Benoit Cordonnier

• Vishnu, A. R.; Doan, Mai‐Linh; Hollingsworth, James; Barras, Fabian; Cordonnier, Benoit & Renard, Francois (2026). Shear Fault Formation in Granite Under High and Transient Co‐Seismic Strain Rates Unveiled by Ultra‐Fast X‐Ray Imaging. Geophysical Research Letters. ISSN 0094-8276. 53(14). doi: 10.1029/2025gl120857. Full text in Research Archive Show summary

  During an earthquake a dynamic rupture propagates, causing fractures and permanent damage that modify the mechanical properties of the fault and its surroundings. Reciprocally, the energy dissipated by the mechanical transformation of the fault rock has a direct feedback on the dynamics of the seismic rupture. We reproduce and image these co‐seismic damage processes with sub‐microsecond time resolution through dynamic loading experiments on confined Westerly granite samples. Using synchrotron X‐ray imaging and ultra‐high‐speed cameras, we observed that dynamic compression with confinement produces shear faults and a localized granulation of the rock, known as gouge, before significant slip occurs. This fragmentation process begins with volumetric damage, followed by shear deformation less than 5 microseconds later. Our results indicate that gouge formation is initiated by the dynamic rupture itself, which reduces the strength of a fault prior to other weakening mechanisms that may occur during the earthquake slip.

• Beck, Jessica Ann Mc; Cordonnier, Benoit & Renard, Francois (2026). Asperity dynamics and secondary damage development during the closure of a fracture in granite. Tectonophysics. ISSN 0040-1951. 921. doi: 10.1016/j.tecto.2025.231044. Full text in Research Archive
• Mirzaei, Fazel; Jaiswal, Mukul; Zeman, Jessica Ann; Tekseth, Kim Robert Bjørk; Cordonnier, Benoit & Agofack, Nicolaine [Show all 10 contributors for this article] (2026). Time-Resolved X-ray and Neutron Imaging of Brine Percolation and Liquefaction in an Ultra-Soft Sandstone. Transport in Porous Media. ISSN 0169-3913. 153(3), p. 1–19. doi: 10.1007/s11242-025-02284-z. Full text in Research Archive Show summary

  The inherent instability and risk of liquefaction associated with unstable glaciomarine clay are both scientifically intriguing and societally important. Stabilizing sensitive soils is increasingly necessary with the unfolding climate crisis, which leads to wilder and wetter weather. The relevant length scales extend from nanometer-sized pores to kilometer-sized geological features. Laboratory experiments are important for gaining a better understanding of these phenomena. Here, we present a study of the ultra-soft sandstone Saltwash South, which essentially consists of quartz particles glued together by clay, as a proxy for nanoscopically fine-grained sensitive soil to facilitate time-resolved imaging of the onset of activation and liquefaction. By employing in situ time-resolved combined X-ray and neutron computed tomography (CT), we visualize the structural deformation caused by the presence of water and salts. While neutron imaging was sensitive to the presence of normal and heavy water, simultaneous X-ray imaging was used to measure the porous structure, swelling, and initial liquefaction response of the consolidated rock. Uniform expansion was observed in regions exposed to water, reflecting clay swelling and disaggregation. In tightly confined samples, the swelling and disaggregation were suppressed. Finally, we discuss future perspectives of this promising approach to studying liquefaction phenomena in porous media.

• Beck, Jessica Ann Mc; Cordonnier, Benoit; Zhu, Wenlu & Renard, Francois (2026). Transition From Fracture Propagation to Coalescence in Westerly Granite During the Preparation Process of Macroscopic Failure. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 131(1). doi: 10.1029/2025JB032676. Full text in Research Archive
• Jacob, Jean-Baptiste; Cordonnier, Benoit; Zhu, Wenlu; Vishnu, A. R.; Wright, Jonathan & Renard, Francois (2025). Tracking Intragranular Stress Evolution in Deforming Sandstone Using X-Rays. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 130(7). doi: 10.1029/2025JB031614. Full text in Research Archive
• Shafabakhsh, Paiman; Cordonnier, Benoit; Borgne, Tanguy Le; Mathiesen, Joachim; Linga, Gaute & Pluymakers, Anne [Show all 9 contributors for this article] (2025). Coupling Neutron and X‐Ray Imaging of Fluid Mixing and Precipitation in Rocks: Challenges and Opportunities. Water Resources Research. ISSN 0043-1397. 61(12). doi: 10.1029/2025wr041911. Full text in Research Archive Show summary

