In this session, we invite contributions from research aimed at investigating the interaction of the above processes during exploitation of underground resources, including hydrocarbon extraction, wastewater disposal, geothermal energy exploitation, hydraulic fracturing, gas storage and production, mining, and reservoir impoundment for hydro-energy. We particularly encourage novel contributions based on laboratory and underground near-fault experiments, numerical modelling, the spatiotemporal relationship between seismic properties, injection/ withdrawal parameters, and/or geology, and fieldwork. Contributions covering both theoretical and experimental aspects of induced and triggered seismicity at multiple spatial and temporal scales are welcome.
Orals: Wed, 6 May, 14:00–18:00 | Room D3
The global energy transition increasingly relies on the sustainable use of the subsurface, which commonly involves fluid injection. Such injection can induce earthquakes, posing significant challenges to the safety and operability of geo-energy applications. Addressing these challenges requires a geomechanical understanding of induced seismicity and the coupled subsurface processes that govern it. This Award Lecture introduces recent research on fluid injection-induced earthquakes, spanning the evaluation of causal mechanisms to an in-depth understanding of the fault-slip processes that control earthquake magnitude and frequency.
The first part of the presentation focuses on identifying and evaluating the causal mechanisms for injection-induced earthquakes. The problem is formulated as assessing the susceptibility of fracture and fault slip driven by coupled thermo-hydro-mechanical (THM) processes in fractured porous media. Through several geo-energy case studies, it is demonstrated that induced seismicity commonly results from fracture and fault reactivation through multiple, co-occurring mechanisms. The relative contribution of these mechanisms largely depends on regional geology, fracture and fault properties, ambient stress conditions, and operational parameters. Fluid overpressure typically develops rapidly following injection and may influence a large area, depending on hydraulic connectivity and fault permeability. Poroelastic stressing accompanies fluid pressurisation, with its contributions controlled by the distance to susceptible faults and fault orientation relative to the ambient stress field. Thermal stressing is generally more spatially localised around injection wells but can become dominant over longer timescales. In addition, fault slip-induced stress transfer can explain seismicity beyond the region affected by fluid pressure and poroelastic stress changes. Understanding these mechanisms enables the development of physics-based approaches for induced seismicity hazard assessment that explicitly account for both geological conditions and operational strategies.
The second part of the presentation addresses fault frictional slip processes that ultimately control the earthquake magnitude and frequency. Three key governing processes are identified for injection-induced fault slip: fluid pressurisation, hydraulic diffusion, and frictional nucleation, each characterised by a distinct timescale. Their interactions give rise to a wide range of induced earthquake behaviours. To disentangle their combined effects, a coupled hydro-mechanical-frictional modelling framework was developed that integrates frictional contact models for faults with poroelastic models for surrounding rocks. The results have shown that frictional properties exert first-order control on fault slip regimes and the maximum earthquake magnitude, whilst fluid pressurisation primarily governs earthquake frequency and also influences the maximum magnitude through poroelastic stressing. These effects are further modulated by hydraulic diffusion, highlighting the role of reservoir hydraulic conductivity in controlling how injected fluids interact with distant faults. Building upon this understanding, this contribution illustrates how fluid pressurisation rate influences induced earthquake magnitude and frequency, and discusses the implications for designing injection strategies that minimise seismic risk while maintaining operational efficiency.
Acknowledgement: I gratefully acknowledge the support and nomination by Prof. Sevket Durucan, Dr. Suzanne Hangx, Prof. Chris Spiers, Prof. Paul Glover, and Prof. Keita Yoshioka, and the many collaborators who contributed to the research presented.
How to cite: Cao, W.: Understanding fluid injection-induced earthquakes: From causal mechanisms to fault frictional slip, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13423, https://doi.org/10.5194/egusphere-egu26-13423, 2026.
The injection of produced water back into producing permeable formations is regarded to be of low risk of inducing earthquakes because injection into producing conventional reservoirs generally does not lead to a net increase in reservoir pressure. The rise of production from tight unconventional reservoirs, on the other hand, required injection into non-producing aquifers. While unsurprising in hindsight, the concomitant increase in induced seismicity was unexpected based on the assumption, later shown to be false, that faults in stable cratonic sedimentary basins such as those in Texas and Oklahoma are not critically stressed. Complicating matters more, seismicity preferentially occurred in crystalline basement well below the injection target. Geomechanical models demonstrate that this response can be attributed to poroelastic stresses that are active over a larger distance and greater depth than the direct pore pressure disturbance. Our fully coupled poroelastic finite element simulations also demonstrated that in basins of large-volume injection, stress changes cannot be attributed to a single well or injection operation but reflect the cumulative effect of multiple disposal and production wells on a regional scale, making mitigation significantly more challenging. The difficulty of hindcasting observed seismic events on known and well-instrumented faults also demonstrated that effective forecasting of a seismic response would be difficult. This presentation will discuss viable approaches to mitigating the induced seismicity risk, concluding that active pressure management and avoiding injection in close vicinity to known large faults or close to infrastructure are perhaps the most effective approaches for mitigating earthquake risk associated with large-volume injection of wastewater and CO2 into aquifers.
How to cite: Eichhubl, P., Haddad, M., and Bump, A.: The geomechanics of induced seismicity associated with large-volume fluid injection—implications for risk mitigation , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15038, https://doi.org/10.5194/egusphere-egu26-15038, 2026.
To assess seismic hazard in the Groningen gas field, it is crucial to understand earthquake source processes, including the locations of nucleation and possible arrest. These fundamental characteristics, however, remain poorly constrained by seismological observations due to limited resolution. Interpretations of seismological observations are often inconsistent because the focal depth inversion uncertainty (~300 m) is comparable to reservoir thickness (50-300 m). Two fault segments, the velocity-weakening anhydrite layer within the caprock sequence and the velocity-strengthening sandstone reservoir experiencing substantial healing, are suggested to be seismogenic [1]. However, their respective roles in nucleation and rupture remain unclear. Additionally, whether ruptures can propagate into the over- and underburden layers is also debated, yet this is a key constraint for the maximum possible earthquake magnitude (Mmax).
Here, we use physics-based earthquake sequence simulations to investigate how stratigraphic layering, lithology-dependent elastic and frictional properties, and long-term fault healing govern rupture behavior. We find that earthquake nucleation consistently occurs within the sandstone reservoir, even when velocity-weakening friction is assigned to the overlying anhydrite caprock. Rupture propagation is predominantly confined to the reservoir thickness, with only limited penetration into adjacent formations. The anhydrite can only be activated, in rare cases, through rupture propagation. Introducing mechanical heterogeneity exerts a dominant control on rupture behavior by substantially suppressing slip rates and limiting rupture extent, whereas frictional heterogeneity has a comparatively minor effect in the opposite sense. Fully runaway rupture into the underburden is exceedingly rare. It only occurs in one out of 2,000 simulations and requires an extreme and unlikely combination of geometric, mechanical, and frictional conditions. Statistical mapping of simulation outcomes onto the Groningen fault network indicates that most fault segments have 5% or less likelihood of rupture propagating over a distance larger than the reservoir thickness. The likelihood of fully runaway rupture is 0.3%–1% only in a few peripheral regions beyond the locus of recorded earthquake occurrence and below 0.3% elsewhere. Together, these results demonstrate that lithological heterogeneity imposes strong physical constraints on rupture extent, providing robust, physics-based limits on Mmax and improving seismic hazard assessment for Groningen and other energy-producing regions.
[1] Li, M., Niemeijer, A., Van Dinther, Y. (2025, Nat. Comm.) https://doi.org/10.1038/s41467-025-63482-3.
How to cite: Li, M., Niemeijer, A. R., Vossepoel, F. C., and van Dinther, Y.: Nucleation and rupture of induced earthquakes in Groningen confined to the gas reservoir, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8208, https://doi.org/10.5194/egusphere-egu26-8208, 2026.
Enhanced Geothermal Systems (EGS) aim to provide sustainable energy by increasing the permeability of deep, low-productivity reservoirs through hydraulic stimulation. While micro-seismicity is an expected outcome of stimulation, larger induced earthquakes such as those recorded in Basel (2006) and Pohang (2017) remain a major challenge for the safe deployment of deep geothermal projects. This highlights the need for physics-based models capable of resolving the coupled processes and fault behavior that control induced seismicity, and of assessing how reservoir properties and stimulation strategies influence seismicity rates and maximum magnitudes.
