EMRP1.16
Open session in Rock Physics

EMRP1.16

EDI
Open session in Rock Physics
Convener: Sergio Vinciguerra | Co-convener: Patrick Baud
Presentations
| Thu, 26 May, 13:20–14:50 (CEST)
 
Room -2.31

Presentations: Thu, 26 May | Room -2.31

Chairperson: Sergio Vinciguerra
13:20–13:21
13:21–13:28
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EGU22-1147
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ECS
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On-site presentation
Ronald Pijnenburg and Richard Wessels and the EPOS-NL team

Top research into the geo-societal challenges of our densely populated planet requires optimized use of available research data, facilities, and funds. Such optimization is the main aim of the European Plate Observing System – Netherlands (EPOS-NL): the Dutch research infrastructure for solid Earth sciences. EPOS-NL provides free of charge, (inter)national access to a unique cluster of large-scale, geophysical labs and data centers at Utrecht University (UU), Delft University of Technology (TU Delft) and the Royal Netherlands Meteorological Institute (KNMI). Lab access can be requested by applying to one of our biannual calls. EPOS-NL labs that can be accessed include A) The Earth Simulation Laboratory at UU and the Petrophysics laboratory at TU Delft, where experimental rock physics and analogue modelling studies can be performed on the fundamental processes that govern the deformation and transport behavior of the Earth’s crust and upper mantle; and B) The Multi-scale Imaging and Tomography (MINT) facilities, distributed over UU and TU Delft. MINT provides unprecedented capabilities in 2D and 3D imaging and microchemical and crystallographic mapping, down to a resolution of several nanometers. EPOS-NL further works with data centers, researchers and industry to improve open access to essential Earth scientific data and models. These include key data relating to the seismogenic Groningen gas field in the Netherlands, notably Distributed Strain Sensing data of the gas reservoir, a Petrel geological reservoir model, developed by the field operator NAM (Nederlandse Aardolie Maatschappij), and a vast amount of seismological data maintained by the ORFEUS Data Centre. Access is provided in the framework of the European infrastructure EPOS, cf. FAIR (Findable, Accessible, Interoperable and Reusable) data principles. In that way, EPOS-NL contributes to shared and cost-effective research into the geo-societal challenges faced by our densely populated planet. See www.EPOS-NL.nl for more information.

How to cite: Pijnenburg, R. and Wessels, R. and the EPOS-NL team: Open access to Dutch Earth scientific research labs and data through EPOS-NL, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1147, https://doi.org/10.5194/egusphere-egu22-1147, 2022.

13:28–13:35
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EGU22-6004
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ECS
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On-site presentation
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Cláudia Cruz, Joana Dias, Eric Font, Fernando Noronha, and Helena Sant'Ovaia

The presence of magnetite in granitoids is usually rare in the Iberia Peninsula, but can occur depending on the crystal fractionation processes and redox conditions. Here we studied the Manteigas granodiorite in order to characterize and quantify the nature and abundance of ferromagnetic minerals by using petrographic, Isothermal Remanent Magnetization (IRM) curves, and Frequency-dependent Susceptibility (KfD%) experiments. Igneous rocks of the Variscan age are particularly abundant in Central Portugal, including the Manteigas granodiorite that crops out in the Serra da Estrela region (Central Iberian Zone), Portugal. The Manteigas granodiorite is classified as a medium- to coarse-grained slightly porphyritic biotite rock and was dated by U-Th-Pb methods on zircon at 481.1 ± 5.9 Ma. Petrographic studies show that Manteigas is mainly composed of quartz, Ca-plagioclase, K-feldspar, and biotite. As accessory minerals, apatite, chlorite, magnetite ± hematite, and zircon are identified. Muscovite is rare and most of secondary origin. Monazite, sphene-leucoxene, and brookite-anatase are also present but in minor amounts. Microstructures indicate a slight deformation that is reflected in the undulatory extinction in quartz, microfractures in K- feldspar, and curved biotites. Sometimes microfractures in feldspar are filled by later Fe-oxide/hydroxide. Values of magnetic susceptibility (Km) indicate that the Manteigas granodiorite belongs to the magnetite-type rocks, with Km values higher than 1.9 x 10-3 SI (1.9 x 10-3 SI < Km < 188.37 x 10-3 SI). This is consistent with oxidizing conditions in the magma genesis [1]. Furthermore, the oxygen isotope composition (δ18O) measured on whole-rock samples ranges between 8.8 ‰ and 8.9 ‰ [1,2], which suggests a mantle contribution. The analysis of IRM data through the Cumulative Log-Gaussian (CLG) function with the software developed by Kruiver et al. [3] indicates the presence of a single ferromagnetic s.l. component, with values of mean coercivity (Log B1/2) of 1.61 mT and dispersion parameter (DP) of 0.36, typical of magnetite [4]. The value of the IRM at saturation (SIRM) of 18 A/m indicates a significant contribution of magnetite. We also fitted the IRM curve by using a Skewed Generalized Gaussian function with the MaxUnmix software [5] and obtained similar results. Kfd% analyses were conducted in four samples. Values of the Kfd% are inferior to 6%, suggesting a very weak contribution of superparamagnetic particles. Acknowledgments: The first author is financially supported by UIDP/04683/2020 project (FCT-Portugal). This work is also supported by national funding awarded by FCT under UIDB/04683/2020 project. References: [1] Sant’Ovaia, H., Olivier, P., Ferreira, N., Noronha, F., Leblanc, D. 2010. J. Struct. Geol. 32, 1450-1465. [2] Neiva, A., Williams, I.S., Ramos, J.M.F., Gomes, M.E.P. Silva, M.M.V.G., Antunes, I.M.H.R. 2019. Lithos 111, 186-202. [3] Kruiver, P.P., Dekkers, M.J., Heslop, D. 2001. Earth Planet. Sci. Lett. 189, 269–276. [4] Egli, R., 2003. J. Geophys. Res. 108, 2081. [5] Maxbauer, D.P., Feinberg, J. M., Fox, D.L. 2016.  Comput. Geosci. 95, 140–145.

