Seismic tremor signals were recorded in 2021 by a temporary broadband seismic network deployed in the surroundings of the Domo de San Pedro geothermal field (DSPgf) in Mexico. A network-based covariance matrix approach was used to analyze those tremor-like signals, employing vertical-component data only. Seismic tremors were detected by identifying periods associated with low values of spectral width, defined as the width of the eigenvalue distribution of the network covariance matrix. These tremors occur in frequency bands ranging from 1 to more than 22 Hz, with durations varying from hours to months, and show higher amplitudes at closest stations to the active wells. The spectral characteristics of the DSPgf tremor-like signals reveal similarities to those found in volcanic and glacial environments, such as the presence of harmonic frequencies and spectral gliding. The sources of these tremor signals are located by back-projecting on a 3-D grid the dominant component of the wavefield obtained from the covariance matrix first eigenvector. Tremor locations indicate that the events originate within the zones of influence of the wells where geothermal operations occurred. We categorized four distinct tremor families based on spectral width signatures and compared them with detailed operational records. Our findings reveal that tremors at the DSPgf are associated with geothermal operations such as fluid extraction, wellbore maintenance, fluid re-injection, and changes in injection pressure. We propose a conceptual model of the first order tremor-generating mechanism for each tremor family.

How to cite: Muñoz-Burbano, F., Soubestre, J., Savard, G., Calò, M., Reyes-Orozco, V., and Ávalos, D.: Monitoring induced seismic tremor associated with fluid injection/extraction and mechanical operations at the Domo San Pedro geothermal field (Mexico), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19407, https://doi.org/10.5194/egusphere-egu25-19407, 2025.

Underground gas storage (UGS) systems are commonly used to balance seasonal fluctuations in demand and to secure strategic reserves by storing gas in geological trap formations. All underground industrial activities, including UGS, can affect the pore pressure and pre-existing stress state in seismogenic layers, potentially triggering earthquakes. Monitoring microseismicity in such a context is crucial, especially in urban areas. The study area of this work focuses on the Cornegliano Laudense UGS site, near Milan, one of 15 such sites in Italy, where the National Institute of Oceanography and Applied Geophysics (OGS) conducts seismic monitoring. In 2017, nine seismic stations were installed in accordance with national guidelines to establish a baseline of natural seismicity before the start of gas storage activities in December 2018.

Previous studies have shown that the central sector of the Po Plain has weak and deep seismicity due to crustal shortening between the Alpine and Apennine fronts. However, shallow seismicity has occasionally been recorded since monitoring began. Shallow seismicity was recorded both before and after the onset of storage activities, suggesting that it may be related to shallow tectonic structures. At the end of September 2024, the local seismic network detected its first seismic sequence, consisting of nine shallow microearthquakes with magnitudes between 0.9 and 1.3 ML and a depth of ~ 2.5 km. These seismic events occurred near a known thrust fault just outside the storage area.

We present preliminary results of a seismicity analysis performed to understand the origin of these shallow microearthquakes. Detection and location of such small earthquakes is challenging due to their low magnitude and low signal-to-noise ratio in this area. To improve detection, we applied a template matching technique based on the cross-correlation of continuous seismic data with well-located events, known as templates. This process revealed more than 150 seismic events throughout the entire monitoring period, with magnitudes ranging from -1 to 1.6 ML. Initially assigned to the locations of their templates, the hypocenter locations were refined by identifying P and S wave arrival times, where possible, applying both absolute (NonLinLoc) and relative (HypoDD) location methods. Our analysis also identified small clusters of past seismic events like those in the September 2024 sequence using a template matching method. For each sequence, we calculated composite focal mechanisms using the SKHASH code, combining polarities and S/P amplitude ratios for more reliable results. Finally, we examined seismicity diffusion patterns to assess potential fluid movement influences, as seismic events triggered by fluid intrusion often show characteristic spatial and temporal migration patterns.

How to cite: Fusco, M., Guidarelli, M., Romano, M. A., Sugan, M., Romanelli, M., Sandron, D., and Picozzi, M.: Application of methodologies for the analysis of microseismicity in industrial areas: a case study from underground gas storage in Cornegliano Laudense, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9387, https://doi.org/10.5194/egusphere-egu25-9387, 2025.