We present a numerical framework designed to investigate how coupled thermo-hydro-mechanical (THM) processes govern fault reactivation and induced seismicity in EGS. The model explicitly couples fluid flow, heat transfer, and stress evolution, and incorporates stress-dependent deformation, fault reactivation, and a built-in earthquake detection algorithm based on deviatoric strain rate. This approach enables consistent identification of induced events within simulations and quantification of their magnitudes, providing a process-based framework to explore the spatio-temporal evolution of seismicity. To resolve fault complexity and process coupling at high spatial and temporal resolution, the model is implemented using high-performance computing tools, enabling efficient exploration of a wide range of scenarios.
Preliminary simulations of the 2006 Basel project reproduce key seismic characteristics, including b-values and maximum magnitudes consistent with observations. Early tests on different fracture networks indicate that fracture size strongly influences the resulting seismicity. Ongoing work systematically investigates the roles of fracture size, fracture criticality, and stress ratio in controlling induced seismic behavior. Overall, this modelling framework provides a flexible tool to explore the physical mechanisms driving induced seismicity in EGS and to support the development of safer stimulation strategies.
How to cite: Toussaint, G., Miller, S. A., and Valley, B.: Investigating fracture and stress controls on induced seismicity in geothermal reservoirs with a coupled THM model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11254, https://doi.org/10.5194/egusphere-egu26-11254, 2026.
Identifying and distinguishing induced seismicity from background regional tectonic activity remains a major challenge within tectonically active settings, due to the overlap between natural seismicity and seismicity potentially triggered by human activities. Induced seismicity refers to earthquakes generated or modulated by anthropogenic processes such as reservoir impoundment, fluid injection or extraction, and mining. While mining-induced seismicity has been shown to increase seismicity rates and magnitudes in tectonically stable regions, fundamental uncertainties remain regarding the spatial extent of mining influence and its detectability in areas with high background tectonic activity. The case of study is in the Central Andes (18-36°S), in the Chilean Andean Margin. Here, long-lived subduction has shaped well-defined metallogenic belts hosting major metallic ore deposits, within which Chile has developed a long history of open-pit and underground mining across diverse geological and operational settings. We use regional crustal seismicity from a recently published regional seismic catalog, together with a database of large-scale open-pit and underground mining operations in Chile, to systematically evaluate spatial and statistical relationships between seismicity patterns and mining activity. Specifically, we apply a three-phase framework to identify seismic events with a higher likelihood of mining-induced origin. We first define a 15 km depth threshold to separate shallow seismicity potentially influenced by mining from deeper regional tectonic events, and distinguish near-field from far-field seismicity based on proximity to mining operations. We then apply a nearest-neighbor clustering method to identify stochastically independent events, which are more likely to be induced. Finally, distance to mines and clustering information are combined into a linear weighted metric that quantifies the likelihood of induced seismicity. The results reveal a marked daily temporal anomaly in shallow seismic behavior (depth < 15 km), where an increase in activity is observed in the near field of mines between 16:00 and 22:00, aligning with the mines’ primary operational windows and blasting schedules. Within this time window, the probability of events belonging to a tectonic cluster decreases, thereby increasing the likelihood that they are induced seismicity rather than aftershock sequences. The primary finding highlights a daily six-hour window that concentrates 70% of the total seismic activity in the near field of mines. This represents a concentration 2.8 times higher than normal compared to regional seismicity, which lacks a preferred time frame. These observations indicate that mining activities can impose a measurable temporal signature on seismicity, even within a tectonically active subduction margin, contributing to the broader understanding of how anthropogenic processes interact with natural seismic systems.
How to cite: Ravest, B. and Roquer, T.: Spatial and Temporal Metrics for the Identification of Mining-Induced Seismicity: The Case of the Chilean Andean Margin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4084, https://doi.org/10.5194/egusphere-egu26-4084, 2026.
How to cite: Antunes, V., Simon, V., Toledo, T., and Kraft, T.: Network Performance Evaluation workflow and test for seismic monitoring of geothermal projects in Switzerland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21070, https://doi.org/10.5194/egusphere-egu26-21070, 2026.
Seismic monitoring in underground coal mining environments is influenced by various anthropogenic and natural noise sources. The background noise, predominantly of mechanical origin, shows strong spatial and temporal variability. Some highly impulsive sources share common characteristics with genuine seismic events. Routine blasting activities within the mine and from surrounding regions also contribute significantly to the recorded data. Mining-triggered sources such as microseismicity, subsidence, roof falls, and occasional sensing of tectonic earthquakes originating from distant locations further contribute to the recorded data. The combined influence of these sources strongly affects the performance of conventional processing workflows, frequently resulting in false detections and event misclassifications.
In this study, continuous seismic data recorded in an underground coal mine using eight short-period seismometers over a six-month duration are analysed to characterise signal and noise properties across temporal, spectral, and spatial domains. Spectral persistence, correlation metrics, and multichannel signal-processing techniques are used to identify dominant noise sources and assess their influence on the recorded waveforms. Persistent mechanical activity is shown to dominate the spectrum, with numerous harmonics and broadband noise, motivating the use of multiscale decomposition methods.
We evaluate the performance of Empirical Mode Decomposition (EMD) and Variational Mode Decomposition (VMD) for multiscale analysis. Our results show that EMD can introduce spurious low-frequency modes that are absent from the original signals and can therefore be misinterpreted. In contrast, VMD’s constrained-bandwidth formulation yields more physically meaningful scale separation. The multivariate extension of VMD (MVMD) has been used for better mode alignment and correlation across channels.
Overall, these results demonstrate the advantages of constrained, multivariate multiscale methods for the characterization of signal and noise with implications for improving seismic monitoring and event classification in complex environments.
How to cite: Prasada Raju, P. V. M. V. and Roy, P. N. S.: Multi-scale Characterization of Seismic Noise and Signals in an Underground Coal Mine, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7196, https://doi.org/10.5194/egusphere-egu26-7196, 2026.
Fluid injection in the subsurface for the purpose of CO2 sequestration, geothermal heat extraction or energy storage has frequently caused faults activation and seismicity, raised the communities’ concerns and ultimately resulted in project shutdown. In order to understand earthquakes, a set of unique experiments are being conducted in Bedretto Underground Laboratory for Geosciences and Geoenergy located at 1,000 m depth under the Swiss Alps. In these suites of experiments, small-scale non-damaging earthquakes are induced via water injection into a well-known and well-characterised fault.
A set of three borehole tiltmeters were deployed in the vicinity of the injection borehole and its data were used for analysing the fault’s behaviour during and after injection. A 3D finite element model (CSMP-HF) was utilised to predict the tilt vectors at specified stations from a set of prescribed input data (geometry, loading, stiffness, etc.), and a residual (cost) function was defined based on Bayesian framework to evaluate the closeness of the model predictions to the field measurements. Finally, a Differential Evolution optimisation technique was used to locate the global minima of the residual (cost) function, corresponding to the best set of input data. The inversion model results confirmed that both shear slip and opening (dilation) deformations occurred not only on the target fault, but also on another transverse fault. The inversion model was capable of accurately finding the location of “unknown” secondary fault which was consistent with log data gathered from another observation wellbore. The shear slippage consisted of both dip-slip (vertical) and strike-slip (horizontal) deformation, consistent with measured in-situ stresses.
How to cite: Salimzadeh, S., Lambiase, A., Gischig, V., Kasperczyk, D., Meier, M.-A., Hertrich, M., and Rinaldi, A.: Shear slip and opening of existing faults during fluid injection: insights from tilt measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6012, https://doi.org/10.5194/egusphere-egu26-6012, 2026.
The Utah Frontier Observatory for Research in Geothermal Energy (FORGE) is a field-scale laboratory for the study of enhanced geothermal systems (EGS) in low-permeable granitic and metamorphic basement rocks. Utah FORGE comprises a highly deviated injection–production well pair reaching a depth of ~2.5km and temperatures above 220°C. The site is monitored by multiple comprehensive microseismic networks with sensors installed at the surface, in shallow boreholes, and in deep boreholes at reservoir level. Following high-pressure hydraulic stimulation campaigns in 2022 and 2024, the wells were successfully connected through at least two principal fracture zones.
We study the induced microseismicity and its relation to flow path creation processes by performing waveform-based full moment tensor (MT) inversions for >180 events (local magnitude ML 0.0–1.9) recorded during the 2024 stimulations. Including non–double–couple (non-DC) or, more specifically, isotropic components helps characterize a complex reservoir development. Locally, most events exhibit highly similar strike-slip mechanisms consistent with the regional stress field, though minor rotations are observed between different fractured zones. We interpret well-resolved positive isotropic components as indicators for tensile opening components in the microseismic events. The maximum isotropic component increases with cumulative injected volume. Interestingly, the tensile components are more pronounced in areas dominated by fault reactivation compared to zones characterized by the opening of new hydraulic fractures and fracture networks. Our analysis highlights the complex interplay between the hydraulic activation of pre-existing fractures and the hydraulic opening of newly formed macrofractures during the stimulations at Utah FORGE. While resolving microseismic non-DC components requires a thorough, challenging analysis of resolution and uncertainties, their inclusion in routine monitoring can help illuminate not only where the reservoir is breaking but also how the hydraulic connection is established.
