PICO
This session calls for contributions that showcase novel methodologies and/or ambitious case studies. Topics of interest include, but are not limited to:
- Advances in stress orientation and magnitude estimation
- New methodologies for 3D geomechanical modelling, including deterministic, stochastic, hybrid approaches or stress state visualisations
- Outstanding case studies highlighting crustal stress characterisation, fault stability, and/or the application of geomechanical modelling
- Advances in computational efficiency and uncertainty quantification
- Innovative use of machine learning and AI in enhancing models and approaches
This session brings together geoscientists, modellers, and computational experts from an academic and application background to discuss the latest advancements and challenges, offering insights into the future direction of characterizing the present subsurface stress state.
The analysis of earthquake focal mechanisms is a key tool for studying active tectonic deformation. Various stress inversion methods are frequently used based on this data to obtain stress tensors by making a series of assumptions that can compromise the reliability of the results. On the other hand, obtaining seismic deformation tensors from the summation of seismic moment tensors offers a solid alternative for characterising seismic strain tensors without the uncertainties inherent in stress-based approaches. In this work, we study the global distribution and shape of these combined seismic strain tensors, with special emphasis on their geometric properties and non-double-couple (NDC) components. Our results show systematic patterns in the shape of the tensor in different tectonic contexts. Shallow seismicity, predominantly associated with plate boundaries, shows alternating ellipsoid shapes between prolate and oblate along oceanic ridges, while subduction zones show planar-type strains (near the double-couple) in interface events and departures from this double-couple in back-arc zones. In contrast, deep seismicity within subduction slabs shows greater variability, with some slabs characterised by oblate ellipsoids and others by prolate geometries, indicating diverse deformation modes at depth. Continental collision zones, such as the Himalayan front and the Zagros belt, are dominated by oblate tensor shapes, while adjacent regions, such as the Tibetan plateau, exhibit prolate geometries, reflecting a significant component of uniaxial extension or constriction. Error estimation is addressed through probabilistic weighting of focal mechanisms based on uncertainties in event location and through a Monte Carlo perturbation scheme of the tensor components. This characterisation of aleatory errors ensures a robust evaluation of eigenvalues, eigenvectors, and parameters derived from them. The observed correlation between the tensor shape and the tectonic context highlights the usefulness of strain tensor-based approaches for seismotectonic studies. By characterising instantaneous seismic strain, the methodology proposed in this work complements the study of both brittle and ductile finite strain. These results contribute to improving global models of lithospheric deformation and show the importance of incorporating the geometry of seismic strain tensors into tectonic and geodynamic analysis, as well as their potential application to seismic risk.
How to cite: Alvarez-Gómez, J. A., Alonso-Henar, J., and Sánchez-Roldán, J. L.: Application of seismic strain tensor shape analysis to global tectonics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12678, https://doi.org/10.5194/egusphere-egu26-12678, 2026.
This study presents a novel iterative method for inverting regional stress fields from focal mechanism data. Building upon key techniques in homogeneous stress inversion, the method enhances the accuracy of stress estimation. The procedure involves clustering seismic events based on spatial distribution to define discrete stress domains, followed by fault plane identification via a fault instability criterion, thereby relaxing the conventional assumption of uniform shear stress across all planes. Stress continuity between adjacent domains is imposed to ensure a smoothly varying stress field. The method is applied to both synthetic tests and earthquake data from the seismically active Sichuan–Yunnan region of China. Results demonstrate that, while principal stress orientations remain consistent with those obtained from conventional approaches, the proposed method provides more reliable estimates of the stress shape ratio, which align more closely with the regional tectonic framework.
How to cite: Guo, X. and Li, Z.: An Improved Method for Inverting the Spatiotemporal Stress Field Using Focal Mechanism Data and Its Application in Sichuan–Yunnan Region, China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4589, https://doi.org/10.5194/egusphere-egu26-4589, 2026.
Characterization of the in-situ state of stress is critically important in many geoscience applications, including understanding fault mechanics. In-situ stresses can exhibit strong spatial heterogeneities, due to the influence of factors such as surface topography, slip along faults and fractures, as well as lithological contrasts. Our understanding of these factors has been limited by our inability to characterize the full stress tensor and its variability at high spatial resolution. Additionally, studying the relationship between fault mechanics and the heterogeneous stresses has been prevented by the lack of in-situ observations of fault slip in rock volumes well-characterized in terms of stress. The FEAR project provides a unique opportunity to tackle these gaps in our knowledge. As part of this project, a series of hydraulic stimulation experiments are performed in a fractured granitic rock mass intersected by major faults in ETH’s BedrettoLab. The induced seismicity and hydromechanical processes are monitored using a dense sensor network.