  Solute mixing in rocks plays a central role in a wide range of reactive processes. However, how the complex 3D pore structure of rocks governs mixing rates remains largely unknown. Moreover, some mixing‐driven reactions—such as dissolution and precipitation—can modify the pore space, with poorly understood consequences for mixing itself. Recent advances in X‐ray imaging techniques have significantly enhanced our ability to visualize the pore‐scale rock architecture of rocks and a wide range of fluid processes. However, capturing solute mixing and its impact on chemical reactions—such as mineralization—remains a major challenge. Here, we investigated the potential of coupling time‐lapse 3D neutron and X‐ray imaging to characterize reactive fluid mixing and subsequent calcium carbonate mineralization in porous basalt. Two flow‐through experiments were performed with co‐injected CaCl 2 and Na 2 CO 3 , leading to precipitation. Neutron imaging tracked fluid mixing, while X‐ray imaging distinguished the solid matrix from pore space for fluid analysis. The first experiment showed steady transverse mixing, while a second experiment revealed temporal fluctuations due to trapped air, causing multiphase flow. Neutron images indicated significant fluid mixing driven by these fluctuations. A synchrotron X‐ray image post‐experiment indicated additional mineral precipitates from long‐term diffusive mixing. Despite the promising results, several challenges remain, including resolution limits, temporal synchronization between modalities, and accurate fluid phase segmentation. Overall, our findings highlight both the potential and limitations of integrated neutron and X‐ray imaging for studying pore‐scale reactive transport and mineralization processes.

• Prastyani, Erina; Cordonnier, Benoit & Renard, Francois (2025). Generation of large transient porosity at the brittle to semi-ductile transition. Earth and Planetary Science Letters. ISSN 0012-821X. doi: 10.1016/j.epsl.2025.119805. Full text in Research Archive Show summary

  Fluid circulation within Earth’s crust is contingent on the presence of connected porosity. Yet, at depths near the brittle to ductile transition regimes, where the base of the seismogenic zone is located, high pressure compacts the rock, reducing porosity and inhibiting fluid circulation. At greater depths, plastic mechanisms during ductile deformation further reduce the likelihood of porosity generation. In this study, we experimentally simulated the brittle to semi-ductile transition in Carrara marble by performing triaxial deformation experiments coupled with time-lapse 3D synchrotron Xray microtomography at five confining pressures, ranging from 5 MPa to 70 MPa at room temperature and tracked the evolution of porosity over time. Contrary to the prevailing belief, our results show that porosity increases with increasing axial stress at stresses corresponding to the brittle to semi-ductile transition, where fluid circulation is thought to be impeded. In both the semi-brittle and semi-ductile regimes, porosity exhibits similar values, close to 18%, at equivalent axial strain. Although the porosity is comparable, the dominant deformation mechanisms differ: localized shear zones and distributed microcracking characterize the semi-brittle regime, whereas distributed microcracking, without localization, becomes more prominent in the semi-ductile regime. Our findings reveal the formation of high porosity within the semi-brittle and semi-ductile regimes and offer new insight into how this porosity, interpreted as transient within the crust, may enable fluid circulation at the base of the seismogenic zone in Earth's crust.

• Prastyani, Erina; Cordonnier, Benoit; Beck, Jessica Ann Mc; Weiss, Jérôme & Renard, Francois (2025). Mixed-mode deformation in a rock bridge between two fault segments. Tectonophysics. ISSN 0040-1951. 897. doi: 10.1016/j.tecto.2025.230624. Full text in Research Archive Show summary