How to cite: Niemz, P., Petersen, G., Rutledge, J., Whidden, K., and Pankow, K.: Signatures of flow path creation in isotropic components of microseismic moment tensors at Utah FORGE, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14235, https://doi.org/10.5194/egusphere-egu26-14235, 2026.
Hydraulic-fracturing (HF) induced seismicity has attracted growing global attention, with the recorded maximum magnitudes reaching up to M6.0 in the southern Sichuan basin, China. How to mitigate the induced seismic hazard is key for safe energy development. Three mechanisms are proposed to explain earthquake triggering during HF: fluid diffusion, poroelastic stress perturbations, and aseismic slip, which can act individually or in combination. Although fluid diffusion is widely regarded as the primary driver, tracking pore-pressure evolution in near real time and quantifying its role in the nucleation of moderate-to-strong earthquakes remains challenging. Here we apply a non-tomographic Vp/Vs method (Lin and Shearer, 2007) to the southern Sichuan Basin, China and analyze the spatiotemporal variations of near-source Vp/Vs during three moderate M3-M4 HF induced earthquake sequences. Benefiting from abundant clustered induced seismicity and dense seismic arrays, we resolve Vp/Vs changes at a high resolution of ~2 days and ~150 m. We observe a consistent increase in Vp/Vs from ~1.73 to ~1.80 prior to the moderate-sized earthquakes, suggesting progressive pore-pressure buildup that culminates in seismic slip. In addition, the elevated pore pressure precedes eventual seismic slip by ~5–10 days, highlighting a preparatory phase for earthquake nucleation, which could be a valuable time window for making injection parameter adjustments to mitigate seismic hazard. The ability to resolve observable changes that precede moderate seismic events on such time scales suggests that the in-situ Vp/Vs approach offers a promising near-real-time monitoring strategy for seismic hazard assessment in a HF setting.
How to cite: Xu, J., Liu, Y., Li, J., Roth, M., Harrington, R., and He, Y.: Elevated in-situ Vp/Vs preceding M > 3 hydraulic-fracturing induced earthquakes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8567, https://doi.org/10.5194/egusphere-egu26-8567, 2026.
The Hverahlíð high-temperature geothermal field is located in the southern part of the Hengill volcanic complex in southwest Iceland. Prior to the onset of geothermal production in 2016, seismic activity in the area was limited. Since then, persistent micro-seismicity has been detected, characterised by a diffuse spatial pattern and only minor swarm activity. Despite covering just ~2 km², Hverahlíð hosts some of Iceland’s most productive geothermal wells, with measured temperature exceeding 300°C at around 1.5 km depth.
In this study, we analyse seismicity in Hverahlíð from 2016 to 2025, recorded by a varying number of seismometers (14 to 40) deployed across the wider Hengill area. The core network consists of permanent stations operated by Iceland GeoSurvey (ÍSOR) for ON Power, supplemented by the regional SIL-network of the Icelandic Meteorological Office. Additionally, 30 temporary stations were installed during the COSEISMIQ project (2018–2021), significantly improving the local detection capability and spatial resolution.
Seismicity in Hverahlíð is dominantly micro-seismicity, with ~90% of the activity of ML < 1.0, and a magnitude range of ML -0.3 to 3.5. High-resolution relative relocations show that seismicity is confined to 2-3.5 km depth below sea level, i.e., located slightly below the bottom of the production wells and organised in one main cluster and another significantly smaller cluster, both trending NNE-SSW within the production area.
Although the Hverahlíð area is highly fractured with cross-cutting faults trending from NNE-SSW to ENE-WSW, the observed seismicity does not directly illuminate known surface faults. Instead, the earthquake distribution reflects the geothermal production zone, closely matching the geometry of the geothermal system as inferred from existing resistivity models. The earthquake depth distribution may reflect, at least partially, cooling and thermal contraction of the hot host rock induced by deep fluid convection linked to the heat source of the geothermal system. Comparison with other high-temperature geothermal systems in Iceland suggests that the seismicity may delineate the base of a highly permeable convective geothermal reservoir.
Despite considerable production driven pressure draw-down in Hverahlíð, only around 18% of earthquake source mechanisms show pure normal faulting, whereas 55% show pure strike-slip faulting. As the production area will grow in lateral extent in coming years through planned step-out-wells, a corresponding increase in the lateral extent of seismicity is possible.
How to cite: Ágústsdóttir, T., Benediktsdóttir, Á., Gudnason, E. Á., Magnússon, R. L., Halldórsdóttir, S., Axelsson, G., Helgadóttir, H. M., and Gunnarsdóttir, S. H.: Micro-seismicity in the Hverahlíð high-temperature geothermal field, Hengill, SW-Iceland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14814, https://doi.org/10.5194/egusphere-egu26-14814, 2026.
Underground mining induces seismicity and surface displacement. In Poland, in the Legnica Glogow Copper District near Wroclaw, induced earthquakes are particularly frequent with earthquakes of Mw3 and larger occurring many times a year. These earthquakes have shallow hypocentres of often less than 1 km and mostly above the mined copper layer.
The area around the mines also experiences a fast continuous surface subsidence of several millimeters per year caused by rock as well as groundwater extraction. This surface motion is observed through geodetic measurements on the ground and from space. The rate of surface motion is spatially very heterogeneous. Across wide areas above the active mining it even exceeds 10 mm/yr. Also sudden coseismic acceleration of surface motion is observed at the time of the larger earthquakes through space-borne InSAR. In these cases we often observe motion of several centimeters within a few days and with spatial extensions reaching a few kilometers.
Despite safety measures, the occurrence of some, also larger earthquakes is unexpected in space and time, which poses a particular threat to workers in the mines and but also to the subsurface mine structures as well as generally to the people, settlements and infrastructure above ground.
Our study investigates a number of larger events of the recent years by analyzing the locally recorded seismic waveforms jointly with measurements of the surface displacements based on InSAR and partly GNSS measurements. We aim to precisely locate the source processes of larger induced earthquakes and to characterize them as an interplay between shear-failure and collapse using full moment tensor models in a fully Bayesian inference framework. Potentially we can relate collapse and failure to the mining activities or other influences and improve our understanding of these unwanted events for mitigation measures.
The observations are best explained by large negative isotropic components accompanied by apparently significant shear failure mechanisms. Another finding is that our moment estimates systematically exceed the local catalog values. Challenges to be discussed are the impact of our single short-duration source model for possibly an accumulation of multiple events, possibly involving a larger volume and a longer duration, and the potential bias introduced by a simplified velocity model.
How to cite: Sudhaus, H., Witkowski, W., and Moser, S.: Investigating the source processes of underground-mining induced earthquakes based on geodetic and seismic observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12114, https://doi.org/10.5194/egusphere-egu26-12114, 2026.
Seismic monitoring is a critical component of Carbon Capture and Storage (CCS) projects, ensuring the containment security of injected fluids and assessing the risks associated with induced seismicity. While fluid injection is known to alter effective stress and pore pressure—potentially inducing velocity changes or fault reactivation—distinguishing these deep subsurface signals from near-surface environmental variations remains a significant challenge. This study utilizes the passive source Horizontal-to-Vertical Spectral Ratio (HVSR) method to investigate the spatiotemporal variations of site response at the CO2 Containment and Monitoring Institute Field Research Station (CaMI.FRS) in Alberta, Canada, providing a robust baseline for long-term integrity monitoring. We analyzed continuous ambient noise data collected between September 2019 and October 2020 from a dense array of short-period seismic stations deployed around the injection well. The injection targets the Basal Belly River Formation at a depth of 300 m. Data processing involved dividing daily records into 150-second windows with 50% overlap, followed by bandpass filtering (0.2–20 Hz) and Konno-Ohmachi smoothing to calculate daily stability-weighted HVSR curves. The results reveal a consistent fundamental resonance frequency (f0) centered at approximately 2 Hz across the study area, corresponding to a soft sediment thickness of 100–150 m overlying the bedrock. While f0 remained relatively stable throughout the monitoring period, the H/V peak amplitude (amplification factor) exhibited significant seasonal time-varying characteristics. Specifically, a strong positive correlation was observed between the amplification factor and environmental variables, including atmospheric temperature, precipitation, and groundwater levels. The amplification factor reached its annual maximum (~2.5–2.6) during the warm, wet summer months (June–August) and dropped to its minimum (~1.5–1.8) during the frozen winter months. These findings suggest that variations in near-surface saturation and soil properties, driven by seasonal climate cycles, significantly modulate seismic site response. Consequently, for effective HVSR-based monitoring of deep CO2 plumes or leakage pathways, it is imperative to decouple these shallow environmental effects from the signals of deep geological alterations. This study demonstrates the efficacy of time-lapse HVSR as a low-cost, non-invasive tool for characterizing site response dynamics and highlights the necessity of multi-physics environmental calibration in CCS monitoring protocols.