For the transition to a low-carbon future, carbon capture and storage (CCS) is a field of intense research worldwide. However, the process needs to be monitored closely for induced seismicity, and this in turn requires a clear picture of the background seismicity of the immediate area around the storage site. This study focuses on assessing the background seismicity of the Gulf of Kavala in Greece, where an offshore CCS pilot is deployed within EU project COREu. However, a major challenge associated with this area is the scarcity of catalogued events due to its low seismicity, as well as the sparse seismic station distribution, owing also to geography. To overcome this challenge, in this study, state-of-the-art AI-based seismic detectors (EQTransformer and PhaseNet) are used to re-evaluate existing recordings and enrich the area’s catalogue with low-magnitude events. A two-stage approach is considered to take into account and resolve the particularities of this involved task. In the first stage, we evaluate the baseline performance of the adopted pre-trained AI-based detectors, using data from the Corinth Gulf area, selected because the seismic network there is significantly denser and the seismicity higher. Specifically, for our purposes, we used data from a microseismic sequence of more than 400 events recorded in the first half of 2021, with magnitudes ranging from 0.1 to 1. In the experiment we utilize recordings of the selected events from a total of 50 stations located around the seismic sequence, with distances out to several tens of kilometers, to build a dataset with a wide and representative range of recording SNRs. To assess the detectability of the events, for each event/station pair, we measure the output of the detectors in a time-window of 5 seconds around the event arrival, forming a (detector) response magnitude vs SNR curve. This is used as a guideline for determining a detection threshold that strikes a good balance between true and false positives. Through this successful application of the method in the Corinth Gulf area, we gained significant knowledge about the limitations and the necessary configuration of the methods. In the second stage of the study, we conduct a preliminary detection experiment on continuous recordings from Prinos, utilizing data from stations surrounding the target area. The outcome of this experiment is evaluated by expert seismologists, using a specially created visualization tool for assisting the evaluation process. The adopted two-stage approach leads to the detection of a considerable number of low-magnitude, previously undetected events, constituting a significant first step towards assessing the implementation of CCS  in the Prinos area.   

How to cite: Pikoulis, E.-V., Mavrokefalidis, C., Ktenidou, O.-J., and Sokos, E.: AI-assisted assessment of low-magnitude seismicity in the area of Kavala-Prinos (Greece) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20161, https://doi.org/10.5194/egusphere-egu25-20161, 2025.

Large fluid volume injections into the subsurface are increasingly common across a range of industrial and remediation activities. However, deep fluid injections are often associated with increased seismicity within a few hundred kilometers of the injection sites. The role of aseismic slip as an important precursory signal in induced-seismicity has gained importance in the community due to two reasons: (a) the time and length scales of injection-induced earthquakes are inconsistent with realistic diffusivities, and  fluid-transport models do not match observations, and (b) modern theories of fault weakening suggest that at very high fluid pressures, faults can experience aseismic slip for prolonged periods before ultimately transitioning to unstable, seismic failure driven by static stress transfer.

Our work investigates far-field microseism triggering in NE Texas and NW Louisiana within the Haynesville shale-gas field that has developed since 2008. It includes  the 2012 Mw 4.8 Timpson, TX earthquake, which has been attributed to wastewater injection. Seismicity from a temporary array and national monitoring show an increase in the number and magnitude of earthquakes in the area, with regular ML3 events near the Texas-Louisiana border. InSAR data indicate uplift around some injection wells. We consider multiple injection wells and compute the spatial distribution of geodetic strain rates derived from GNSS velocities and compare them with seismic strain rates from new earthquake data. In the decade following the 2012 event, several microseisms across the Texas-Louisiana border have been recorded, suggesting that critically stressed faults in the vicinity are being triggered in part by static stress transfer, as well as newer injection wells.  We compare fault orientations to current stress, consider Coulomb stress change from the Timpson event, and use fluid transport models to explain the seismicity and vertical land motion observed in the Haynesville Shale play area.

How to cite: Arzabala, E., Sarma, P., Hurtado-Pullido, C., Musila, M., and Ebinger, C.: Fluid-Induced Aseismic Slip: Far-Field Triggering and Static Stress Transfer in the Haynesville Shale Gas Field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3844, https://doi.org/10.5194/egusphere-egu25-3844, 2025.