  Analyzing how fracture networks develop from preexisting isolated fault segments in immature faults may provide knowledge of the preparation process leading to fault growth and dynamic rupture. We reproduce this process experimentally using triaxial compression experiments coupled with time-lapse in-situ synchrotron X-ray tomography in Westerly granite core samples (10 mm diameter, 20 mm height) that contain two parallel notches oriented at 30° with respect to the axis of the cylinder. We conducted the experiments at room temperature with a constant confining pressure of 20 MPa. We image microfracture development, characterize the microphysical processes of damage and fault growth in an intact rock bridge between the notches, and analyze the evolution of fractures oriented at 0°–17° (extensile) and 17°–32° (shear) as the rock approached failure. We also elucidate the strain localization process in the deforming rock using digital volume correlation. Our study offers a detailed comparison of microfracture and strain field development during fault growth. Results indicate that the rock bridge between the notches becomes damaged with a damage rate and a fracture rate diverging as the rock approaches macroscopic failure. Immediately preceding failure, shear fractures dominate the fracture networks. DVC analysis showed that the deformation process is mixed-mode, accommodated by dilation and shear strain, with the shear strains being more localized than the dilation. Furthermore, regions of high dilative strain host both extensile and shear fractures. These findings provide valuable insights into the fault growth process within an intact rock bridge between two fault segments in nature, demonstrating how mixed-mode deformation facilitates fault maturation.

• Mathiesen, Joachim; Beck, Jessica Ann Mc; Cordonnier, Benoit; Ben-Zion, Yehuda & Renard, Francois (2024). Deep‐learning analysis of fracture networks leading to system‐size failure in rocks. Journal of Geophysical Research (JGR): Machine Learning and Computation. 1(3). doi: 10.1029/2023JH000103. Full text in Research Archive Show summary

  Fracture networks in rocks and other geomaterials form by seismic and aseismic damage processes that could lead to system-size failure. Here, we use a multi-view convolutional neural network model to predict the stress proximity to macroscopic failure of experimentally deformed rock samples using two-dimensional images. Models are trained on time series of fractures observed in rock samples through dynamic in situ synchrotron X-ray tomography experiments. The results demonstrate that deep learning models outperform traditional estimates based on fracture density, increasing the accuracy of the predictions. Furthermore, the models provide insights into fundamental characteristics of fracture patterns that may provide precursory information on impending material failure. The trained deep learning models estimate the angle of the fracture plane relative to the principal loading direction, which is a key factor contributing to shear failure. The predicted angle of the fracture plane, in the range of 10°–30° with respect to the direction of maximum compressive stress, is consistent with the established failure criteria used in rock mechanics.

• Jacob, Jean-Baptiste Robert; Wright, Jonathan; Cordonnier, Benoit & Renard, Francois (2024). Exploiting Friedel pairs to interpret scanning 3DXRD data from complex geological materials. Journal of Applied Crystallography. ISSN 0021-8898. 57(6), p. 1823–1840. doi: 10.1107/S1600576724009634. Full text in Research Archive Show summary

  The present study introduces a processing strategy for synchrotron scanning 3D X-ray diffraction (s3DXRD) data, aimed at addressing the challenges posed by large, highly deformed, polyphase materials such as crystalline rocks. Leveraging symmetric Bragg reflections known as Friedel pairs, our method enables diffraction events to be precisely located within the sample volume. This method allows for fitting the phase, crystal structure and unit-cell parameters at the intra-grain scale on a voxel grid. The processing workflow incorporates several new modules, designed to (i) efficiently match Friedel pairs in large s3DXRD datasets containing up to 108 diffraction peaks; (ii) assign phases to each pixel or voxel, resolving potential ambiguities arising from overlap in scattering angles between different crystallographic phases; and (iii) fit the crystal orientation and unit cell locally on a point-by-point basis. We demonstrate the effectiveness of our technique on fractured granite samples, highlighting the ability of the method to characterize complex geological materials and show their internal structure and mineral composition. Additionally, we include the characterization of a metal gasket made of a commercial aluminium alloy, which surrounded the granite sample during experiments. The results show the effectiveness of the technique in recovering information about the internal texture and residual strain of materials that have undergone high levels of plastic deformation.