How to cite: Li, T., Yu, T., Yu, N., Yang, Y., and Gu, Y. J.: Time-Lapse HVSR Analysis for Shallow Subsurface Monitoring at the CaMI.FRS CO2 Sequestration Site , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12093, https://doi.org/10.5194/egusphere-egu26-12093, 2026.
A large hydropower complex is planned on the Lower Yarlung Tsangpo (YT) with an expected output roughly three times that of the Three Gorges Project. The planned hydropower complex lies in the eastern Himalayan syntaxis, which is characteristic of intricate fault systems, high tectonic strain rates, and strong topographic variations. Reservoir impoundment in such a geologic setting may lead to unintended consequences such as induced seismicity and landslides. A pre-impoundment risk assessment is imperative for the region and the project. With regional faults and stress information, we perform an analysis to identify the fault segments that may be affected by reservoir impoundment and lead to seismicity.
The existing observations from hydraulic fracturing tests indicate that the rotation of SHmax orientation shows similarities with the changes in the YT course. To obtain abundant and diverse stress information, we compiled 145 focal mechanisms for the study area covering the period of 2000 - 2023. Moment magnitudes concentrate around 1.5 - 4, and hypocenter depths are in the upper crust (≤ 15 km). Given the complexity of the fault system and the pronounced heterogeneity in the number and distribution of focal mechanisms, we partitioned the study area into four subregions and performed focal mechanism stress inversions separately for each subregion. The inversion results reveal a strike-slip regime in three subregions and a thrust faulting regime in one subregion. The stress ratios for all subregions lie in the range 0.6 - 0.8. The inverted SHmax orientations differ markedly between subregions, with a maximum discrepancy of ~58.5°.
To quantify fault destabilization risk, we employ a parameter termed ‘fault instability’ (FI). The FI range is from 0 to 1, ‘0’ for the most stable fault, while ‘1’ for the most unstable fault. It is quantified by fault frictional coefficient μf, fault strike and dip, stress field, and pore pressure. To consider the uncertainty in these input parameters, the Monte Carlo sampling is used to constrain the FI. Different fault segments exhibit markedly different FI values. Seismicity over the 23-year period predominantly occur on faults with high FI values, corroborating the qualification of the FI. FI distribution can inform dam siting and tunnel routing. We plan to build a 3D hydro-mechanical model that couples observed and inverted geological data, simulate pore pressure diffusion and water loading effects on Coulomb stress, and assess the resulting changes in FI and induced seismicity risk.
How to cite: Wang, H., Ge, S., and Ma, X.: Assessing induced seismicity risk for the Lower Yarlung Tsangpo hydropower complex, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1912, https://doi.org/10.5194/egusphere-egu26-1912, 2026.
Induced seismicity associated with gas production in the Groningen gas field, north-eastern Netherlands, underscores the need for improved forecasting of reservoir compaction and stress redistribution during long-term subsurface exploitation. While current geomechanical models typically assume laterally homogeneous reservoir properties, growing evidence suggests that sedimentary heterogeneity exerts a first-order control on sandstone compactional behaviour. This contribution integrates field-scale petrographic analysis with laboratory geomechanical experiments to quantify how inherited geological heterogeneity governs the mechanical response of the Permian Rotliegend reservoir.
A quantitative petrographic dataset of more than 300 samples from fifteen wells demonstrates that porosity loss across the field is overwhelmingly dominated by mechanical compaction associated with rapid Late Permian burial beneath the Zechstein evaporites, accounting for 55–95% of total porosity reduction. However, compaction efficiency varies systematically with depositional texture and early cementation rather than burial depth alone. Grain size, sorting, lamination, and early dolomite and anhydrite cementation controlled initial packing density and grain-contact geometry, leading to strong spatial heterogeneity in preserved intergranular volume and inferred mechanical properties.
To directly test the mechanical implications of this heterogeneity, we conducted triaxial deformation experiments on Rotliegend sandstones with comparable porosity (~12%) but contrasting cementation styles and clay contents. Experiments performed under reservoir-relevant stress and temperature conditions show that approximately 30% of total strain is inelastic, with time-dependent deformation occurring during stress relaxation phases. Samples containing higher clay contents accumulated the largest inelastic strain, while strongly dolomite- and quartz–anhydrite-cemented sandstones exhibited higher stiffness but still significant non-elastic deformation. Microstructural analyses using SEM reveal grain-scale damage patterns consistent with cement- and clay-controlled deformation mechanisms.
Together, these results demonstrate that reservoir compaction in Groningen is strongly conditioned by inherited sedimentary and diagenetic heterogeneity that is not captured in conventional homogeneous models. Incorporating these controls into geomechanical frameworks is essential for more realistic prediction of reservoir deformation and associated induced seismic hazard during subsurface resource exploitation.
How to cite: Miocic, J., Mulder, S., and Bublik, D.: Sedimentary heterogeneity and rock mechanical controls on reservoir compaction in the Groningen gas field, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11445, https://doi.org/10.5194/egusphere-egu26-11445, 2026.
During the siting of hydraulic-fracturing (HF) wells within industrial activity areas, identifying potential seismogenic faults and effectively avoiding them is critical for mitigating induced seismicity risk. Meanwhile, characterizing the fine-scale structures of seismogenic faults provides the essential foundation for analyses of the mechanisms and rupture processes of induced earthquakes. However, multiple case studies have demonstrated that, even where seismic reflection data are available, it remains difficult to identify small-displacement seismogenic faults, particularly those dominated by strike-slip faults. Consistently, the four representative M5+ induced earthquakes in the Changning and Weiyuan shale gas blocks of the Sichuan Basin also exhibit difficulties in identifying the seismogenic faults from seismic reflection data. Moreover, the scales of faults that can be identified through seismic reflection data and related interpretation methods, and their corresponding seismogenic potential, remain to be systematically defined and quantitatively constrained. This study integrates spatiotemporal data from HF operations, seismicity data, and high-resolution 3D seismic reflection data, together with surface deformation measurements, to address the above questions.
The results show that potential seismogenic faults with moment magnitude (Mw) greater than approximately 3.3 that displace strong reflection horizons can be effectively identified using high-resolution 3D seismic reflection data. In addition, the associated structures of small-displacement strike-slip faults facilitate their recognition in seismic reflection profiles. A common feature of the seismogenic fault systems of the four representative earthquakes is that small-displacement subsidiary faults (including strike-slip faults) intersect the fracturing wells within the reservoir interval, forming downward migration pathways for fracturing fluids and thereby activating the underlying thrust or strike-slip seismogenic faults. More importantly, such small-displacement faults are widely developed within the fractured intervals of the Sichuan Basin shale gas fields, yet their identification remains challenging. As a result, numerous horizontal wells intersect these faults, constituting a key reason for the frequent occurrence of induced seismicity in these areas. The most effective approach to recognizing these faults is to trace multiple strong reflection horizons to construct structural maps. By applying multi-azimuth illumination and vertical stretching, fault traces can be visualized more clearly, in combination with various types of seismic reflection attribute volumes.
Beyond the Sichuan Basin, injection-induced earthquakes in most shale gas fields worldwide are also closely associated with small-displacement faults, particularly strike-slip faults. The failure to avoid such faults during the siting of HF wells is also likely a major reason for the frequent occurrence of induced seismicity in these areas. The small-displacement fault identification techniques presented in this study facilitate a more precise delineation of seismogenic fault system structure. More importantly, during well site selection, from the perspective of fault identification and avoidance based on 3D seismic reflection data, this study provides theoretical support and practical strategies for preventing induced earthquakes with a magnitude (Mw) greater than approximately 3.3. These findings also offer significant implications for the prevention of induced seismicity caused by fluid/gas injection in a broader range of applications.
How to cite: Ye, Y. and Lu, R.: Identification and Impacts of Small-Displacement Faults in Industry-induced earthquake: Insights from the Southern Sichuan Shale Gas Field, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2497, https://doi.org/10.5194/egusphere-egu26-2497, 2026.