The Western Canada Sedimentary Basin (WCSB) covers a vast area, extending from a zero edge along the Canadian Shield to the Canadian Cordillera in the west, where the basin is up to 7 km thick. Seismicity is largely concentrated within a ≈300km wide corridor, immediately east of the deformation front of the Canadian Cordillera. The northern half of the WCSB experiences natural earthquakes in the Mackenzie and Richardson Mountains, which are strongly influenced by plate-boundary interactions along the west coast of North America. To the south, seismicity in northeastern BC and western Alberta is characterized by localized induced (human-caused) seismic activity related to unconventional resource development during the last 15 years. This north-south partitioning of seismicity is reflected in Canada’s national seismic hazard maps, which consider only natural seismic hazards and highlight areas of relatively elevated seismic hazard in the Mackenzie and Richardson Mountains. However, since 2021 the seismic moment-release rates have become broadly similar in both southern and northern regions of the WCSB, despite relative seismic quiescence in the south from 2000 – 2014. Short-term seismic hazard maps for Alberta show localized areas of elevated seismic hazard that track temporarily and spatially varying levels of industry activity. The advent of large-scale carbon capture and storage (CCS) and geothermal projects could increase the potential for anthropogenic triggering of seismic activity.

How to cite: Eaton, D., Kao, H., Canales, M., and Shipman, T.: The big picture in western Canada: Induced seismicity from geo-energy applications is approaching the natural moment release rate of tectonically active northern regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20644, https://doi.org/10.5194/egusphere-egu25-20644, 2025.

Monitoring induced seismic harzards during the fluid injections has been a significant challenge for geo-energy development. Conventional approaches, such as the (adaptive) traffic light protocol and prediction methods based on statistical and machine learning regressions, often yield limited accuracy due to diverse geological conditions across regions. A promising direction lies in developing precursors to monitor fault reactivation more effectively.

Recent seismological studies have shown that aseismic slip loading is more prevalent than previously thought during fault activation induced by fluid injections (Yu et al., 2021a, b; Eyre et al., 2019, 2022). Slow earthquake signals, like Earthquakes characterized by Hybrid-frequency Waveforms (EHW), occur during the transition from fault creep to brittle rupture induced by fluid injection (Guglielmi et al., 2015). These signals are potential indicators for aseismic slip loading and fault reactivation. However, their longer rupture durations distinguish them from typical induced earthquakes, rendering classic source analysis methods ineffective for real-time monitoring.

To address this limitation, we propose ASTF-Net, a machine learning (ML) model designed to predict Apperant Source Time Function (ASTF) by deconvoluting Empirical Green's Function (EGF) waveform from target waveform in time domain. This approach provides reliable real-time estimates of source durations, to identify slow earthquake signals, specifically EHW, and offers a valuable tool for fault activation monitoring. A robust and well-sampled dataset is therefore crucial for the model's performance.

In this study, we present a dataset designed for developing a single-channel version of ASTF-Net and evaluate its effectiveness using basic ML-models. The dataset consists of three parts: ASTFs, EGFs, and target seismic waveforms. Synthetic ASTFs are generated using kinematic forward modeling with an elliptical rupture model to simulate earthquake events with magnitudes ranging from Mw 3.0 to 4.5 and stress drops between 5 and 20 MPa. These random ASTFs are calculated under various ray paths. We collect EGFs from hydraulic fracturing-induced earthquakes (M1.5-2.5) in the Southern Montney Play, western Canada, recorded by a network of 40 nodal/broadband seismic stations between 2017 and 2020. Synthetic target waveforms are then created by convolving ASTFs with corresponding EGFs. The dataset’s inputs consist of single-channel synthetic seismic waveforms and their corresponding EGFs, with ASTFs as outputs. To assess the generalization and robustness of the model, records from different stations are divided into training, validation, and four test sets with varying difficulty levels based on geographical locations and event counts. Notably, Test level 4 is human analysis results reported by Roth et al. (2022).

We evaluate model performance using basic ML architectures, including MLP, CNN, VGG and U-Net. Performance metrics include the Correlation Coefficient (CC) between predictions and labeled ASTFs, and the relative error in apparent source duration. CNN emerges as the most promising candidate for the further optimization, achieving the following CC > 0.9 across test levels: 87.9% (Level 1), 85.9% (Level 2), and 80.3% (Level 3). The percentages of relative error below 10% are 59.3%, 59.3%, and 51.2%, respectively, for the three levels.

How to cite: Pang, R., Yu, H., Li, G., Meng, H., Liu, Z., Su, C., Zha, D., and Tian, W.: Dataset preparation for Resolving Apparent Source Time Functions (ASTF) and Evalutions Using Basic ML-models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7718, https://doi.org/10.5194/egusphere-egu25-7718, 2025.