• Shafabakhsh, Paiman; Cordonnier, Benoit; Pluymakers, Anne Marie Henriette; Borgne, Tanguy Le; Mathiesen, Joachim & Linga, Gaute [Show all 9 contributors for this article] (2024). 4D Neutron Imaging of Solute Transport and Fluid Flow in Sandstone Before and After Mineral Precipitation. Water Resources Research. ISSN 0043-1397. 60(3). doi: 10.1029/2023WR036293. Full text in Research Archive Show summary

  In many geological systems, the porosity of rock or soil may evolve during mineral precipitation, a process that controls fluid transport properties. Here, we investigate the use of 4D neutron imaging to image flow and transport in Bentheim sandstone core samples before and after in-situ calcium carbonate precipitation. First, we demonstrate the applicability of neutron imaging to quantify the solute dispersion along the interface between heavy water and a cadmium aqueous solution. Then, we monitor the flow of heavy water within two Bentheim sandstone core samples before and after a step of in-situ mineral precipitation. The precipitation of calcium carbonate is induced by reactive mixing of two solutions containing CaCl2 and Na2CO3, either by injecting these two fluids one after each other (sequential experiment) or by injecting them in parallel (co-flow experiment). We use the contrast in neutron attenuation from time-resolved tomograms to derive three-dimensional fluid velocity field by using an inversion technique based on the advection-dispersion equation. Results show mineral precipitation induces a wider distribution of local flow velocities and leads to alterations in the main flow pathways. The flow distribution appears to be independent of the initial distribution in the sequential experiment, while in the co-flow experiment, we observed that higher initial local fluid velocities tended to increase slightly following precipitation. The outcome of this study contributes to progressing the knowledge in the domain of reactive solute and contaminant transport in the subsurface using the promising technique of neutron imaging.

• McBeck, Jessica Ann; Cordonnier, Benoit; Ben-Zion, Yehuda & Renard, Francois (2024). Identifying the fracture characteristics that control deformation localization and catastrophic failure in fluid-saturated crystalline rocks in upper crustal conditions. Tectonophysics. ISSN 0040-1951. 871. doi: 10.1016/j.tecto.2023.230191. Full text in Research Archive
• Madathiparambil, Aldritt Scaria; Mirzaei, Fazel; Tekseth, Kim Robert Bjørk; Cordonnier, Benoit; Agofack, Nicolaine & Cerasi, Pierre [Show all 9 contributors for this article] (2024). Mechanical response of cement and shale admixtures under cyclic triaxial loading monitored by in-situ synchrotron micro-computed tomography. Cement and Concrete Research. ISSN 0008-8846. 186. doi: 10.1016/j.cemconres.2024.107682. Full text in Research Archive Show summary

  Understanding the mechanical behaviour of natural soils as mixed with cement for stabilization is crucial for civil engineering developments. The response of cement-soil admixtures when subjected to cyclic loads is a largely unexplored topic, despite the importance of understanding fatigue in these ubiquitous construction materials. We present cyclic loading experiments on Portland cement mixed with fragmented shale fragments using triaxial testing, monitored with synchrotron-based μCT. Through digital volume correlation (DVC), the temporal evolution of the displacement, volumetric, and von Mises equivalent strain fields were obtained. We observed in detail the fatigue damage evolution during cyclic loading and found that following high-strain deformation of the much softer shale fragments, the ultimate failure of the samples occurred in the adjacent cement matrix. The failure mechanism under periodic stress and its relevance for accelerated laboratory testing of slow degradation long-term processes are of key importance to technical infrastructure, including subsea CO2 storage.

• Beck, Jessica Ann Mc; Cordonnier, Benoit; Zhu, Wenlu & Renard, Francois (2024). Spatial Persistence of High Strain Events During Brittle Failure. Geophysical Research Letters. ISSN 0094-8276. 51(21). doi: 10.1029/2024GL110668. Full text in Research Archive Show summary

  The onset of brittle failure in rocks includes dilatancy and strain localization. To better understand this nucleation process, we analyze the evolution of the local three-dimensional strain tensor using X-ray tomograms acquired during triaxial compression experiments on granite and sandstone. The onset of the localization of the compaction, dilation, and shear strain occurs when ∼65% of the rock volume experiences dilation. Tracking the locations of the high strains throughout loading suggests that the deformation that occurs early in loading influences the location of the system-sized fracture network that produces macroscopic failure. This influence is larger in the sandstone experiments than the granite experiments, likely due to the microstructure of the sandstone. These results have important implications for detecting precursors to catastrophic failure.