Hydraulic fracturing operations in the Southern Sichuan Basin have generated significant induced seismicity, raising important questions about the underlying rupture processes. We analyze stress drops of 3,369 induced earthquakes (ML > 0.5) using a non-parametric generalized inversion technique with rigorous reference-station corrections. Our analysis reveals two key characteristics of these induced events: first, they exhibit systematically low stress drops (median 0.07 MPa) that show positive scaling with seismic moment, challenging classical self-similarity assumptions; second, we observe pronounced spatial variations in stress release that correlate with depth and fault structure. Notably, fluid diffusion drives rapid activation of fault asperities, resulting in repeated high-stress-drop ruptures (0.3-6.0 MPa) within short timescales of days. This accelerated rupture cycle differs fundamentally from tectonic earthquake recurrence patterns. Our findings demonstrate that induced earthquake rupture dynamics are controlled by the interplay of heterogeneous fault strength and rapid fluid pressurization, providing critical insights for developing targeted hazard assessment strategies in energy-producing regions.
How to cite: Chen, X., Tao, J., Liu, D., and Chen, H.: Stress Drop Variability and Rapid Fault Activation in Hydraulic-Fracturing-Induced Earthquakes: Insights from the Southern Sichuan Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2228, https://doi.org/10.5194/egusphere-egu26-2228, 2026.
Mining districts in Chile are located within one of the most seismically active tectonic environments on Earth, which makes it challenging to distinguish between natural crustal seismicity and seismicity potentially influenced by mining. A key open question is whether large-scale mining operations produce a measurable and spatially coherent statistical signature in the surrounding shallow crust. In this study, we evaluate this hypothesis using the Gutenberg–Richter b-value as a quantitative proxy for local stress conditions and the degree of rock mass damage and fracturing. We focus on the seismic environment surrounding major mining districts in Chile, restricting the analysis to shallow crustal events with depths shallower than 10 km. This depth filter aims to isolate the seismic response of the upper crust that is most likely to be affected by mining-related stress perturbations, while reducing the contribution of deeper subduction-driven tectonic seismicity. To resolve spatial variations at kilometer scale, we implement a high-resolution concentric-ring analysis centered on each mining district, using 1 km radial bins extending outward from the extraction centers. To ensure statistical robustness and comparability across sites, the magnitude of completeness (Mc) is estimated dynamically using the maximum curvature method, yielding reference values close to ML ≈ 1.87 for the analyzed catalog. The Gutenberg–Richter b-value is then computed using the Aki–Utsu maximum-likelihood estimator, providing a rigorous and stable framework for inter-site comparisons under contrasting geomechanical and operational settings. The analysis reveals clear and systematic differences depending on the mining method. Underground mining environments show a pronounced increase in b-value (b > 1.5) within the first ~5 km, consistent with elevated rates of microseismicity and enhanced brittle damage associated with caving-related processes. In contrast, open-pit operations exhibit a comparatively stable b-value pattern with lower spatial dispersion. In both settings, b-values progressively converge toward the regional tectonic reference level (b ≈ 1.0) with increasing distance from the extraction centers, suggesting a characteristic radius of direct mining influence on the order of ~15–20 km. These preliminary results show that kilometer-scale mapping of the Gutenberg–Richter b-value provides a sensitive and interpretable metric to quantify the spatial footprint of mining-related seismic perturbations in the shallow crust. The observed b-value gradients offer a practical tool for regional-scale geomechanical monitoring, supporting the discrimination between background tectonic seismicity and elastic stress changes induced by excavation and/or large-volume rock mass caving in Chilean mining districts.
How to cite: Roquer, T. and Ravest, B.: Mining-Related b-Value Anomalies in the Upper Crust: A High-Resolution Ring Analysis Across Chilean Mining Districts , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20770, https://doi.org/10.5194/egusphere-egu26-20770, 2026.
Hydraulic fracturing often induces complex seismic sequences that migrate across stratigraphically distinct formations. However, the mechanisms governing delayed triggering and vertical interaction through lithological boundaries remain poorly understood. In this study, we report a novel "coseismic valve" mechanism observed in the Weiyuan shale gas field, southern Sichuan Basin, where the multi-stage evolution of seismicity was strictly governed by pre-existing 3D mechanical stratigraphy.
Using a dense local monitoring array, we constructed a high-resolution catalog by the deep-learning-based LOC-FLOW workflow. This catalog revealed a vertically partitioned fault system, where the deep and shallow seismicity clusters are distinctly separated by a ~400 m thick low-velocity ductile barrier.This barrier mechanically isolated a deep, critically stressed segment (characterized by a low b-value) from a shallower, compliant damage zone. Our analysis reveals a paradox in the role of ductile layers: initially, the barrier acted as a "pressure seal," preventing fluid leak-off and facilitating high differential stress accumulation in the underlying reservoir. This confinement culminated in the nucleation of an Mw 3.6 mainshock with an anomalously high stress drop.
Crucially, finite fault inversion and isochrone back-projection demonstrate that the mainshock rupture propagated upward, dynamically breaching the ductile barrier. This mechanical breach effectively functioned as a valve, establishing a vertical conduit for hydraulic connectivity. Following a distinct 6-day delay, a diffusive seismic swarm erupted in the previously quiescent shallow segment, driven by the upward surge of overpressured fluids through the newly created fracture network.
Our findings challenge the conventional view of ductile layers merely as passive aseismic buffers. We demonstrate that they can play a dual role: serving as stress-concentrating seals that prime the system for nucleation, and as structural valves that, once ruptured, enable cascading seismic hazards. This dynamic interaction highlights the necessity of integrating 3D structural frameworks into seismic risk assessment for geo-energy projects.
How to cite: Tao, J., Chen, X., Liu, D., Chen, H., Zhao, Y., Niu, F., and Zhang, L.: The Dual Role of Ductile Barriers: From Stress-Concentrating Seals to Coseismic Valves in Induced Seismicity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2227, https://doi.org/10.5194/egusphere-egu26-2227, 2026.
Induced seismicity remains a major challenge for geothermal projects, with implications for public acceptance and operational risk management. Understanding how fluid injection interacts with fault structures to generate seismicity is therefore essential. The Húsmúli reinjection area in the Hengill geothermal field (SW Iceland) provides an ideal setting to investigate these processes due to its sustained induced seismicity and long operational history. Here, we present an improved seismicity catalog (2018–2021; COSEISMIQ project) and a waveform-based detection workflow that substantially increases catalog completeness and enhances spatiotemporal resolution.
We first improve the initial automatic catalog by re-picking events with unrealistic Vp/Vs ratios (Wadati analysis), high RMS location misfits, or unrealistic depths (e.g., airquakes). Phase picks are then refined using a cross-correlation (CC)-based repicking approach: events are clustered into waveform-similar families, traces are aligned and stacked to increase signal-to-noise, and consistent arrival times are obtained from a single-family reference pick. Missing picks are recovered by inspecting waveforms around the expected arrival time window and estimating phase onsets, accepting only traces with CC ≥ 0.65 with respect to other family members.
3D spatial clustering of the refined catalog reveals NE–SW oriented seismic lineaments consistent with mapped faults and inferred fluid migration pathways. In contrast, nearby E-W structures show little to no seismicity, suggesting permeability barriers and reservoir compartmentalization. Repeating earthquakes occur along narrow fault segments, indicating repeated rupture of localized slip patches. To further enhance detection, we use QuakeMatch, a single-station template matching workflow using high-SNR events as templates at the station with the best waveform quality and data completeness. This expands the catalog from 3,647 to 12,899 events, lowering the magnitude of completeness and revealing numerous low-magnitude earthquakes previously missed by the automatic STA/LTA processing due to low signal-to-noise or waveform overlap. The resulting catalog shows swarm-like activity typical of fluid-driven seismicity and episodic bursts. A prominent sequence on 15 November 2020 (MLX = 4.08) is preceded by foreshocks and followed by multiple MLX ≥ 3.0 aftershocks. Gutenberg–Richter analysis indicates a decrease in b-values prior to the mainshock, consistent with stress build-up and suggesting potential precursory behaviour relevant for operational monitoring.
How to cite: Kaur, S., Toledo, T., Kraft, T., and Simon, V.: Characterization of microseismicity at the Húsmúli reinjection area, Hengill Geothermal Field, Southwest Iceland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8098, https://doi.org/10.5194/egusphere-egu26-8098, 2026.
Induced seismicity remains a significant challenge for the development of deep geothermal energy projects, with continued challenges at both the scientific and operational levels.