How to cite: Cruz, C., Dias, J., Font, E., Noronha, F., and Sant'Ovaia, H.: Disclosing the redox conditions in Central Portugal magmatism: the Manteigas granodiorite case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6004, https://doi.org/10.5194/egusphere-egu22-6004, 2022.

13:35–13:42
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EGU22-6331
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ECS
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Virtual presentation
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António Oliveira, Helena Sant'Ovaia, and Helena Brites

Several hypabyssal dykes and masses, generated during the Permo-Carboniferous, outcrop throughout southwest Europe. In Portugal, this magmatic event is related to the transition from a post-collisional to extensional setting that followed the Variscan orogeny and represented by porphyries, lamprophyres, and dolerites which intruded into older metasediments and granites. The magnetic mineralogy, susceptibility, and fabrics of selected dykes from northern Portugal were studied using methodologies such as IRM curve acquisition and treatment, frequency-dependence of the magnetic susceptibility (Kfd), and low-field AMS.

Based on the bulk magnetic susceptibility, the felsic lithotypes are paramagnetic (Km = 0.9-148.2 µSI) but mostly composed of diamagnetic minerals (i.e., quartz and feldspars). AMS in these rocks is mainly carried by iron-bearing silicates, such as biotite and cordierite, as well as ilmenite. However, other iron oxides, namely hematite, goethite, or fine-grained magnetite, also play an important role in the magnetic anisotropy. By contrast, in most of the mafic lithologies (Km = 238.2-15,640.7 µSI), magnetite is an essential component. Other iron-rich minerals such as biotite, amphibole, and pyroxene also influence the anisotropy of these rocks.

Following the IRM data treatment (Kruiver et al., 2001; Maxbauer et al., 2016), all samples reveal at least one magnetite grain population whose mean coercivities (B1/2) and dispersion parameter (DP) range from 18.2 to 70.8 mT and 0.26 to 0.40, respectively. Petrographic observations suggest that most magnetite composing the mafic rocks is multidomain-type. However, Kfd measurements (4.66-18.18%) indicate that superparamagnetic particles are likely to exist in some lithologies, inducing low bulk susceptibilities and anomalous AMS fabrics. On the other hand, inverse fabrics are probably associated with hydrothermal and/or post-magmatic alterations.

Many felsic specimens display a normal fabric, where the magnetic minerals were oriented along the magma flow direction within the dyke and undisturbed by tectonic strains. Such observation is compatible with the average low anisotropy degree (Ppara% = 0.92-4.28%), implying passive emplacement of the melts, and possibly reflects a weak contribution from single-domain-magnetite. Rare cases where the magnetic fabric is intermediate presumably point to more intense deformations.