• McBeck, Jessica Ann; Cordonnier, Benoit; Ben-Zion, Yehuda & Renard, Francois (2023). The Influence of Confining Pressure and Preexisting Damage on Strain Localization in Fluid-Saturated Crystalline Rocks in the Upper Crust. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 128(8). doi: 10.1029/2023JB026987. Full text in Research Archive Show summary

  The spatial organization of deformation may provide key information about the timing of catastrophic failure in the brittle regime. In an ideal homogenous system, deformation may continually localize toward macroscopic failure, and so increasing localization unambiguously signals approaching failure. However, recent analyses demonstrate that deformation, including low-magnitude seismicity, and fractures and strain in triaxial compression experiments, experience temporary phases of delocalization superposed on an overall trend of localization toward large failure events. To constrain the conditions that promote delocalization, we perform a series of X-ray tomography experiments at varying confining pressures (5–20 MPa) and fluid pressures (0–10 MPa) on Westerly granite cores with varying amounts of preexisting damage. We track the spatial distribution of the strain events with the highest magnitudes of the population within a given time step. The results show that larger confining pressure promotes more dilation, and promotes greater localization of the high strain events approaching macroscopic failure. In contrast, greater amounts of preexisting damage promote delocalization. Importantly, the dilative strain experiences more systematic localization than the shear strain, and so may provide more reliable information about the timing of catastrophic failure than the shear strain.

• Madathiparambil, Aldritt Scaria; Tekseth, Kim Robert Bjørk; Mürer, Fredrik Kristoffer; Cordonnier, Benoit; Agofack, Nicolaine & McBeck, Jessica Ann [Show all 10 contributors for this article] (2023). Time-Resolved in Situ Imaging of Strain Localization in Draupne Shale under Triaxial Compression. Physical Review Applied. 20(3). doi: 10.1103/PhysRevApplied.20.034046. Full text in Research Archive
• McBeck, Jessica Ann; Cordonnier, Benoit; Cooke, Michele; Fattaruso, Laura & Renard, Francois (2023). Deformation evolves from shear to extensile in rocks due to energy optimization. Communications Earth & Environment. 4. doi: 10.1038/s43247-023-01023-w. Full text in Research Archive Show summary

  Abstract Determining how fracture network development leads to macroscopic failure in heterogeneous materials may help estimate the timing of failure in rocks in the upper crust as well as in engineered structures. The proportion of extensile and shear deformation produced by fracture development indicates the appropriate failure criteria to apply, and thus is a key constraint in such an effort. Here, we measure the volume proportion of extensile and shear fractures using the orientation of the fractures that develop in triaxial compression experiments in which fractures are identified using dynamic in situ synchrotron X-ray imaging. The fracture orientations transition from shear to extensile approaching macroscopic, system-size failure. Numerical models suggest that this transition occurs because the fracture networks evolve in order to optimize the total mechanical efficiency of the system. Our results provide a physical interpretation of the empirical internal friction coefficient in rocks.

• McBeck, Jessica Ann; Cordonnier, Benoit & Renard, Francois (2023). The evolving representative elementary volume size in crystalline and granular rocks under triaxial compression approaching macroscopic failure. Geophysical Journal International. ISSN 0956-540X. 232(3), p. 1898–1913. doi: 10.1093/gji/ggac426. Full text in Research Archive
• Stappen, Van F. Van; McBeck, Jessica Ann; Cordonnier, Benoit; Pijnenburg, R.P.J.; Renard, Francois & Spiers, C.J. [Show all 7 contributors for this article] (2022). 4D Synchrotron X-ray Imaging of Grain Scale Deformation Mechanisms in a Seismogenic Gas Reservoir Sandstone During Axial Compaction. Rock Mechanics and Rock Engineering. ISSN 0723-2632. 55(8), p. 4697–4715. doi: 10.1007/s00603-022-02842-7. Full text in Research Archive Show summary