The spatial distribution of hydraulic fracturing-induced seismicity is controlled by regional tectonics and local geological structures. In this study, we integrated a high-resolution shear velocity model from ambient noise imaging with 3D seismic reflection data to investigate structural influences on induced seismicity near an active hydraulic fracturing (HF) platform in the Sichuan Basin, China. We conducted continuous seismic monitoring throughout the fracturing period and located over 1,000 earthquakes within the 7 weeks of active stimulation. Tomographic model reveals a distinct first-order, EW-striking velocity boundary near the HF well. This lateral velocity discontinuity aligns closely with the 3D curvature attribute identified in seismic reflection data, with high-curvature areas corresponding to disrupted geological features like small-scale faults or stratigraphic discontinuities. Further quantitative analysis reveals that in addition to the spatial clustering near high-curvature areas, 70% of earthquakes are distributed on the high-velocity side and concentrated within a range of 500 meters from the HF well. Based on these observations, we infer that 1) the high-velocity anomalies are mechanically stronger and more susceptible to the release of cumulative elastic energy, and 2) pronounced attribute variations delineate the principal seismogenic structures responsible for hosting induced earthquakes. Consequently, regions with brittle rock properties and significant structural variations are more seismically sensitive under external fluid injection. Future work will involve applying the ETAS model to better understand the triggering mechanisms of induced seismicity, aiming to provide insights into the interaction between external fluid injection and localized stress perturbations.

These observations highlight the interplay between velocity heterogeneity, structural attributes, and localized stress perturbations in driving induced seismicity. Similar correlations between local velocity structure and earthquake nucleation are observed at a nearby platform, where the majority of over 6000 detected earthquakes are preferentially located near a NE-SW oriented high-velocity structure east of the injection well. Interestingly, both platforms are characterized by sharp topographic relief, with their maximum gradient well aligning with the velocity boundaries. These integrated structural features may prove crucial in identifying local geological structures that are prone to instability and assist strategy development toward risk mitigation of HF-induced seismicity.

How to cite: Zhang, F., Chen, Y., Wang, R., Yu, H., Rinaldi, A. P., and Ritz, V.: Structural Controls on Earthquake Clustering in Hydraulic Fracturing: Insights from Velocity Model and Seismic Reflection Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7395, https://doi.org/10.5194/egusphere-egu25-7395, 2025.

Seismicity induced by water reservoir and fluid injection are widely known phenomena and have been studied for several decades. However, seismicity induced by crustal unloading in large open-pit mines are seldomly reported in the literature. Here we describe a case of seismicity associated with the large open-pit Cajati mine in SE Brazil, which has been operating for more than 40 years. The mine exploits carbonate rocks of a Mesozoic alkaline intrusion complex. The pit is 1.4 km long and 0.75 km wide reaching 300 m depth. The estimated amount of extracted rock is about 350 Mton. Nine earthquakes with magnitudes in the range 2.0-3.2 Mw have been recorded since 2009 by stations of the Brazilian Seismic Network (RSBR), some of them felt with intensities IV MM in nearby towns. The 2015 mainshock (3.2 Mw) caused expressive cracks in the mine benches, with up to 10 cm displacement. Epicenter relocation of the six largest events, using correlated P- and S-waves at regional distances, show that all events occurred in a single NNW-SSE oriented, 0.5 km long rupture aligned with the major axis of the pit, in agreement with the main trend of the micro-seismicity recorded by the local mine network. Focal mechanism was determined with two techniques: ISOLA envelope and FMNEAR using three stations at 100 to 160 km distance. Both methods show a reverse faulting mechanism with nodal planes oriented NW-SE to NNW-SSE.  This is consistent with the expected mechanism for crustal unloading in open-pit mines. The Cajati mine is located in the Ponta Grossa Arch, in the coastal ranges of SE Brazil, a region with low-velocities at lithospheric depths. This suggests lithospheric thinning that concentrates stresses in the upper crust. In addition, the NE-SW P axis orientation is parallel to the coast line, a pattern that favors concentration of the regional stresses due to continental/oceanic structural transition. Aeromagnetic data shows a clear NNW-SSE regional fault crossing the mine area. The Cajati mine-induced seismicity is a classic case where several positive factors contribute to the inducing mechanism: a) high stresses in the upper crustal, b) favorable orientation of a previously existing weak zone (related to the NNW-SSE fault during emplacement of the alkaline body), and large Coulomb stress changes of about 4 MPa from unloading of the vertical stresses.