Magnetite on the mafic rocks is mainly primary. By contrast, since the felsic dykes derived from anatexis of pelitic sources, their generation occurred under reducing conditions, being similar to Ilmenite-type granites. As such, most magnetite in the felsic samples is probably secondary, having resulted from exsolution from Fe-bearing minerals. However, the presence of primary magnetite cannot be ruled out due to possible magma mixing, as suggested by the coexistence of mantled and non-mantled feldspars. The less evolved member involved in the mixing process is likely to carry a more oxidized composition, bearing the potential to crystallize primary magnetite.

This work was supported by the Portuguese Foundation for Science and Technology (FCT), through the project reference UIDB/UIDP/04683/2020 and ICT (Institute of Earth Sciences). The main author is also financially supported by FCT through an individual Ph.D. grant (reference SFRH/BD/138818/2018). References: Kruiver, P.P., Dekkers, M.J., Heslop, D., 2001. Earth Planet. Sci. Lett. 189, 269–276. Maxbauer, D.P., Feinberg, J. M., Fox, D.L., 2016. Computers & Geosciences 95, 140–145.

How to cite: Oliveira, A., Sant'Ovaia, H., and Brites, H.: Unveiling the magnetic mineralogy and magma flow dynamics within subvolcanic dykes from northern Portugal, Central Iberian Zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6331, https://doi.org/10.5194/egusphere-egu22-6331, 2022.

13:42–13:49
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EGU22-209
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ECS
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On-site presentation
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Nisar Ahmed, Wiktor Waldemar Weibull, and Dario Grana

Seismic amplitude versus offset inversion has gained increased attention over the years and is a pragmatic tool applied to retrieve the seismic and petrophysical properties of the geological layers. The prediction of these petro-elastic properties plays an important role in litho-fluids identification and quantitative seismic reservoir characterization. However, imaging of these subsurface variables from the pre-stack seismic data requires minimizing the objective function and is generally solved by using a gradient-descent based optimization method. This method requires computing the gradients of the cost function with reference to the rock’s variables. We have introduced a model-based non-linear AVO inversion strategy that is based on the computation of the adjoint-state gradients. The forward seismic modelling is carried out by convolving the seismic wavelet with the reflectivity series modelled by using the linearized AVO approximation. The optimization method known as L-BFGS is implemented to attain the best optimal model. The novelty of this work is the adjoint-state solution of the linearized AVO equation. This inversion method has been successfully applied on single and multi-traced seismic data simulated with different seismic noise levels. The modelled examples show that the presented non-linear inversion method accurately extract the seismic properties including seismic (P and S) wave velocities and bulk density. Even at some realistic seismic noise levels, the true and extracted model show good agreement which demonstrates the wide application to solve the AVO inverse modelling problems.

How to cite: Ahmed, N., Weibull, W. W., and Grana, D.: Adjoint-state Method Based Strategy for Non-linear Seismic AVO Inversion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-209, https://doi.org/10.5194/egusphere-egu22-209, 2022.

13:49–13:56
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EGU22-3008
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Virtual presentation
Enes Zengin

Determination of strength and deformation parameters of rocks are crucially important for many engineering structures. In recent decades, numerical modelling and analysis have become a critical part of engineering projects due to significant advances in software technologies and computational infrastructure. As with the dilemmas brought by every new development, differences between 2D and 3D modelling approaches need to be considered. In nature, rocks are exposed to stresses from multi-dimensions. In order to create representative and reliable models to assess the behaviour of rock, this natural phenomenon must have been taken into account. On the other hand, in many studies on rock mechanics and modelling, 2D models are used. The reasons behind this choice can be listed as computational load, time, effort, and the results being in the preferred and reliable range. In addition, it is an inevitable fact that the importance of 3D modelling will increase since developing technologies and engineering structures begin to push the limits of the known engineering experience of engineers. In this study, 2D and 3D models were created by using Particle Flow Code (PFC) for a Castlegate sandstone sample to evaluate the response of 2D and 3D models under similar stress conditions. For this purpose, uniaxial compressive strength, triaxial compressive strength, and tensile strength tests were performed on both intact rock and gapped (circular in 2D and spherical in 3D) models to obtain data from different scenarios. Although both models provide similar test results, 3D models offer much more detail, especially in parameters such as crack initiation, propagation, and stress localization. Here, it can be said that the differences in the behaviours arise from the number of the balls in 3D models, which is more than 3 times in 2D, and the number of contacts which is more than 6 times, respectively. However, because of this resolution, the model response to stress conditions is closer to nature. The computational load for the 3D model is much higher than the 2D model because of the resolution. Even though 3D models have some drawbacks compared to 2D models in terms of computational load, time, and effort, it can be said that the data they provide is much more representative and reliable, especially in terms of model behaviour.