To characterize the stress field in the rock mass of interest, a detailed hydraulic fracturing campaign was performed in three vertical and eight inclined boreholes. We developed a new stress inversion method that can infer an arbitrarily inclined primary stress tensor from hydraulic fracturing tests performed in arbitrarily inclined boreholes. The method uses a grid search approach to invert the generalized Kirsch Solution and allows us to quantify the uncertainty of the solution (i.e. its sensitivity to error in the measured input data) both in terms of principal stress magnitudes and orientations. The required input data are fracture orientation from image logs, shut-in pressure, breakdown and fracture reopening pressure.
Applying our inversion technique to the data collected in the BedrettoLab resulted in 32 stress tensor solutions (including uncertainty) corresponding to different locations within the rock volume, as well as 14 additional data points of the S3 magnitude. Our results show that S3 is (sub-)horizontal in the entire rock volume, and its azimuth ranges from N147.8 to 211.4°E. The rock mass can be divided into two domains based on the stress regime: a normal faulting domain in the SSE portion of the rock volume and a strike-slip faulting domain in the NNW portion. Potential causes for the observed abrupt transition from normal to strikes-slip faulting may be compliance contrasts within the rock volume as well as fault slip along different geological structures. The normal faulting domain extends a few meters into the northern side of a major, SSW-ENE oriented fault, and it is unclear whether the transition is related to this fault.
Our high-resolution stress dataset will enable us to investigate the causes of the observed stress heterogeneity using numerical modeling tools, and to determine which faults are likely to slip and open during hydraulic stimulations. Once available, the experimental data of hydraulic stimulations will be compared to our predictions. This will provide an unprecedented opportunity to study the relationship between in-situ stresses and fault dislocation, ultimately resulting in an improved understanding of earthquake physics in general.
How to cite: Kövér, B., Gischig, V., Bröker, K., Aaron, J., Meier, M.-A., Hertrich, M., Giardini, D., and Wiemer, S.: Characterization of stress heterogeneity around a fault zone based on inversion of hydraulic fracturing tests , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7235, https://doi.org/10.5194/egusphere-egu26-7235, 2026.
Accurate in situ stress characterization is essential for predicting the subsurface response to interventions such as underground construction, fluid injection, and fluid extraction. At depths of 2–5 km, which are typical of many such projects, the stress field is often heterogeneous and influenced by complex geological features. This makes reliable stress measurement both operationally critical and technically challenging. Borehole stability is another key concern, as deep boreholes are prone to stress-induced deformations such as breakouts that can damage equipment, impede drilling, and even lead to borehole collapse.
We present results and ongoing developments from two projects focused on novel in situ stress measurement techniques and thermo-hydro-mechanical processes around boreholes. These projects are based on experiments conducted at the Bedretto Underground Laboratory (BedrettoLab) in Switzerland (Ma et al., 2022). The BedrettoLab offers multiple boreholes, up to 400 m in length, located within a fractured granitic rock mass with an overburden of more than 1000 m.
The first project developed an improved technique to estimate the full stress tensor by inverting three-dimensional displacement data obtained during fluid injections in isolated borehole intervals (Bröker et al., 2025). A total of eleven test intervals were investigated, with displacements measured using a SIMFIP (Step-rate Injection Method for Fracture In situ Properties) probe. The results yield a complete stress profile obtained along approximately 60 m of an inclined borehole, revealing significant stress heterogeneity and rotations around an intersected fault zone.
In the second project, we developed a novel borehole probe to investigate the formation of thermally induced breakouts, which are strongly controlled by the in situ stress field. The probe can heat a packed-off borehole section while measuring borehole wall displacement. After extensive calibration in the laboratory, the probe was deployed in the BedrettoLab, and three in situ heating tests were successfully conducted up to 140 °C. Although no borehole breakouts were induced, the experiments provide valuable insight into thermo-hydro-mechanical coupling at borehole walls and its role in breakout initiation and borehole stability.