  Abstract Understanding the grain-scale processes leading to reservoir compaction during hydrocarbons production is crucial for enabling physics-based predictions of induced surface subsidence and seismicity hazards. However, typical laboratory experiments only allow for pre- and post-experimental microstructural investigation of deformation mechanisms. Using high-resolution time-lapse X-ray micro-tomography imaging (4D µCT) during triaxial deformation, the controlling grain-scale processes can be visualized through time and space at realistic subsurface conditions. We deformed a sample of Slochteren sandstone, the reservoir rock from the seismogenic Groningen gas field in the Netherlands. The sample was deformed beyond its yield point (axial strain > 15%) in triaxial compression at reservoir P–T-stress conditions (100 °C, 10 MPa pore pressure, 40 MPa effective confining pressure). A total of 50 three-dimensional µCT scans were obtained during deformation, at a spatial resolution of 6.5 µm. Time lapse imaging plus digital volume correlation (DVC) enabled identification of the grain-scale deformation mechanisms operating throughout the experiment, for the first time, both at small, reservoir-relevant strains (< 1%), and in the approach to brittle failure at strains > 10%. During small-strain deformation, the sample showed compaction through grain rearrangement accommodated by inter-granular slip and normal displacements across grain boundaries, in particular, by closure of open grain boundaries or compaction of inter-granular clay films. At intermediate and large strains (> 4%), grain fracturing and pore collapse were observed, leading to sample-scale brittle failure. These observations provide key input for developing microphysical models describing compaction of the Groningen and other producing (gas) reservoirs.

• McBeck, Jessica Ann; Aiken, John; Cordonnier, B.; Ben-Zion, Yehuda & Renard, Francois (2021). Predicting Fracture Network Development in Crystalline Rocks. Pure and Applied Geophysics (PAGEOPH). ISSN 0033-4553. 179, p. 275–299. doi: 10.1007/s00024-021-02908-7. Full text in Research Archive Show summary

  Abstract The geometric properties of fractures influence whether they propagate, arrest, or coalesce with other fractures. Thus, quantifying the relationship between fracture network characteristics may help predict fracture network development, and perhaps precursors to catastrophic failure. To constrain the relationship and predictability of fracture characteristics, we deform eight one centimeter tall rock cores under triaxial compression while acquiring in situ X-ray tomograms. The tomograms reveal precise measurements of the fracture network characteristics above the spatial resolution of 6.5 µm. We develop machine learning models to predict the value of each characteristic using the other characteristics, and excluding the macroscopic stress or strain imposed on the rock. The models predict fracture development more accurately in the experiments performed on granite and monzonite, than the experiments on marble. Fracture network development may be more predictable in these igneous rocks because their microstructure is more mechanically homogeneous than the marble, producing more systematic fracture development that is not strongly impeded by grain contacts and cleavage planes. The varying performance of the models suggest that fracture volume, length, and aperture are the most predictable of the characteristics, while fracture orientation is the least predictable. Orientation does not correlate with length, as suggested by the idea that the orientation evolves with increasing differential stress and thus fracture length. This difference between the observed and expected relationship between orientation and length highlights the influence of mechanical heterogeneities and local stress perturbations on fracture growth as fractures propagate, link, and coalesce.

• Kandula, Neelima; McBeck, Jessica Ann; Cordonnier, Benoît; Weiss, Jérôme; Dysthe, Dag Kristian & Renard, François (2021). Synchrotron 4D X-Ray Imaging Reveals Strain Localization at the Onset of System-Size Failure in Porous Reservoir Rocks. Pure and Applied Geophysics (PAGEOPH). ISSN 0033-4553. 179, p. 325–350. doi: 10.1007/s00024-021-02902-z. Full text in Research Archive Show summary

  Abstract Understanding the mechanisms of strain localization leading to brittle failure in reservoir rocks can shed light on geomechanical processes such as porosity and permeability evolution during rock deformation, induced seismicity, fracturing, and subsidence in geological reservoirs. We perform triaxial compression tests on three types of porous reservoir rocks to reveal the local deformation mechanisms that control system-size failure. We deformed cylindrical samples of Adamswiller sandstone (23% porosity), Bentheim sandstone (23% porosity), and Anstrude limestone (20% porosity), using an X-ray transparent triaxial deformation apparatus. This apparatus enables the acquisition of three-dimensional synchrotron X-ray images, under in situ stress conditions. Analysis of the tomograms provide 3D distributions of the microfractures and dilatant pores from which we calculated the evolving macroporosity. Digital volume correlation analysis reveals the dominant strain localization mechanisms by providing the incremental strain components of pairs of tomograms. In the three rock types, damage localized as a single shear band or by the formation of conjugate bands at failure. The porosity evolution closely matches the evolution of the incremental strain components of dilation, contraction, and shear. With increasing confinement, the dominant strain in the sandstones shifts from dilative strain (Bentheim sandstone) to contractive strain (Adamswiller sandstone). Our study also links the formation of compactive shear bands with porosity variations in Anstrude limestone, which is characterized by a complex pore geometry. Scanning electron microscopy images indicate that the microscale mechanisms guiding strain localization are pore collapse and grain crushing in sandstones, and pore collapse, pore-emanated fractures and cataclasis in limestones. Our dynamic X-ray microtomography data brings unique insights on the correlation between the evolutions of rock microstructure, porosity evolution, and macroscopic strain during the approach to brittle failure in reservoir rocks.