How to cite: Zengin, E.: Representative and Reliable Modeling for Rock Materials: 2D vs 3D, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3008, https://doi.org/10.5194/egusphere-egu22-3008, 2022.

13:56–14:03
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EGU22-12478
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ECS
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Presentation form not yet defined
Exploring new experimental possibilities for the investigation of nonlinear mesoscopic elasticity
(withdrawn)
Manuel Asnar, Audrey Bonnelye, Christoph Sens-Schönfelder, and Georg Dresen
14:03–14:10
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EGU22-3748
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ECS
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On-site presentation
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Federico Pignalberi, Marco Maria Scuderi, Corentin Noël, Chris Marone, and Cristiano Collettini

Tectonic fault zones are subject to normal stress variations with a wide range of spatiotemporal scales, resulting in stress field alteration. These perturbations can spread over a wide range of frequencies and amplitudes from the high frequency passage of seismic waves generated by earthquakes, to the low frequency of solid earth tides and underground fluid injection cycles. As a result of these normal stress perturbations, critically stressed faults can be reactivated. The resulting slip mode is then controlled by fault friction and elastic properties of the surrounding rock. Existing works show that complex behaviors may arise from the interplay between friction changes with slip and slip rate and stress perturbations.

To shed light on the mechanics of fault dynamic triggering we performed experiments in a Biaxial Apparatus in a Double Direct Shear configuration under critically stable stiffness conditions (K/Kc~1). We used powdered quartz gouge (Min-U-Sil 40) as starting material, and conducted experiments at reference normal stress of σn = 10-13.5 MPa. After shearing the material and reaching a steady state sliding, normal stress oscillations were applied with various amplitudes, varying from A = 0.5-2 MPa, and periods, T = 0.5-50 s. In addition, we used the laboratory derived friction parameters as input for forward modeling using Rate-and-State friction laws in order to assess if these laws can explain our data. Our results show that creeping faults, under critical stiffness conditions, are sensitive to normal stress perturbations showing a variety of slip behaviors depending on amplitude and frequency of the oscillations:

  • Oscillation frequency has a major effect on fault stability. Low and high frequencies cause a Coulomb-like response of the shear stress, that is accompanied by a complex frictional response with slow events and period doubling. At the critical frequency predicted by the Rate-and-State friction, we observe dynamic weakening resulting in regular stick-slip events.
  • Oscillation amplitude also plays a role with the main effect depending on the magnitude of the perturbation.
  • Using a modified Rate-and-State equation (Linker and Dieterich, 1992), we are able to accurately model the laboratory data.

Our results show that normal stress perturbation on a laboratory creeping fault, at critical stiffness condition, can reproduce the entire spectrum of fault slip behavior depending on the oscillation properties.

How to cite: Pignalberi, F., Scuderi, M. M., Noël, C., Marone, C., and Collettini, C.: Stress triggering and the spectrum of fault slip behaviors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3748, https://doi.org/10.5194/egusphere-egu22-3748, 2022.

14:10–14:17
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EGU22-5818
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ECS
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Presentation form not yet defined
Micromechanics of damage localisation and shear failure in a porous rock: sound and vision
(withdrawn)
Alexis Cartwright-Taylor, Maria-Daphne Mangriotis, Ian G. Main, Ian B. Butler, Florian Fusseis, Martin Ling, Edward Andò, Andrew Curtis, Andrew F. Bell, Crippen Alyssa, Roberto E. Rizzo, Sina Marti, Derek D. Leung, and Oxana V. Magdysyuk
14:17–14:24
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EGU22-3183
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On-site presentation
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Sergio Vinciguerra, Thomas King, and Philip Benson

Parametric analysis of laboratory Acoustic Emission (AE) during rock deformation laboratory experiments has revealed periodic trends and precursory behaviour of the rupture source, as crack damage nucleates, grows and coalesces into a fault zone. Due to the heterogeneity of rocks and the different effective pressures, finding a full prediction of rupture mechanisms is still an open goal. We consider the AE rates and the derived source mechanisms to constrain the stress-strain regime, while scattering and seismic velocity structure define the evolving medium state as the most important attributes for the neural network model to learn. 4x10cm samples of Alzo granite were deformed at confining pressures of 5-40 MPa, whilst AE are recorded. Source mechanisms, as well as AE rates with relation to incremental strain, highlight distinct pre-failure phases. Scattering and seismic velocity measurements indicate the evolving mechanical conditions. A 10MPa simulation test on a model trained with data from 5, 20 and 40 MPa highlights good accuracy when predicting sample failure.

