake mitigation strategy from deep geothermal reservoirs, based on stress preconditioning, as a proactive approach to managing seismic risks associated with geothermal energy extraction (Fryer et al., 2023).
Development of 'FIRST' Friction Apparatus: We spearheaded the development of a groundbreaking tri-axial friction apparatus named ‘FIRST’ (Fluid-Induced eaRthquake SimulaTor). Tailored exclusively for understanding fluid-induced earthquakes, FIRST operates within stress, pressure and temperature ranges typical of seismogenic crust and deep reservoirs.
Construction of a 3m Long Biaxial Shear Apparatus: In addition to FIRST, we engineered a 3-meter-long biaxial shear apparatus to comprehensively investigate dynamic rupture propagation.
Pioneering Experiments with Viscous Fluids: Our groundbreaking experiments involved injecting natural rocks with fluids of varying viscosities. These experiments demonstrated the effectiveness of elasto-hydrodynamic lubrication as a fault weakening mechanism, independent of rock lithology. We revealed that highly viscous fluids notably reduce fault resistance, with slip rates for elasto-hydrodynamic lubrication being significantly lower than those required for other weakening mechanisms. Additionally, we discovered that the presence of viscous fluids alters the energy dissipation during rupture processes and affects nucleation and propagation dynamics (Cornelio et al., 2019, 2020 a, b, c).
Microphysical Investigations of Fault/Fluid Interactions: Through meticulous experimentation under realistic stress, we explored the microphysics of fault/fluid interactions during dynamic earthquake propagation. Our findings highlight the critical role of thermodynamic couplings between rocks and fluids in controlling frictional heating, fault weakening, slip, and stress drop during laboratory earthquakes (Acosta et al., 2018).
Advancements in Scaling Relationships and Rupture Dynamics: We revisited scaling relationships for fault slip and successfully reproduced the complete spectrum of rupture velocities observed in nature in the presence of fluids. Supported by theoretical predictions derived from Linear Elastic Fracture Mechanics, we elucidated how initial stress levels (i.e. pore fluid) predominantly govern seismicity along faults (Passelègue et al., 2020).
Analysis of Dynamic Rupture on Analogue Samples: Dynamic rupture experiments on analogue samples revealed two distinct weakening processes: a sudden, abrupt weakening corresponding to LEFM fracture energy and a prolonged weakening controlled by friction processes such as thermal pressurization and flash heating of asperities. We demonstrated that the latter process, and consequently breakdown work, are scale-dependent (Paglialunga et al., 2022, 2024).
Construction of a 3m Long Biaxial Shear Apparatus: In addition to FIRST, we engineered a 3-meter-long biaxial shear apparatus to comprehensively investigate dynamic rupture propagation.
Pioneering Experiments with Viscous Fluids: Our groundbreaking experiments involved injecting natural rocks with fluids of varying viscosities. These experiments demonstrated the effectiveness of elasto-hydrodynamic lubrication as a fault weakening mechanism, independent of rock lithology. We revealed that highly viscous fluids notably reduce fault resistance, with slip rates for elasto-hydrodynamic lubrication being significantly lower than those required for other weakening mechanisms. Additionally, we discovered that the presence of viscous fluids alters the energy dissipation during rupture processes and affects nucleation and propagation dynamics (Cornelio et al., 2019, 2020 a, b, c).
Microphysical Investigations of Fault/Fluid Interactions: Through meticulous experimentation under realistic stress, we explored the microphysics of fault/fluid interactions during dynamic earthquake propagation. Our findings highlight the critical role of thermodynamic couplings between rocks and fluids in controlling frictional heating, fault weakening, slip, and stress drop during laboratory earthquakes (Acosta et al., 2018).
Advancements in Scaling Relationships and Rupture Dynamics: We revisited scaling relationships for fault slip and successfully reproduced the complete spectrum of rupture velocities observed in nature in the presence of fluids. Supported by theoretical predictions derived from Linear Elastic Fracture Mechanics, we elucidated how initial stress levels (i.e. pore fluid) predominantly govern seismicity along faults (Passelègue et al., 2020).
Analysis of Dynamic Rupture on Analogue Samples: Dynamic rupture experiments on analogue samples revealed two distinct weakening processes: a sudden, abrupt weakening corresponding to LEFM fracture energy and a prolonged weakening controlled by friction processes such as thermal pressurization and flash heating of asperities. We demonstrated that the latter process, and consequently breakdown work, are scale-dependent (Paglialunga et al., 2022, 2024).