References:
Bröker, K., Guglielmi, Y., Soom, F., Cook, P., Hertrich, M., & Valley, B. (2025). In situ quantification of fracture slip induced by hydraulic injections in a deep borehole: A comparison of two different borehole techniques. Submitted to IJRMMS. https://doi.org/10.2139/ssrn.5967430
Ma, X., Hertrich, M., Amann, F., Bröker, K., Gholizadeh Doonechaly, N., Gischig, V., Hochreutener, R., Kästli, P., Krietsch, H., Marti, M., Nägeli, B., Nejati, M., Obermann, A., Plenkers, K., Rinaldi, A. P., Shakas, A., Villiger, L., Wenning, Q., Zappone, A., et al. (2022). Multi-disciplinary characterizations of the BedrettoLab – a new underground geoscience research facility. Solid Earth, 13(2), 301–322. https://doi.org/10.5194/se-13-301-2022
How to cite: Bröker, K., Valley, B., Hertrich, M., Dutler, N., Steiner, P., Soom, F., Cook, P., and Guglielmi, Y.: New borehole-based techniques for in situ stress measurement and related thermo-hydro-mechanical processes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17493, https://doi.org/10.5194/egusphere-egu26-17493, 2026.
The motion and deformation of the lithosphere result from forces and stresses that are driven by lateral variations in gravitational potential energy (GPE). In turn, GPE variations derive from lateral differences in the thermal or lithological density distribution. The recent development of global lithospheric models allows us to take a step forward towards consistent estimates of Horizontal Gravitational Tractions (HGTs) that arise from lateral gradients in GPE. We find that lithospheric model LithoRef18 [Afonso et al. 2019] yields unrealistic GPE and HGT results. Our preferred HGT field uses lithosphere model WINTERC-G [Fullea et al. 2021] to incorporate horizontal GPE gradients with a laterally variable Lithosphere-Asthenosphere Boundary (LAB). The azimuth of HGTs is most strongly correlated with the azimuth of topographic gradients, while the HGT magnitudes correlates best with topography gradient magnitude for HGTs larger than 10MPa. The most significant HGT magnitudes, exceeding 100 MPa, occur along the edges of the Andes and Tibetan plateaus. Tractions in cratonic regions are generally low, except where surface, Moho, or LAB topology gradients are large. Our attempt to isolate the HGT of the overriding plate yields moderate oceanward HGTs in the forearc along all convergence zones, which may be interpreted as trench suction. We explore the sensitivity of the HGT to classical integration limits of the deepest Moho or 100km depth to find that HGT magnitudes are markedly different and that HGT directions are relatively insensitive to integration depth.
Afonso, J.C., Salajegheh, F., Szwillus, W., Ebbing, J. Gaina, C. (2019), A global reference model of the lithosphere and upper mantle from joint inversion and analysis of multiple data sets, Geophys. J. Int., 217(3), 1602–1628.
Fullea, J., Lebedev, S., Martinec, Z., Celli, N.L. (2021), WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical–petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data, Geophys. J. Int., 226(1), 146–19.
How to cite: Nijholt, N., Gutierrez Escobar, R., Wouters, M., and Govers, R.: Lithospheric Driving Forces From Recent Global Density Models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12437, https://doi.org/10.5194/egusphere-egu26-12437, 2026.
Deformation of the Earth’s crust is fundamentally governed by subsurface stress and pore fluid pressure, which together define effective stress as the difference between total stress and pore pressure. Effective stress controls a wide range of processes, such as fluid migration, sediment compaction, subsidence, fault reactivation and the earthquake cycle. It is also a key parameter for the design of subsurface engineering such as drilling operations, fluid and heat production as well as storage of CO2, radioactive waste, hydrogen and energy. For the safe exploration and operation of georeservoirs and for the development of mitigation strategies of induced hazard such as borehole failure, leakage due to fault reactivation, or induced seismicity a reliable quantification of the effective stress is essential.
Over the past four decades, subsurface horizontal stress orientations and, more recently, stress magnitudes have been systematically compiled and analysed using dedicated quality-ranking schemes. The data are publicly available through the World Stress Map (WSM) database. In contrast, pore pressure data remain fragmented and inconsistently documented. Where available, pore pressure information is typically dispersed across national, regional, commercial or private databases, as well as scientific publications and technical reports. Publicly accessible pore pressure databases are rare and generally lack standardised formats or the application of a common quality assessment. Furthermore, although pore pressure measurements have been collected since the early development of deep drilling primarily by the petroleum industry, most datasets have not been published due to confidentiality concerns. Consequently, pore pressure information is often limited to isolated case studies or regional analyses that neither provide digital data nor precise spatial referencing.