It remains a challenge to generate a ‘generic’ model that can be applied over all experimental conditions. Nonetheless, estimation of parameter importance has highlighted that some physical parameters are better for predicting strain, whilst others are better at stress. This importance can vary in time, suggesting a strong sensitivity of AE properties to the dynamic conditions of the fault zone. Small input changes can strongly affect output, therefore multiple models need to be trained in order to confirm the stability of the forecast. We aim to improve the understanding of the analysis through the search of repeating trends and the identification of consistent variations in key time-varying trends. Seismic scattering shows an early relevance, interpreted as due to the breakup of low frequency surface waves as microcracks begin to coalesce. However the reduction of importance at the later phases of deformation is less obvious. Further investigations are needed to identify at which deformation stage individual parameters are more important and segment time series accordingly.

How to cite: Vinciguerra, S., King, T., and Benson, P.: Using AE based Machine Learning Approaches to Forecast Rupture during Rock Deformation Laboratory Experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3183, https://doi.org/10.5194/egusphere-egu22-3183, 2022.

14:24–14:31
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EGU22-3813
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ECS
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On-site presentation
Tatiana Kartseva, Nikolai Shapiro, Andrey Patonin, Vladimir Smirnov, and Alexander Ponomarev

We propose a coda-based estimation of source parameters of acoustic events recorded in laboratory experiments on rock deformation. Coda-waves are considered as the reverberation of the acoustic field in the tested sample. After multiple reverberations, the resulting wavefield can be approximated as nearly homogeneously distributed over the sample and with signal amplitudes decaying exponentially in time (linearly in a logarithmic scale). Within the framework of this model, the frequency-dependent coda amplitude at any moment of time is described as combination of a source spectra, of a decay rate combining internal attenuation with reverberation losses, and of a sensor response. One of the main difficulties with the laboratory experiments is that acoustic sensors are very difficult to calibrate and their absolute response function in most of cases remains unknown. With the simple reverberation model, the logarithms of coda amplitudes at different times and sensors and for multiple events are described by a system of linear equations that we solve in a least-square sense to find frequency-dependent decay rates and relative source spectra and sensor responses. In a next step, we compute spectral ratios between different events to eliminate the sensor responses and to estimate main source parameters such as corner frequencies and relative seismic moments. Additionally, we propose a new method for computing relative magnitudes (energy classes) of acoustic emission events from the coda envelopes and argue that it might be more robust comparing with estimations based on first arrivals.

We provide details of our data analyses tehnique and present first results of our new coda-based method applied to 30-600 kHz signals recorded during experiments carried out in the Research Equipment Sharing Center of IPE RAS “Petrophysics, Geomechanics and Paleomagnetism” on a controlled hydraulic press INOVA-1000 of the Geophysical Observatory ”Borok”, IPE RAS with granites of the Voronezh massif and Berea sandstones.

How to cite: Kartseva, T., Shapiro, N., Patonin, A., Smirnov, V., and Ponomarev, A.: Coda-Based Estimation of Source Parameters of Laboratory Acoustic-Emission Events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3813, https://doi.org/10.5194/egusphere-egu22-3813, 2022.

14:31–14:38
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EGU22-5890
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ECS
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On-site presentation
Jon-Danilo Kortram, Auke Barnhoorn, and Anne Pluymakers

Active use of the subsurface alters the in-situ pore-fluid composition. For limestone, chemical interaction between the pore fluid and the rock has been shown to alter some of the mechanical parameters, though the exact nature of this mechano-chemical interaction is not yet fully understood. To address this, we performed tri-axial compressive experiments on two highly pure (>97% CaCO3) and well documented limestones: Indiana Limestone and Edwards White, which were saturated with different fluid compositions. We selected our samples to have a porosity within a narrow range: 23.2 ± 0.3% for Edwards White and 12.9 ± 0.5% for Indiana Limestone. Prior to testing, the rock samples were saturated under vacuum with a fluid solution, and left to equilibrate under vacuum at room temperature for 18 hours. The fluids used in our experiments are 1) CaCO3-saturated water, 2) a brine which has a composition representative for the Dutch subsurface, and 3) a solution of industrial corrosion inhibitor. Samples were tested at room temperature and confining pressures of 2.5, 5 and 10 MPa. In addition to the stress and strain data observed from these experiments, thin sections were made from the deformed samples to perform micro-structural analysis on the damage zone.