How to cite: Assumpcao, M., Schirbel, L., Nogueira, J. A., Carvalho, J., Dias, L., and Bianchi, M.: Seismicity Induced by a Large Open Pit Mine in SE Brazil: Combination of Stress Concentration and Crustal Weakness., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4842, https://doi.org/10.5194/egusphere-egu25-4842, 2025.

Triggering of earthquakes due to the filling of dam reservoir is attributed to mechanical disequilibria, build-up by pore pressure diffusion driven differences in deformation and stresses in the subsurface rocks, ultimately compensated by the reactivation of faults. This kind of earthquake, also known as Reservoir induced seismicity (RIS) has the characteristics of small magnitude, high intensity, shallow source and long period. In some cases, seismic activities have lasted for several decades after the initial impoundment (e.g. in Koyna-Warna, India). Various approaches have been made by researchers to comprehend the role of water reservoirs in triggering such unique events.  Modeling fluid-induced earthquakes requires coupling geomechanics, flow through porous media, and fault friction. A 2D poroelastic finite element model has been employed, incorporating coupled pore fluid diffusion and stress analysis along with contact interaction coupled to rate-and-state friction law, to simulate the stress change, deformation in rocks and fault slip due to reservoir impounding. Rate-and-state friction has been used with an aim to develop a modelling framework that can capture multiple earthquake sequences in order to understand the protracted RIS phenomenon. A fault is embedded in a 2D subsurface domain as contacting surfaces, the frictional behaviour along the fault surfaces is prescribed using a user subroutine FRIC in ABAQUS/Standard. The rate-and-state law has been defined in the subroutine. The ability of the subroutine to simulate multiple events of stick-slip motion has been checked using a simple spring-block slider analogy. The fault model is first initialised by simulating the in-situ field conditions, geostatic stresses are defined in the domain, frictional contact at the fault is established and zero pore pressure conditions are defined. After which, reservoir loading is applied on the top surface of the domain over a transient consolidation step and the pore pressure evolution down at the fault is studied. The decrease in fault strength is a result of increase in pore pressure that reduces the effective normal compressive stresses. The stress path, accumulated slip and friction coefficient at the midpoint of the fault is observed. The fault remains locked at the beginning, while the effective normal stress continues to decrease, at a point the fault strength drops and it starts to slip. Friction coefficient increases at the onset of slip, which is known as the direct effect, then decreases as the slip accelerates. Later, the fault rupture is arrested and the friction coefficient goes back to a higher value gradually. While simulating rupture in the fault, the contact interaction undergoes chattering when the fault slips abruptly, causing simulation to fail. In a non-dynamic analysis, instabilities will occur as the strain energy released due to fault slip cannot be dissipated. Contact damping has to be specified to dissipate the released energy. In the present study, only one event of fault slip has occurred. Increase in the pore pressure near the fault due to reservoir loading is not high enough for a second slip event.

Keywords: Reservoir Induced Seismicity, Poroelasticity, Rate and State Friction, Fault Slip

How to cite: Chakraborty, A., Gautam, S. S., and Dey, A.: Modeling Reservoir-Induced Seismicity using Rate-and-State Friction law , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19220, https://doi.org/10.5194/egusphere-egu25-19220, 2025.

A three-dimensional quasi-dynamic finite element method is developed to simulate fluid-induced seismicity on faults governed by rate-and-state friction. The coupled nonlinear hydro-mechanical equations governing both the fault and the surrounding rock matrix are solved simultaneously using the Imperial College Geo-mechanics Tool (ICGT), providing fluid pressure and displacement fields. This work highlights enhancements made to the friction module of ICGT, specifically the implementation of the augmented Lagrangian method to enforce fault surface contact constraints. This approach leverages the strengths of both the penalty method and Lagrange multipliers within the finite element framework. A stick-predictor slip-corrector algorithm is developed for the rate-and-state friction law to improve the convergence of the solution. The proposed numerical model captures the dynamic response of a fault to fluid injection, with the fault represented explicitly as a zero-thickness interface element in the mesh. To account for radiation damping effects and prevent unbounded slip rates within the quasi-dynamic framework, a velocity-dependent cohesion term is introduced into the shear stress formulation. The results emphasize the importance of selecting appropriate spatial mesh sizes and temporal time steps to ensure the convergence of the iterative Newton-Raphson solver. The simulation results show that pore pressure changes initiate an aseismic slip front that propagates along the fault, leading to failure in seismogenic zones. This method successfully captures all stages of the seismic cycle, including the transition from stick to slip behavior. 