Scientific level: Seismic monitoring at geothermal sites is commonly limited to periods of active operations such as hydraulic stimulation and testing, whereas datasets documenting the seismic response during shut-in and post-operational phases remain scarce. However, larger-magnitude earthquakes have been observed during shut-in phases, and in some cases months later, despite limited information on seismic activity during the active period. As a result, the processes governing delayed, larger-magnitude induced earthquakes remain poorly understood.
Operational level: During active operations, the spatio-temporal evolution of induced seismicity provides one of the few direct indicators of subsurface processes. Real-time insight into whether seismicity evolves as expected or migrates toward potentially hazardous structures is essential for timely mitigation. Advanced Traffic Light Systems (ATLS) assess seismic hazard and risk based on observed seismic responses and rely on statistical and hydromechanical models to forecast the likelihood of induced events over the following hours to days. The reliability of these forecasts critically depends on the quality of the underlying earthquake catalog. Improved detection and location of small events and more robust magnitude estimates can substantially enhance hazard assessments and operational decision-making.
To address these challenges, we introduce QuakeMatch (QM), a toolbox that leverages waveform similarity to improve seismic monitoring in both real-time and long-term applications. The workflow employs template matching based on events from a manually revised catalog, followed by refined magnitude estimation, event relocation of assembled events, and statistical analysis.
We demonstrate the application of QM using the case studies from the Basel and Haute-Sorne deep geothermal projects. The Basel case is currently covered by earthquake catalogs with strongly varying location precision and completeness. A template-matched catalog by Herrmann et al. (2019), covering the period 2006–2019, does not include relocations and has not been updated since its publication. Here, QM is used to build a homogeneous long-term catalog of consistently high-precision earthquake locations that will improve our ability to assess the long-term response of this field over two decades up to the present day. For the Haute-Sorne case, we demonstrate the real-time application of QM, illustrating its potential to better inform advanced induced-seismicity-mitigation procedures (e.g., ATLS) with more reliable, consistent, and sensitive earthquake catalogs. Together, these examples illustrate the potential of combining long-term catalog enhancement with real-time monitoring to support safer and more informed geothermal operations.
How to cite: Toledo, T., Simon, V., Kraft, T., and Diehl, T.: Enhancing Long-Term Seismic Analysis of Swiss Geothermal Projects through Waveform Similarity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13011, https://doi.org/10.5194/egusphere-egu26-13011, 2026.
Injection-induced seismicity in Enhanced Geothermal Systems (EGS) can migrate hundreds of meters from the well and often persists after shut-in, raising operational and hazard concerns. Here we present a cross-site comparative analysis of three stimulation campaigns—Soultz-sous-Forêts (France, 1993), Basel (Switzerland, 2006), and Utah FORGE Stage 3 (USA, 2022)—to identify the dominant controls on intermediate-field seismic migration.
Using a unified dynamic time-windowing framework, we track seismic front evolution via three complementary distance metrics and evaluate their relationships with injection rate, wellhead pressure, cumulative injected volume, hydraulic energy, seismicity rate, and modeled pore pressure at the migration front. Across all sites, cumulative variables—particularly injected volume, hydraulic energy, and injection duration—show the strongest and most consistent correlations with seismic front expansion, whereas instantaneous parameters exhibit weaker or site-specific influence.
Post-injection behaviors distinguish three migration regimes: (i) a pressure-limited regime at Soultz, where the front halts immediately after shut-in; (ii) a diffusion-dominated regime at Basel, with continued post-shut-in propagation; and (iii) a stress-sensitive, limited-diffusion regime at Utah FORGE, characterized by rapid early migration followed by stagnation. Building on these contrasts, we introduce a six-indicator radar classification that quantitatively distinguishes the three regimes.
Our results show that cumulative hydraulic forcing provides transferable, physically interpretable predictors of intermediate-field migration and that distinct post-shut-in signatures reflect underlying connectivity and stress conditions. This comparative framework supports improved seismic hazard assessment and operational planning for geothermal reservoir stimulation.
How to cite: Wang, Z., Pankow, K., Rinaldi, A., Verdon, J., and Main, I.: Cumulative Controls on Intermediate-Field Seismic Migration: Comparative Evidence from Three Geothermal Stimulation Campaigns, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1317, https://doi.org/10.5194/egusphere-egu26-1317, 2026.
Between April and June 2013, the GRT-1 well at the Rittershoffen geothermal site in the Upper Rhine Valley (France) underwent three distinct stimulation phases: first a thermal stimulation, then a chemical stimulation, and finally a hydraulic stimulation. These fluid injections significantly enhanced the injectivity index of the well, rendering it suitable for economic exploitation. Throughout these operations, a local surface seismic network continuously monitored the site, recording thousands of unfelt seismic events.
This study builds upon and refines the findings of Lengliné et al. (2017), who focused solely on the hydraulic stimulation of GRT-1, and Maurer et al. (2020), whose interpretations were constrained by uncertain absolute locations of seismic events, particularly in terms of depth. By employing an improved template matching technique and a relative location method, we established a comprehensive seismic event catalog comprising over 3,000 events.
This reliable catalog enables precise tracking of the reservoir’s seismogenic response to the successive yet distinct stimulation types, with high spatial and temporal resolution. Consequently, it allows for an investigation into the potential seismic interplay between these stimulations. Our analysis examines the evolution of key characteristics, including event distribution and clustering, b-value, and seismic injection efficiency across the stimulation phases. The observed differences prompt critical questions regarding the reliability of using responses from prior stimulations to forecast seismogenic behavior during subsequent operations, even for the same site.
How to cite: Gaucher, E., Lengliné, O., and Schmittbuhl, J.: Variability of the Seismic Response of the Rittershoffen Geothermal Reservoir to the Series of GRT-1 Stimulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9185, https://doi.org/10.5194/egusphere-egu26-9185, 2026.
Injection of fluids during reservoir stimulation aims to enhance reservoir permeability but induces seismic activity that persists for several hours to several months after injection has ceased. Physical and hybrid models have been successfully applied to reproduce and forecast observed seismicity rates during and after injection. However, these models are typically site-dependent, raising the question of whether a general relationship between pressure and seismicity decay can be observed across different sites and operations.
In this study, we investigate the correlation between post-injection pore pressure decay and the decrease in seismicity rate using data from multiple EGS injection operations that share similar properties. First, the performance of several empirical statistical models is evaluated to describe the decrease in seismicity rate. Second, wellhead pressure decay is shown to be best described by a simple exponential model. Lastly, we introduce a time-to-fraction metric to compare the pressure and seismicity evolution after shut-in. We show that the times required to reach a given fraction of the initial rate for both pressure and seismicity are correlated, with pressure evolution being slower than seismicity rate evolution. No correlation is observed between seismicity decay and injection parameters such as injected volume, average injection pressure, or injection duration. These observations suggest that pore pressure has a limited influence on seismicity decay, which has strong implications for reservoir management.
How to cite: Minetto, R., Wang, Z., Lengliné, O., and Schmittbuhl, J.: Investigating the Correlation Between Post-Injection Trailing Seismicity and Wellhead Pressure Decay in Enhanced Geothermal Systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14295, https://doi.org/10.5194/egusphere-egu26-14295, 2026.
Understanding how faults are activated and earthquakes are triggered is still a central challenge in seismology and seismic hazard assessment. Controlled hydraulic stimulation experiments offer a valuable opportunity to study these processes under well-constrained conditions and at spatial and temporal resolutions that are rarely achievable in natural settings. In this study, we present the results of three hydraulic stimulations experiments conducted at the Bedretto Underground Laboratory and monitored by a dense, high-sensitivity seismic network.
These experiments revealed a complex spatio-temporal evolution of induced seismicity, characterized by the activation of a multi-segment fault network. Two dominant seismic clusters were activated early on and show a clear spatial connection to the injection borehole, suggesting that pore pressure is the main driver of seismicity within these clusters. At later stages, a third cluster with a different orientation was activated, despite showing no obvious direct hydraulic connection to the injection interval. Seismicity within this cluster occurred with a temporal delay compared to the other two clusters. This suggests that the fault activation was likely driven by indirect processes such as aseismic deformation, stress transfer, and delayed fluid migration.
The observed fault network activation closely resembles patterns commonly reported in natural earthquake sequences. These findings suggest that the physical mechanisms controlling fault reactivation and earthquake triggering are largely independent of scale, linking controlled field experiments and natural earthquakes. Our results emphasize the importance of fault network geometry and stress interactions in understanding induced and natural seismicity.