As a result, a global database with quality-ranked pore pressure data complementary to the WSM does not yet exist. This absence represents a major limitation for both fundamental geoscience research and practical application in reservoir management required for a sustainable energy future. To address this gap, this contribution aims to initiate the development of a global database using a quality-ranking scheme for direct pore pressure measurements and indirect pore pressure indicators. The proposed open-access resource referred to as the World Pressure Map is intended to combine data from different methods to make them comparable and to ensure long-term data availability.
How to cite: Shatyrbayeva, I., Duschl, F., Breitsameter, J., Ziebarth, M. J., Heidbach, O., Müller, B., and Drews, M. C.: Towards a global and quality-ranked pore pressure magnitude database - World Pressure Map, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12818, https://doi.org/10.5194/egusphere-egu26-12818, 2026.
Over the past many decades, in-situ stress measurement using overcoring (OC) and hydraulic fracturing (HF) methods has been scientifically accepted and commercially adopted worldwide as the benchmark techniques for quantifying in-situ stress in rock masses. However, with the increase in depth of mining operations, the application of OC and HF has become more cumbersome and costlier, requiring substantial drilling, specialized equipment, and favorable borehole conditions for reliable data collection. This paper investigates the potential of non-destructive techniques (NDTs) for in-situ stress estimation as practical alternatives to conventional methods. A structured comparison of the non-destructive techniques including AE, Deformation Rate Analysis (DRA), Secant Modulus Method (SMM) is presented with the conventional OC and HF methods based on the published literature. To validate these techniques further, non-destructive tests were conducted on oriented rock cores retrieved from a mine site in South Australia where conventional overcoring had been previously applied. The SMM and AE analyses were used to determine the stress tensor and magnitude & direction of principal stresses. The results show a good correlation with the OC data, reinforcing the reliability of NDTs of stress estimation. These findings suggest that integrated non-destructive methods can provide cost-effective alternatives to traditional in-situ stress measurement techniques, offering significant implications for deep mining projects and early-stage stress characterization where borehole access is limited.
How to cite: Ali, Z., Karakus, M., and D. Nguyen, G.: A Comparative Study of Conventional and Non-Destructive Methods of In-Situ Stress Measurement, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8840, https://doi.org/10.5194/egusphere-egu26-8840, 2026.
Determination of in situ stress magnitude and orientation is fundamental for understanding crustal mechanics and facilitating subsurface exploration and development as well as hazard assessment. At present, in situ stress at depth is mainly estimated from borehole observations. Traditional methods, such as hydraulic fracturing tests, are mature and practical, yielding reliable estimates of the least principal stress but usually at a limited number of depths. Estimates of the maximum horizontal stress (SHmax) and stress orientation rely on observations of compressive or tensile failure of the borehole but can have considerable uncertainty depending on borehole conditions. Therefore, new approaches to estimate in situ stress magnitudes effectively are desired in stress characterization.
In this study, we extend a novel approach for stress determination that utilizes the natural fractures identified in deep boreholes. Critically-stressed natural fractures exhibit distinct thermal anomaly identifiable on temperature logs, whereas non-critically stressed fractures do not. Given an abundant and diverse set of natural fractures, inversion is feasible to estimate the magnitude of the maximum and minimum horizontal stresses utilizing the knowledge of the vertical stress (estimated from density logs).
We illustrate this novel approach with the KTB borehole data set. The classification facilitated a two-stage stress inversion that efficiently inverts the in situ stress orientation and absolute magnitude. The inverted stress matches well with independent borehole observations. The maximum discrepancy between the inversion results and the SHmax derived from wellbore failures is 26.6 MPa at 7 km depth, which is lower than the uncertainty of estimated SHmax magnitude (~47 MPa). The inverted SHmax orientation is N161.3°E, which is quite consistent with the observed SHmax orientation obtained from wellbore failures (~N160°E). To investigate stress heterogeneity over finer scales, the inversion was also applied to selected subsets of fractures along the KTB borehole. We evaluate the limitations and scale-dependence of this approach by considering the fracture distribution and fault perturbations. Our results demonstrate that profiling in situ stress via natural fractures is feasible and complementary to existing approaches, and can offer new insights on the characteristics of crustal stress, its spatial heterogeneity, and its interactions with geological discontinuities.