How to cite: Hosseini, N., Paluszny, A., and Zimmerman, R. W.: Fluid-Driven Slip on a Three-Dimensional Fault with Rate-and-State Friction: A Finite Element Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6205, https://doi.org/10.5194/egusphere-egu25-6205, 2025.

The connection between fluid pressure, reservoir permeability evolution, slow-slip events, and the triggering of larger earthquakes remains a crucial but unresolved issue in the study of fluid-induced seismicity. Understanding these interactions is essential for seismic hazard mitigation and optimizing subsurface fluid injection productivity.

Discrete Fracture Networks (DFNs) are commonly used to study hydraulic diffusion and seismic activity within fault systems. However, traditional DFN models often rely on quasi-static assumptions and a simple Mohr-Coulomb criteria for earthquake triggering. These limitations hinder their ability to capture dynamic phenomena, such as self-propagating slow-slip events, and they provide little insights into the earthquake dynamics.

This study  addresses these gaps by developing a 2D DFN model capable of simulating both fluid-induced slow-slip events and the potential for earthquake triggering. The model integrates hydraulic diffusion and slip processes governed by rate-and-state friction across several interacting faults within an impermeable, elastic rock matrix. A key innovation of this model is the dynamic evolution of fault permeability, which depends on normal traction changes and accumulated slip, consistent with laboratory and in-situ experiments.

The model was applied to two scenarios, both with and without permeability evolution: (1) fluid injection along a primary rough, rate-strengthening fault, where slow slip events occur and subsequently triggers microseismicity on secondary, smaller faults; and (2) fluid injection within a network of rate strengthening intersecting faults, where fluid diffusion reactivates slip throughout the network. In both cases, the simulated slow-slip events propagate faster than the fluid pressure diffusion front.

Interestingly, the migration patterns of microseismicity in the first case and slow slip in the second resemble diffusion processes, yet exhibit diffusivity values distinct from the imposed fault’s hydraulic diffusivity. This finding suggests that estimates of hydraulic diffusivity based solely on microseismicity front migration may not be accurate, in line with previous experimental and modeling studies.

These results highlight the influence of variable permeability and stress transfer caused by slow slip transients, offering valuable insights into induced seismicity within crustal reservoirs.

How to cite: Romanet, P., Scuderi, M. S., Ampuero, J.-P., and Cappa, F.: Impact of variable permeability in fault networks on fluid-induced seismicity dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5744, https://doi.org/10.5194/egusphere-egu25-5744, 2025.

Earthquakes that occur during geothermal exploitation or any other fluid-injection activity (hydraulic fracturing, CO2 waste disposals…) are attributed to the reactivation of rapid slip along critical faults. This highlights the urgent need of comprehensive monitoring and mitigation strategies to ensure both energy production and environmental safety.

Our main objective is to develop numerical methods to infer the permeability enhancement during fault reactivation induced by fluid injection in the laboratory. To this end, we model an experimental protocol conducted on a rock sample with a saw-cut fault, led by F.X. Passelègue and collaborators from the EPFL and GéoAzur rock mechanics laboratories. At the beginning of the injection experiments, pore pressure was uniformly set to 10 MPa along the fault plane. The injection experiment was preceded by a loading phase, during which shear stress was increased to approximately 90% of the peak shear stress to bring the fault to a critically pre-slip state. Fluid was then injected along the fault at a constant rate of 1 Mpa/minute, with simultaneous measurements of pore pressure, slip, and shear stress recorded continuously.

To simulate the experimental process, we established a system of coupled partial and ordinary differential equations that describe the evolution of key variables, including permeability, porosity, fault slip, and pore pressure. These equations are solved numerically. The general behavior of our key variables generated by the model reproduces the trend observed in the data recorded in the laboratory. For an advanced data match we develop a deterministic inversion approach, specifically the adjoint state method, to infer the permeability model. We are currently focused on enhancing this inverse model.