• McBeck, Jessica Ann; Cordonnier, B. & Renard, F. (2021). The influence of spatial resolution and noise on fracture network properties calculated from X-ray microtomography data. International Journal of Rock Mechanics And Mining Sciences. ISSN 1365-1609. 147. doi: 10.1016/j.ijrmms.2021.104922. Full text in Research Archive Show summary

  Rock deformation experiments performed at X-ray synchrotrons provide unique insights into the nature of fracture network development. However, these insights depend on the limitations of the X-ray tomography data. Here, we examine how spatial resolution and noise influence the calculated fracture network properties. To assess the influence of spatial resolution, we acquire two overlapping X-ray tomograms with spatial resolution that differ by an order of magnitude. To assess the influence of noise, we produce sets of synthetic tomograms with varying degrees of noise, including point-source noise and blurring noise. In the absence of noise, the differing spatial resolutions produce calculated porosities that differ by 0.05%, or 30% of the porosity measured in the high-resolution data. The fracture property that changes the most in the datasets of varying resolution is the fracture surface area, rather than the volume, length, or aperture. The two types of noise influence the porosity and fracture characteristics in opposite ways. In the synthetic tomograms in which higher values indicate fractures, added point noise increases the porosity while blurring noise decreases the porosity. In volumes with a mapping of gray values in which fractures have lower values, this trend would be reversed. This study is the first to quantify differences in fracture network properties extracted from X-ray tomograms due to spatial resolution and noise.

• Renard, Francois; Kandula, Neelima; McBeck, Jessica Ann & Cordonnier, Benoit (2020). Creep Burst Coincident With Faulting in Marble Observed in 4-D Synchrotron X-Ray Imaging Triaxial Compression Experiments. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 125. doi: 10.1029/2020JB020354. Full text in Research Archive Show summary

  Faults in carbonate rocks show both seismic and aseismic deformation processes, leading to a wide range of slip velocities. We deformed two centimeter‐scale cores of Carrara marble at 25°C and imaged the nucleation and growth of faults using dynamic synchrotron X‐ray microtomography. The first sample experienced a constant confinement of 30 MPa and no pore fluid. The second sample experienced confinement in the range 35–23 MPa and water as a pore fluid at 10 MPa pore pressure. We increased the axial stress by steps until creep deformation occurred and imaged deformation in 4‐D. The samples deformed with a quasi‐constant or increasing strain rate when the differential stress was constant, a process called creep. However, for both samples, we also observed transient events that include the acceleration of creep, that is, creep bursts, phenomena similar to slow slip events that occur in continental active faults. During these transient creep events, strain rates increase and correlate in time with strain localization and the slow development of system‐spanning fault networks. In both samples, the acceleration of opening and shearing of microfractures accommodated creep bursts. High‐resolution time‐lapse X‐ray microtomography imaging and digital image correlation during triaxial deformation quantify creep in laboratory faults at subgrain spatial resolution. This work demonstrates that transient creep events, that is, creep bursts or slow slip events, correlate with the nucleation and slow growth of faults and not only with slip on preexisting faults.