How to cite: Ma, X., Wang, H., and Zoback, M.: Novel crustal stress profiling based on the criticality of natural fractures – a KTB example, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2549, https://doi.org/10.5194/egusphere-egu26-2549, 2026.
The Earth’s crust is a mechanically heterogeneous system in which stress, fractures, and geofluids are tightly coupled and jointly control deformation. Quantifying the present-day crustal stress state remains challenging, as it is commonly inferred from indirect and spatially sparse observations and often relies on simplifying assumptions in seismic imaging and mechanical models.
We present a methodological framework that combines probabilisitic anisotropic seismic imaging with geomechanical modeling to constrain the crustal stress state in a physically consistent manner. Seismic anisotropy in the upper crust, expressed through directional variations in elastic properties, is used as a proxy for fracture orientation, fracture density, and fluid-induced compliance, which are intrinsically linked to the ambient stress field. Incorporating anisotropic parameters into seismic imaging reduces inversion artifacts and enables a more robust characterization of stress-aligned fracture networks.
These seismic constraints are integrated into geomechanical models that simulate the stress field under realistic boundary conditions and rheological properties, and calibrated by direct comparison between observed stress indicators (e.g. seismic T-axes, surface faulting patterns, fast shear wave polarisations), anisotropy patterns and model-predicted stress orientations. This combined approach improves stress-state quantification by leveraging seismically-inferred 3D fracture patterns while also providing a framework to assess uncertainties arising from seismic imaging assumptions and mechanical parameter choices.
The proposed methodology is broadly applicable to tectonic and volcanic settings, as well as geothermal and oil fields, and offers a transferable strategy for improving stress-state estimates in regions where direct measurements are limited.
How to cite: Faccenda, M., VanderBeek, B. P., and Del Piccolo, G.: Crustal stress state from combined anisotropic seismic imaging and geomechanical modeling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5185, https://doi.org/10.5194/egusphere-egu26-5185, 2026.
Intersecting normal faults that depart from ideal Andersonian orientations in a rapidly extending rift, subject to both orthogonal and rotational opening as well as magmatic activity, generate complex patterns of stress interaction. We investigate these processes in the Wairakei Geothermal Field, the oldest and largest electricity producer within the Taupō Rift, Aotearoa New Zealand. There, boreholes show pervasive fracturing both near faults and in intervening blocks. We developed three-dimensional forward finite element models (FEM) with the Adeli open-source code which accounts for elasto-visco-plastic behaviour (pressure dependent Drucker-Prager plasticity and temperature dependent viscosity). We simulate far-field extension applied on a simplified crustal scale, synthetic fault system consistent with the structural settings. Three steeply dipping (70°) pre-existing faults are set mechanically weaker than the surrounding bedrock. One fault aligns with Andersonian strike, while two intersecting faults are misoriented by –15° and +30°.
Modeled fault displacements and stress rotations broadly agree with paleoseismic slip rates and with the limited but clear stress rotations observed in geothermal boreholes. Preliminary results provide indicators to explain enhanced crustal permeability and the exceptionally productive Wairakei Geothermal Field : zones of strain localisation where fracturing concentrates; stress ratio reflecting how faults behave kinematically with respect to the applied regional stress field; domains undergoing stress rotations and creating conditions where fractures of various orientations become optimally oriented for slip and dilation, most pronounced in domains within 1 km of the pre-existing faults.
Alternating boundary conditions between orthogonal and oblique rift extension (representing rotational rift opening or nearby magma deflation) further enhances the opening of fractures of different orientations at different times. We also tested the influence of the main faults dip and relative strength on resulting slip and dilation tendencies patterns.
This approach provides new insights into stress evolution in magmatic rifts, with implications for seismic and volcanic hazard assessment and for improving the targeting of permeable zones in geothermal reservoirs.
How to cite: Gerbault, M., Massiot, C., Ellis, S., and Villamor, P.: Modeling Stress and Deformation Near Intersecting Misoriented Normal Faults in the Taupō Rift, Aotearoa New Zealand: A New Approach to Target Geothermal Permeability?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2731, https://doi.org/10.5194/egusphere-egu26-2731, 2026.