How to cite: Ben Khaled, I., Dublanchet, P., Chauris, H., Passelegue, F., and Blanco Martin, L.: Inferring Permeability Enhancement During Fluid-Induced Fault Slip Reactivation In The Laboratory, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16675, https://doi.org/10.5194/egusphere-egu25-16675, 2025.

Fluid injection-induced earthquakes present a significant challenge for geo-energy applications, such as geothermal systems and CO2 storage. Understanding the earthquake magnitude and frequency in response to fluid injection is of vital importance. Both the pressure and pressure rate are considered dominant parameters for the occurrence of induced earthquakes. Theoretical analyses of a spring-block model [1] have demonstrated that the reservoir response depends on the nondimensional pressure rate, defined as the ratio of the characteristic time of frictional slip to that of pressurisation. The pressure rate effect is most pronounced when this ratio falls within a narrow range of 10-4 to 10-3. These results have contributed to the interpreting laboratory experimental observations, however, the correlation between the injection rate and induced earthquakes at the field scale remains poorly understood.
This work develops a coupled hydro-mechanical model to simulate constant-rate fluid injection into a reservoir adjacent to a sealing, steeply-dipping, rate-and-state frictional fault, aiming to evaluate fault activation behaviour and the associated induced earthquake magnitude and frequency. The fault is modelled as a rate-and-state frictional contact with Mohr-Coulomb fault strength, and deemed to be reactivated when the shear traction on the fault exceeds the fault strength (frictional resistance), which depends on the fault sliding velocity. Rate-and-state fault slip dynamics are resolved using frictional contact modelling through a fully implicit, monolithically coupled finite element formulation. The fault is characterised by velocity-weakening frictional properties, allowing it to slip multiple times during fluid injection. A seismicity rate model is used to simulate the induced seismicity rate along the fault during fluid injection. Given that the nondimensional pressure rate depends on both the critical slip distance (related to the characteristic time of frictional slip) and the injection rate (related to the characteristic time of pressurisation), different combinations of the two parameters within the typical range of field values are examined to investigate the pressure rate effect on induced earthquake magnitude and frequency and seismicity rate.
Results have shown that the critical slip distance affects both the magnitude and frequency of induced earthquakes, whilst the injection rate primarily controls the frequency of induced earthquakes in typical field conditions. Notably, the induced earthquake frequency, along with the induced seismicity rate, shows a positive correlation with the pressure rate. However, the maximum induced earthquake magnitude does not appear to be significantly affected by the pressure rate within the typical range of field conditions. Based on the model results, the range of nondimensional pressure rate, within which the pressure rate effect is significant in field reservoir conditions, is identified. Outcomes of this work may provide valuable guidance for regulating injection rates to mitigate fluid injection-induced earthquakes in geo-energy applications.

Reference
[1] Rudnicki, J.W. and Zhan, Y., 2020. Effect of pressure rate on rate and state frictional slip. Geophysical Research Letters, 47(21), p.e2020GL089426.

How to cite: Cao, W. and Ma, T.: Pressure rate effect on the fluid injection-induced earthquake magnitude and frequency, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5080, https://doi.org/10.5194/egusphere-egu25-5080, 2025.

Injection-induced earthquakes (IIEs) are commonly attributed to pore-pressure elevation and associated Coulomb stress changes, leading to widespread adoption of Traffic Light Systems (TLS) that primarily focus on injection rate modulation for hazard mitigation. However, recent field observations have identified aseismic slip as an alternative mechanism for fault reactivation during direct fault-zone fluid injection, with evidence showing that slip propagation can outpace fluid migration fronts. Despite these insights, the critical conditions that determine when aseismic slip becomes the dominant mechanism—particularly the role of injection parameters—remain poorly understood. Here, we present direct fault-injection experiments equipped with high-resolution monitoring of fault slips and fluid difussions. Our findings reveal two fundamental insights into IIE mechanisms: (1) When faults are subjected to specific combinations of injection rates and pre-stress conditions, aseismic slip can initiate and propagate beyond the fluid-pressurized zone, becoming the primary mechanism for IIEs. (2) In near-critically stressed faults, the maximum seismic moment release may remain elevated even after injection rate reduction, undermining a core assumption of TLS protocols. Overall, these observations highlight that fault stress conditions, rather than injection parameters alone, dictate the upper bound of seismic hazard. 

How to cite: Wang, C., Wang, P., and Xia, K.: How Does Injection Rate Control Injection-Induced Earthquakes?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19763, https://doi.org/10.5194/egusphere-egu25-19763, 2025.