How to cite: Rosskopf, M., Obermann, A., Rinaldi, A. P., Bröker, K., Villiger, L., and Giardini, D.: Fault Network Activation During Controlled Hydraulic Stimulation Experiments in the BedrettoLab, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12236, https://doi.org/10.5194/egusphere-egu26-12236, 2026.
A key challenge in induced seismicity is that fluid injection perturbs stress and pore pressure on faults with heterogeneous properties, leading to complex earthquake nucleation, migration and magnitude. The BedrettoLab (Bedretto Underground Laboratory for Geosciences and Geoenergies), located in the Swiss Alps, provides a unique natural testbed to study how these coupled hydro-mechanical processes interact with fault heterogeneity under controlled injection conditions, with direct access to well-characterized and densely instrumented fault zones. Previous characterization of the target MC fault zone at BedrettoLab show that layers of frictional velocity-strengthening (VS) fault gouge are embedded within velocity-weakening (VW) granitic bare rock, forming a strongly heterogeneous frictional architecture. However, how this frictional partitioning controls fault slip behavior and the magnitude of induced seismicity remains unclear. In this study, we use the newly developed 3D hydro-mechanical model HydroMech3D to explore the interplay between frictional heterogeneity and seismicity in fluid injection simulations, governed by rate- and state-dependent friction. We simulate injection scenarios using parameters and conditions derived from the ongoing FEAR (Fault Activation and Earthquake Rupture) experiments at Bedretto. Our simulations investigate how the spatial distribution of VS and VW patches control seismicity magnitude. By systematically changing the partition of VS and VW patches, we explore its influence on event size distributions and maximum magnitudes. Further simulations are conducted under various hydro-mechanical pre-conditioning conditions, by pre-determining the pressurized patch on the fault via the injection protocol prior to the main injection. These simulations allow us to understand whether fault pre-conditioning may influence the maximum magnitude of induced seismicity. Our results emphasize the critical role of frictional heterogeneity and injection strategy in fault dynamics, providing new insights into the hydro-mechanical behavior of complex fault zones during fluid injection and improving seismic risk assessment and mitigation strategies.
How to cite: Ye, J., Wang, Z., Ciardo, F., Rinaldi, A. P., Dal Zilio, L., and Giardini, D.: 3D Modeling of fluid-induced seismicity on fault with heterogeneous frictional asperities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17827, https://doi.org/10.5194/egusphere-egu26-17827, 2026.
Fluid injection associated with geoenergy applications such as geothermal energy, CO2 sequestration, and hydraulic fracturing can alter fault stability through a combination of coupled hydro-mechanical processes. Laboratory experiments and underground observatories have provided valuable constraints on fault friction and near-fault pressure evolution, yet translating these observations to field-scale behavior requires physics-based numerical models that can resolve fault slip under realistic geometrical and mechanical conditions.
A major limitation of existing modeling approaches is the high computational cost of fully coupled three-dimensional simulations. As a result, many studies rely on one-dimensional fault representations or simplified elastic and hydraulic coupling. While such models have provided important insights into key physical mechanisms, they are not well suited to support the design, interpretation, and long-term forecasting of modern injection experiments equipped with dense monitoring systems. These experimental settings increasingly demand three-dimensional models capable of capturing realistic fault geometry, spatially variable frictional and hydraulic properties, and stress interactions beyond reduced-dimensional assumptions.
Here we present HydroMech3D, a physics-based numerical framework designed to efficiently simulate fluid-driven fault slip over earthquake-cycle timescales in three dimensions. The model employs a quasi-dynamic Boundary Element Method, discretizing only the fault surface embedded in elastic medium, thereby avoiding volumetric meshing. Fault slip is governed by rate-and-state friction and coupled to pore-pressure diffusion along the fault. Computational efficiency is achieved through a C++ implementation accelerated by hierarchical matrix from the Bigwham Library, enabling large-scale simulations with realistic fault geometry.
This framework allows systematic investigation of fault-scale heterogeneity, including asperities with contrasting frictional and hydraulic properties, and provides a platform to explore how three-dimensional fault structure influences aseismic slip, stress transfer, and earthquake nucleation during fluid injection. Benchmarking against established earthquake-cycle test cases validates the mechanical solver and establishes a baseline for ongoing fully coupled simulations. HydroMech3D offers a computationally efficient open-source tool to support experiment design, interpretation of near-fault observations, and assessment of induced seismicity in geoenergy applications.
How to cite: Wang, Z., Dal Zilio, L., Ciardo, F., and Rinaldi, A.: HydroMech3D: physics-based earthquake-cycle modeling of fluid-driven fault slip with realistic fault geometry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8716, https://doi.org/10.5194/egusphere-egu26-8716, 2026.
Accurate simulation of injection-induced seismicity requires to solve for strongly coupled hydro-mechanical physics describing processes acting over widely separated spatiotemporal scales, ranging from reservoir scale fluid diffusion to fault nucleation and rapid dynamic rupture. In this study, we present a monolithic hydro-mechanical dynamic framework based on the extended finite element method (XFEM) for modeling fluid-induced fault reactivation governed by rate-and-state friction. Faults are represented as embedded displacement discontinuities within a poroviscoelastic medium, enabling a consistent treatment of fault slip, unilateral contact constraints, stress-dependent permeability evolution, and fluid exchange between the fault and the surrounding porous matrix.
To overcome the computational cost associated with fully implicit time integration, we develop a hybrid implicit–explicit (IMEX) time-integration strategy. The implicit solver is employed during the quasi-static and nucleation phase, while an explicit scheme is activated only during the coseismic stage, once a prescribed slip-velocity threshold is exceeded. This adaptive solver switching allows accurate resolution of the dynamic rupture with substantial reduction of the computational effort. The approach is combined with adaptive time stepping to efficiently capture both slow interseismic evolution and fast seismic transients within a unified framework.
Numerical simulations of fluid injection into a faulted reservoir demonstrate that, despite unconditional stability, fully implicit schemes require minimum time steps comparable to the Courant–Friedrichs–Lewy limit to accurately resolve rupture nucleation and propagation. In contrast, the proposed IMEX formulation can reproduce fault slip evolution, stress redistribution, frictional weakening, seismic moment, and event magnitude with high fidelity, while reducing computational cost by approximately 60–77% relative to fully implicit simulations. Differences between the two approaches are primarily limited to peak slip velocities and rupture speeds, whereas rupture timing, accumulated slip and event-scale seismic metrics remain consistent.
The proposed XFEM-based IMEX framework provides a robust and computationally efficient tool for simulating injection-induced seismicity, offering a practical pathway toward reservoir scale simulations of coupled fault–fluid systems relevant to geo-energy applications and seismic hazard assessment.
How to cite: Sabah, M., Cacace, M., Hofmann, H., Blöcher, G., Reza Jalali, M., and R. Kivi, I.: A Hybrid Implicit–Explicit XFEM Framework for Fully Coupled Hydro-Mechanical Dynamic Simulation of Injection-Induced Seismicity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17977, https://doi.org/10.5194/egusphere-egu26-17977, 2026.
Anthropogenic activity in the subsurface causes stress perturbations which can lead to the onset of seismicity. One of the notorious examples is the Groningen gas field in the northeast part of the Netherlands which is among the largest in Europe. Hydrocarbons have been produced there since 1963 until the field’s ultimate shutdown in October 2023. From December 1991 until January 1st, 2026, total of 1561 events have been recorded in this area, with magnitude ranging from to . The events caused extensive damage to buildings and quite a societal unrest as well as scepticism towards subsurface operations in general. Considering, it is crucial to identify an envelope for safe utilization of the subsurface to be able to continue its usage for energy transition while limiting the risk of induced seismicity.
To be able to limit the risk of seismicity from subsurface operations, it is necessary to understand the non-stationary nature of induced seismicity, meaning the underlying physical causes of the observed spatial and temporal variations in event locations and frequency-magnitude distribution. This research is based on the hypothesis that the fault spatial distribution and geometry (dip angle, offset) in conjunction with operational parameters (pressure history, rates, injection temperatures) are the causal processes of the temporal and spatial variations in the Gutenberg-Richter parameters.
I will present the results from modelling production induced seismicity using the Groningen field as a study area. The results include synthetic earthquake catalogues obtained by modelling the event nucleation and magnitudes using a semi-analytical approach of slip weakening faults. For this model, fault geometry and pressure history serve as input. In order to obtain multiple catalogues spanning the full range of uncertainty, a Monte Carlo sensitivity analysis is conducted for different reservoir and fault properties. Subsequently, several statistical comparison tests of the simulated catalogue with the observed seismicity allows us to derive posterior estimates for our properties and provide crucial insight into how we are doing solving the puzzle of what is causing the observed spatiotemporal behaviour of induced earthquakes.