Subsurface exploration for geoenergy resources within the seismically-active Lower Rhine Graben (LRG) in the cross-boarder region of Belgium, Germany and the Netherlands (NW Europe) needs to consider the tendency for induced seismic events as well as the effect of subsurface operations to the present-day crustal stresses. Regionally, geomechanical investigations are challenged by inconsistent coverage of reliable geologic and stress data below the Tertiary Rhineish lignite deposits. As deep geothermal exploration is currently focused entirely below these formations within marine sediments from Lower Carboniferous to the Devonian period, a first order 3D regional stress model to seismogenic depths up to 10 km is developed using a newly compiled 3D structural geological model combining data from three national datasets of the cross-boarder region. The structural geological model is distilled to a parameterized FEM mesh and used as input for numerical simulations of crustal stresses based on linear elasticity theory using the open-source MOOSE framework. Calibration of the resulting geomechanical model is completed using focal mechanisms from seismic catalogues, borehole failure observations, and hydraulic fracturing tests in boreholes within the LRG. 3D geomechanical model results of the LRG region provide a quantitative footing to support deep geothermal development through a spatially-continuous characterization of in situ stresses, even in greenfield prospects with little to no stress information, and an improved assessment of the reactivation potential of major faults in the region targeted for future geothermal development.
How to cite: Jones, A., Kruszewski, M., Ziegler, M., and Amann, F.: 3D Geomechanical Model of the Lower Rhine Graben in the Cross-Boarder Region (BE–DE–NL), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7920, https://doi.org/10.5194/egusphere-egu26-7920, 2026.
Characterizing the crustal stress state and its spatial variability is essential for the safe and sustainable development of structurally controlled deep geothermal systems. The seismically active Lower Rhine Graben (LRG), spanning parts of Germany, Belgium, and the Netherlands, is a promising target for geothermal exploitation in fault-controlled, karstified carbonate reservoirs of Lower Carboniferous and Devonian age. However, at drillable depths, the stress field remains poorly constrained, raising concerns regarding fault reactivation and induced seismicity, as highlighted by moderate induced events at recent deep geothermal projects in Belgium and the Netherlands.
We present a quality-rated crustal stress database for the LRG and adjacent regions, integrating legacy and newly acquired stress indicators from earthquakes and recently drilled exploratory boreholes. Stress tensor inversion was performed using recent earthquake focal mechanisms, while borehole-based indicators from hydraulic fracturing tests and borehole deformation analyses provided direct constraints on stress orientations and absolute stress magnitudes at reservoir-relevant depths. These data were combined with publicly available present-day stress indicators from existing databases, and interpolated onto a regular 0.1° grid to generate a gridded stress field capturing regional-scale, long-wavelength variability.
The spatially variable stress field was integrated with mapped major faults to evaluate their reactivation potential by assigning stress orientations to individual fault segments. Our results indicate a clockwise rotation of the maximum horizontal stress from WNW–ESE in the Hohe Venn area west of the graben to NNW–SSE in the Rhenish Massif to the east. At geothermal reservoir depths, NW–SE-striking normal faults show elevated potential for shear reactivation and dilation, whereas NE–SW-striking thrust faults exhibit low potential for both mechanisms.
By integrating more than 135 stress indicators into a spatially resolved fault reactivation analysis, this study substantially increases stress data coverage in the region and provides quantitative constraints on fault stability and seismic hazard relevant for geothermal development, supporting site selection and risk-informed reservoir management in the tectonically active LRG.
How to cite: Kruszewski, M., Jones, A., Verdecchia, A., Carrasco Morales, S., Oswald, T., Harrington, R., and Amann, F.: Crustal Stress Field Variations and Fault Reactivation Potential in the Lower Rhine Graben and its Adjacent Regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18531, https://doi.org/10.5194/egusphere-egu26-18531, 2026.
Geomechanical modeling aims to predict the 3D in-situ stress state of the Earth’s crust and to assess the stability of subsurface rock volumes for applications such as radioactive waste disposal, energy storage, or CO₂ geo-sequestration. However, model calibration typically relies on sparse in-situ stress magnitude data which are expensive to acquire, limited in spatial coverage, and may not represent stress conditions over larger rock volumes, away from the measurement sites. Here we present a probabilistic forward-calibration framework that uses the borehole failure interpreted from routinely acquired borehole-image logs as indirect stress data and formation integrity tests (FIT) to calibrate 3D geomechanical models.