There is still uncertainty in the mechanisms controlling the increase in earthquake productivity and shale gas development in the southern Sichuan basin of China. In this study we take advantage of a more complete seismic catalog from local seismic stations, as well as injection data for two adjacent hydraulic fracturing wells, during March 2017 to January 2018, to investigate these mechanisms. To ensure the completeness and reliability, two seismic catalogs were effectively merged and uniformly scaled using the moment magnitude M_w scale. A spatiotemporal constraint framework was designed to extract induced earthquakes during the injection stages, and a series of seismic statistical methods were used to study the correlation between 885 earthquakes (M_w 0 to 4.6) and fluid injection. These include the ETAS model, and the nearest-neighbor-distance method. The results suggest most seismicity close to the wells are likely linked to the hydraulic fracturing process. For events associated with the N5 well pad, the cumulative number of earthquakes has a positive correlation with the cumulative injection volume. Through the use of the Seismogenic-Index, the difference of seismogenicity of different wells is obtained. We show that injected volume not only correlates with the number of induced earthquakes, but also correlate with the maximum seismic magnitude in the region. We demonstrate that this can then be used to retroactively forecast the induced seismicity. Although the injection at the  two well pads is similar, the N5 pad is associated with many more indued events compared to the N7 pad. Reflection seismic imaging indicates that faults and fractures are well developed beneath the target reservoir of N5, but not for N7. This indicates proximity to preexisting faults/fractures control the occurrence of inducing seismicity in the region. The possible cause of the M_w 4.6 earthquake is briefly analyzed by calculating the range of pore pressure diffusion, and the Coulomb stress change from poroelastic effects. This shows that induced seismicity in the southern Sichuan basin is controlled by both preexisting faults/fractures and injection fluid volume.

How to cite: Hu, J.: The productivity of induced seismicity in the southern Sichuan basin, China is controlled by injected volume and preexisting faults , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13985, https://doi.org/10.5194/egusphere-egu25-13985, 2025.

The world's energy supply depends critically on hydraulic fracturing (HF): HF operations utilize microseismicity to enhance subsurface permeability, so that hydrocarbons or geothermal heat can be extracted economically.  Unfortunately, HF also has the potential to induce larger earthquakes – with some projects being prematurely terminated because of perceived earthquake risks.  To de-risk HF, we use a suite of novel statistical tests called CAP-tests to discern if some physical process has restricted the growth of earthquake magnitudes.  We show that all stage stimulations at UK PNR-1z indicate bound fracture growth, implying a more controllable operation.  Contrastingly, stimulations at Utah FORGE and UK PNR-2 sequentially transitioned into unbound fault reactivation.  The problematic stages (that ultimately led to the termination of PNR-2) are clearly distinguishable using CAP-tests.  We postulate that our research can discriminate fracture stimulation from fault reactivation, contributing to the de-risking of HF operations worldwide.

How to cite: Schultz, R., Lanza, F., Dyer, B., Karvounis, D., Fiori, R., Shi, P., Ritz, V., Villiger, L., Meier, P., and Wiemer, S.: The bound growth of induced earthquakes could de-risk hydraulic fracturing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-110, https://doi.org/10.5194/egusphere-egu25-110, 2025.

Induced seismicity related to industrial operations including carbon storage, geothermal energy, hydraulic fracturing or wastewater disposal has become increasingly common over the last 15 years. To continue these operations with minimal impact on sites, populations and economic conditions of the operation, it is crucial to better understand the mechanisms that control induced earthquakes and the occurrence of these in both space and time.

This research focuses on enhancing statistical forecasts (using the seismogenic index model and ETAS), specifically for CO2 storage applications. This forecasting is essential for estimating the hazards associated with the operational life cycle of these sites. Additionally, based on these forecasts, we explore operational management strategies, aimed at providing real-time feedback and suggestions to operators. All model calibrations were performed using data from the Illinois Basin Decatur Project – a pilot CO2 storage initiative with injection performed from 2011 to 2014. The resulting forecasts are included within an ensemble forecast within the open-source Operational Forecasting of Induced Seismicity (ORION) toolkit.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

How to cite: Geffers, G.-M., Wang, C., Sherman, C. S., and Kroll, K. A.: Statistical Models to Forecast Induced Seismicity in CO2 Storage , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11791, https://doi.org/10.5194/egusphere-egu25-11791, 2025.