How to cite: Dvornik, L., Muntendam-Bos, A., Jansen, J. D., and Buijze, L.: Understanding the Non-Stationary Nature of Human-Induced Earthquakes and its Impact on Geothermal Energy Production, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17447, https://doi.org/10.5194/egusphere-egu26-17447, 2026.
The prediction of induced seismicity is a critical challenge for geological risk management and the safe operation of industrial facilities, such as geothermal projects. This study focuses on the Cooper Basin in Australia. We applied data science and machine learning techniques to analyze seismic time series, integrating two data sources: discrete seismological events (23,285 events) and continuous operational data sampled every 2 minutes (33,839 records).
The main objective was to develop machine learning models to predict, in future time windows of 10, 30, 60, and 90 minutes, two key variables: the number of seismic events or the maximum magnitude. The XGBoost and Random Forest algorithms were trained and compared. Model performance was evaluated using the R², RMSE, and MAE metrics, and their interpretability was analyzed using SHapley Additive exPlanations (SHAP).
The results demonstrate that both models generate predictions consistent with the observations, showing better predictive performance in the longer time windows (60 and 90 minutes). This approach provides a valuable framework for the monitoring and proactive risk assessment of geothermal operations.
How to cite: Garay Romero, L. R., Faenza, L., Garcia-Aristizabal, A., and Lombardi, A. M.: Application of Data Science and Machine Learning Techniques for the Prediction of Induced Seismicity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12815, https://doi.org/10.5194/egusphere-egu26-12815, 2026.
Cold fluid injection into a hot subsurface reservoir alters the in situ temperature, pore pressure, and stress fields through multiple interacting physical mechanisms. Poroelastic stress changes arise from pressure diffusion, whereas thermomechanical stresses are driven by reservoir cooling and associated thermal contraction. In this study, we investigate how hydraulic anisotropy in the reservoir controls the spatio-temporal evolution of these stress perturbations and related failure potential. We present results from fully coupled thermo-hydro-mechanical (THM) simulations using a three-dimensional reservoir-scale generic model, considering different injection scenarios, including single injection wells and doublets, as well as isotropic and anisotropic hydraulic properties. In general, both temperature and pore pressure variations affect the radial and tangential stress components relative to the injection site in distinct ways, even under isotropic material conditions. This distinction is critical for evaluating slip tendency and calculating Coulomb failure stress changes (ΔCFS) for the faults in the vicinity of the injection well. For anisotropic reservoir conditions, we compare the temporal evolution of pore pressure and temperature during single-well injection against isotropic reference cases and assess the implications for ΔCFS. For 20 years of continuous injection and permeability anisotropy factor of 10, the temperature front propagates approximately 20 times faster along the high-permeability direction. While the rate of pressure diffusion scales with the permeability component in the direction of propagation, the resulting pressure magnitude is governed by permeability components in the perpendicular directions. Similarly, thermally induced stresses evolve more rapidly in high-permeability directions and more slowly in low-permeability directions, as well as producing different magnitude changes in radial and tangential stress components. The modeled ΔCFS indicates that although fault orientation influences the calculated stress changes, the dominant control arises from directional fluid flow associated with hydraulic anisotropy. In conclusion, hydraulic anisotropy exerts a first-order control on the spatial and temporal distribution of pressure and temperature perturbations, leading to pronounced directional variations in induced stress fields and the corresponding Coulomb failure stress evolution in the vicinity of geothermal boreholes. These results provide a basis for optimized drill site selection and well orientation strategies aimed at minimizing fault reactivation and reducing the risk of injection-induced seismicity.
How to cite: Sharia, T., Müller, B., and Rietbrock, A.: Stress perturbations and fault reactivation during cold fluid Injection - impact of hydraulic anisotropy , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16611, https://doi.org/10.5194/egusphere-egu26-16611, 2026.
The increasing occurrence of injection-induced earthquakes has raised public concern and highlighted the importance of understanding subsurface processes to assess induced seismic hazards and risks. A feature of natural faults that has not received sufficient attention in induced seismicity modeling is their geometric roughness. We develop a simple physics-based model to investigate how fault roughness can control induced seismicity during fluid injection.
The first approach to modeling along-fault stresses prior to injection is to project the background stress tensor onto the rough fault. In this case, our models and theoretical analysis show that the apparent diffusivity of seismicity fronts can deviate significantly from the hydraulic diffusivity. Faults with realistic roughness generally display slow seismicity migration, producing apparent diffusivities far below the hydraulic values. Thus, seismicity fronts often lag behind the pressure front, especially at low background stresses and small roughness amplitudes. Only in the rare case of very rough faults stressed very close to failure, apparent diffusivity can exceed the hydraulic diffusivity, leading to seismicity fronts that outpace pressure fronts.
The second approach to modeling along-fault stresses prior to injection is to simulate stress evolution after multiple tectonic rupture cycles. This ongoing work explores the resulting stress heterogeneity after multiple tectonic rupture cycles and examines whether seismicity migration follows the same trend as in the first approach, i.e., whether seismicity migration is generally slower than the pressure front on rough faults.
Apart from seismicity migration, the magnitude-frequency statistics are also analyzed. Along this single rough fault the frequency-magnitude distribution is bimodal. These results demonstrate how fault roughness and stress conditions control the induced seismicity through their influence on the criticality of the fault and stress transfer, and link long-term fault loading processes with short-term seismicity migration patterns in fluid injection scenarios.
How to cite: Lin, H.-F., Candela, T., and Ampuero, J.-P.: Injection-induced seismicity fronts and stress distribution on rough faults, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9772, https://doi.org/10.5194/egusphere-egu26-9772, 2026.
In 2017, an MW 5.5 earthquake struck the Pohang region, representing the most damaging seismic event in South Korea, and has been linked in previous studies to hydraulic stimulation at the Pohang Enhanced Geothermal System (EGS) site. However, the relative roles of fluid injection, imposed stress state and fault-zone structure in nucleating this event remain a matter of debate, and the laboratory results presented here are intended to illuminate one mechanically plausible scenario rather than provide a unique causal explanation. Despite the scientific and societal importance of this earthquake, the frictional properties of rocks from the Pohang system are still poorly constrained. Here we experimentally characterize the frictional properties and slip behavior during fluid-induced reactivation of granodiorite wall rock powder and fault gouge recovered from the Pohang PX-2 borehole (~3.8 km depth). We first assessed the mineralogical assemblages of the two fault materials, which consist of mixtures of quartz, K-feldspar, plagioclase and phyllosilicates (mostly chlorite), with phyllosilicate contents varying between 15% and 23% for the wall rock and the fault gouge, respectively. We then measured friction, healing rate and the velocity dependence of friction for both materials under water-saturated conditions at normal stresses of 20–100 MPa using the BRAVA apparatus hosted at the National Institute of Geophysics and Volcanology (INGV). We performed frictional experiments in a double-direct-shear configuration, using a protocol consisting of a run-in at 10 µm/s, slide-hold-slide tests (SHS; hold times ranging between 3 and 3000 s), velocity-stepping tests (VS; velocities ranging between 0.3 and 300 μm/s), and fluid-injection tests (pore-pressure increases of 0.25 MPa every 5 min). Steady-state friction coefficients for both materials fall within the Byerlee range (μ ≈ 0.55–0.62). SHS tests reveal that both fault gouge and wall rock exhibit relatively high healing, with β in the range ≈ 0.0046–0.0092. Conversely, velocity-stepping tests reveal that, over the tested stress and velocity range, the wall rock has a slightly velocity-weakening to neutral behavior (a–b = −0.0007 to 0.0020), while fault gouge is predominantly velocity-neutral to strengthening (a–b = 0.0005 to 0.0028). Additional fluid-injection experiments indicate that, despite these slight differences in frictional properties, both the fault gouge and the wall rock can be reactivated under elevated pore pressure, with slip accelerating from creep to millimetre-per-second rates. Accompanying microstructural observations will examine whether differences in grain-size reduction, shear localization, or porosity evolution account for the similar reactivation behavior despite the slightly contrasting frictional properties. Overall, these measurements will help quantify how lithological heterogeneity, rate-and-state parameters, and pore-pressure evolution govern slip stability and the nucleation potential of injection-induced earthquakes in geothermal settings, with important implications for induced-seismicity hazard assessment in granitic EGS reservoirs.
How to cite: Woo, S., Volpe, G., Coppola, L., Collettini, C., and Son, M.: Frictional properties and fluid-induced reactivation of fault rocks from a granitic EGS reservoir, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12316, https://doi.org/10.5194/egusphere-egu26-12316, 2026.