Our approach integrates four types of indirect stress observations: the occurrence of borehole breakouts (BO), drilling-induced tensile fractures (DITF), formation integrity tests (FIT), and the documented absence of both BO and DITF at micro-hydraulic fracturing (MHF) stations. Although these indirect data provide only upper and lower limits on the stress state, they offer the critical advantage of scanning the entire borehole trajectory with high resolution, yielding far more extensive spatial coverage than point measurements. The absence of borehole failure provides simultaneous upper and lower bounds on horizontal stress magnitudes, addressing a key limitation in previous approaches that struggled to constrain the maximum horizontal stress magnitude. We developed a forward uncertainty quantification framework that explores hundreds of thousands of model scenarios at each observation point using linear elastic principles and compares the agreement between predicted and observed stress indicators through a probabilistic assessment.
In the Zürich Nordost siting region for a potential deep geological repository for radioactive waste in northern Switzerland, we leverage an exceptional stress magnitude dataset from two deep boreholes. This dataset comprises 30 high-quality microhydraulic fracturing tests and 15 dry sleeve reopening tests, accompanied by comprehensive borehole image logs and detailed laboratory measurements of Young's modulus and rock strength. Using the stress magnitude data alone to calibrate the geomechanical model yields accurate stress predictions with well-constrained uncertainties, providing a rigorous benchmark against which to evaluate models calibrated solely with indirect stress indicators.
Our results demonstrate that stress predictions based solely on indirect observations achieve comparable accuracy to those calibrated with an exceptionally large and robust dataset of in-situ stress magnitude data. For the magnitude of the minimum horizontal stress Shmin, high-agreement scenarios reproduce the reference stress predictions throughout most of the stratigraphic section, with uncertainties dominated by natural rock property variability rather than stress magnitude uncertainty. For the magnitude of the maximum horizontal stress SHmax, the approach successfully delivers constrains within physically realistic ranges, though systematic overestimation of 2–3 MPa in some formations suggests remaining model limitations. This work demonstrates that indirect stress data, readily available during routine drilling operations, can provide reliable, uncertainty-quantified stress predictions without requiring expensive in-situ stress measurement campaigns, opening new possibilities for stress field characterization in subsurface projects worldwide.
How to cite: Laruelle, L., Ziegler, M. O., Heidbach, O., Velagala, L. S. A. R., Reiter, K., Giger, S., Rajabi, M., Degen, D., and Cotton, F.: Geomechanical model calibration in the absence of in-situ stress magnitude data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13001, https://doi.org/10.5194/egusphere-egu26-13001, 2026.
Accurate quantification of the subsurface stress state, and of its resolved components on faults and fractures, is critical for de-risking applications ranging from geothermal energy and subsurface storage to nuclear waste disposal. While the governing mechanics are well established—reactivation depends on resolved normal and shear stresses, pore-fluid pressure, and frictional resistance—practical barriers remain to accessible, reproducible tools for 3D stress-state visualisation and systematic evaluation of stress–structure interactions.
We present PyFracTend, an open-source Python implementation of the MATLAB-based workflow developed by Stephens et al. (2018), packaged with a cross-platform graphical user interface (GUI) to support reproducible analysis in both research and applied workflows. PyFracTend takes as input principal stress magnitudes and orientations (3D), pore-fluid pressure, and fault/fracture orientation datasets (azimuth and dip), together with user-defined mechanical parameters (e.g., coefficient of friction and cohesion, where applicable). The toolbox computes commonly used stability indicators—including slip tendency, dilation tendency, and related measures—and visualises results on stereonets and Mohr diagrams. All inputs and outputs are exported as analysis-ready tables, enabling straightforward integration with third-party software and downstream modelling.
To ensure consistency with established practice, we benchmark PyFracTend against the original MATLAB implementation, demonstrating agreement across representative stress states and discontinuity datasets. Finally, responding to the growing need for uncertainty-aware stress characterisation, PyFracTend integrates seamlessly with the pfs Python code (Healy & Hicks, 2022) for uncertainty quantification (e.g., Monte Carlo sampling of stress tensor parameters), thereby propagating stress uncertainties into probabilistic fault/fracture stability metrics.
References:
Stephens, T. L., Walker, R. J., Healy, D., Bubeck, A., & England, R. W. (2018). Solid Earth, 9, 847–858.
Healy, D. and Hicks, S. P. (2022). Solid Earth, 13, 15–39.
How to cite: Rizzo, R. E., Burnham, B., Benitez Cunha, G., and Healy, D.: PyFracTend: an Accessible Tool for 3D Stress-State Visualisation and Fault/Fracture Stability Assessment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19338, https://doi.org/10.5194/egusphere-egu26-19338, 2026.