Our results show no mechano-chemical effects for Edwards White. However, the rock strength of the Indiana limestone samples changes due to the different pore fluids: At a confining pressure of 2.5 MPa the sample saturated with to CaCO3 solution failed at 49 MPa, compared to 47 MPa and 54 MPa for the samples that were saturated with the brine and the inhibitor solution respectively. At a confining pressure of 5 MPa both the sample tested with the CaCO3 solution and the brine solution failed at 57 MPa and the sample exposed to the inhibitor solution failed at 56 MPa. The samples tested at a confining pressure of 10 MPa respectively failed at: 76, 79 and 73 MPa.  These differences of 5 to 10% lead to a shift in the resulting failure envelopes depending on the pore fluid used in the experiments when describing the failure behaviour of these samples using the Mohr-Coulomb failure criterion: The group tested with CaCO3 solution had a cohesion of 11 MPa and the coefficient of friction of 0.67. For the samples tested with brine solution these values are 10 MPa and 0.71 respectively. For the group tested with inhibitor solution these values equal 15 MPa and 0.47 respectively. The experiments presented here serve as a baseline from which we can further determine which ions or compounds interact with the rock, and the nature of this interaction. For our follow-up work, we will continue by performing a detailed microstructural analysis to better understand the overall controls on the mechano-chemical interactions or the lack thereof. In follow-up experiments, we will narrow down the complexity of the fluid solutions so we can identify the effect of specific ionic species.

How to cite: Kortram, J.-D., Barnhoorn, A., and Pluymakers, A.: The effect of pore fluid chemistry on limestone deformation., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5890, https://doi.org/10.5194/egusphere-egu22-5890, 2022.

14:38–14:48
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EGU22-9866
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ECS
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solicited
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Virtual presentation
Chiara Cornelio, Elena Spagnuolo, Stefan Nielsen, Stefano Aretusini, Francois Passelègue, Marie Violay, Massimo Cocco, and Giulio Di Toro

While sliding at seismic slip-rates of ca. 1 m/s, a natural fault undergoes an abrupt decrease of its strength called enhanced dynamic weakening. Asperity-scale (<< mm) processes related to flash heating & weakening and meso-scale (mm-cm) processes involving shear across the bulk slipping zone related to frictional melting or viscous flow of minerals, have been invoked to explain pronounced velocity-dependent weakening. Here we present a compilation of ca. 100 experiments performed with two rotary shear apparatuses, i.e. SHIVA installed in INGV (Rome, Italy) and HVR installed, at the time of experiments, in Kyoto University (Japan). Cohesive rock cylinders of basalt, gabbro, tonalite, granite and calcitic marble were sheared under a range of effective normal stresses (sn=5-40 MPa), target slip-rates (Vt=0.1-6.5 m/s) and fluid pressures (from room humidity conditions RH or Pf=0, to Pf =15 MPa). We fit the measured shear stress evolution with slip with two dynamic weakening mechanisms models, which include, depending on rock type: (1) flash heating and bulk melting (granitoid, gabbro and basalt), (2) flash heating and diffusion creep (calcitic marble), (3) flash heating and dislocation creep (calcitic marble). We provide a set of optimized parameters, specific for each mechanism, that control the dynamic weakening.

Lastly, the modelling procedure allow us to estimate the slip-switch distance d0, i.e. the slip necessary for the complete transition from the asperity-scale to bulk slipping zone dynamic weakening mechanism. Our analysis shows that (1) the d0 decreases with increasing effective normal stress acting on the fault and, (2) for the same type of transition between dynamic weakening mechanisms (e.g., from flash heating to bulk melt lubrication) the d0 is a function of rock composition. The decrease of d0 with normal stress indicates that during earthquakes, bulk mechanisms dominate over asperity scale weakening mechanisms with increasing crustal depths. This study provides constitutive law parameters to be included in physically- and geologically-based dynamic earthquake rupture simulations.

How to cite: Cornelio, C., Spagnuolo, E., Nielsen, S., Aretusini, S., Passelègue, F., Violay, M., Cocco, M., and Di Toro, G.: Determination of parameters characteristic of dynamic weakening mechanisms during coseismic slip, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9866, https://doi.org/10.5194/egusphere-egu22-9866, 2022.

14:48–14:50