• Panduro, Elvia Anabela Chavez; Cordonnier, Benoit; Gawel, Kamila; Børve, Ingrid; Iyer, Jaisree & Carroll, Susan [Show all 15 contributors for this article] (2020). Real time 3D observations of Portland Cement Carbonation at CO2 storage conditions. Environmental Science and Technology. ISSN 0013-936X. 54(13), p. 8323–8332. doi: 10.1021/acs.est.0c00578. Full text in Research Archive Show summary

  Depleted oil reservoirs are considered a viable solution to the global challenge of CO2 storage. A key concern is whether the wells can be suitably sealed with cement to hinder the escape of CO2. Under reservoir conditions, CO2 is in its supercritical state, and the high pressures and temperatures involved make real-time microscopic observations of cement degradation experimentally challenging. Here, we present an in situ 3D dynamic X-ray micro computed tomography (μ-CT) study of well cement carbonation at realistic reservoir stress, pore-pressure, and temperature conditions. The high-resolution time-lapse 3D images allow monitoring the progress of reaction fronts in Portland cement, including density changes, sample deformation, and mineral precipitation and dissolution. By switching between flow and nonflow conditions of CO2-saturated water through cement, we were able to delineate regimes dominated by calcium carbonate precipitation and dissolution. For the first time, we demonstrate experimentally the impact of the flow history on CO2 leakage risk for cement plugging. In-situ μ-CT experiments combined with geochemical modeling provide unique insight into the interactions between CO2 and cement, potentially helping in assessing the risks of CO2 storage in geological reservoirs.

• Renard, Francois; McBeck, Jessica Ann & Cordonnier, Benoit (2020). Competition between slow slip and damage on and off faults revealed in 4D synchrotron imaging experiments. Tectonophysics. ISSN 0040-1951. 782-783. doi: 10.1016/j.tecto.2020.228437. Full text in Research Archive Show summary

  In the continental crust, faults may accommodate deformation through aseismic creep, slow slip events, or seismic slips that produce dynamic damage, or a combination of these endmembers. A variety of parameters controls the occurrence of these mechanical behaviors. In a series of laboratory experiments, we image centimeter-scale faults during sliding under in situ conditions. We perform four experiments of slip on centimeter-scale crystalline rock samples prepared with a saw-cut interface at 45° from the direction to the maximum compressive stress and at stress conditions of 2–3 km depth. We image fault slip and off-fault fracture development using 4D synchrotron X-ray microtomography. Three faults have an initial rough interface, and deformation occurs with increasing differential stress by a combination of slow slip events and off-fault damage, until catastrophic failure and the formation of new faults. Conversely, the pre-cut fault with a smooth initial surface deforms mainly by slow slip, develops numerous striations along its slip plane, and no microfractures are detected in the wall rock. Our experiments reproduce aseismic and seismic faulting behavior, and demonstrate that the roughness of the fault plane is one of the parameters that control the transition between these two behaviors. A fault with a rougher interface may tend to develop more off-fault damage and seismic behavior. For the rough fault experiments, the secondary faulting occurs along a network of faults oriented at high angles from the pre-existing saw-cut plane, a behavior similar to several earthquake sequences that occurred along orthogonal faults.

• Katayama, Ikuo; Abe, Natsue; Hatakeyama, Kohei; Akamatsu, Yuya; Okazaki, Keishi & Ulven, Ole Ivar [Show all 12 contributors for this article] (2020). Permeability Profiles Across the Crust-Mantle Sections in the Oman Drilling Project Inferred From Dry and Wet Resistivity Data. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 125(8). doi: 10.1029/2019JB018698. Full text in Research Archive Show summary

  Permeability profiles in the crust‐mantle sequences of the Samail ophiolite were constructed based on onboard measurements of the electrical resistivity of cores recovered during the Oman Drilling Project. For each sample, we measured dry and brine‐saturated resistivity during the description campaign on the drilling vessel Chikyu. Owing to the conductive brine in the pore space, wet resistivity is systematically lower than dry resistivity. The difference between dry and wet resistivity is attributed to the movement of dissolved ions in brine that occupies the pore space. We applied effective medium theory to calculate the volume fraction of pores that contribute to electrical transport. Using an empirical cubic law between transport porosity and permeability, we constructed permeability profiles for the crust‐mantle transition zone and the serpentinized mantle sections in the Samail ophiolite. The results indicate that (1) the gabbro sequence has a markedly lower permeability than the underlying mantle sequence; (2) serpentinized dunites have higher permeability than serpentinized harzburgites; and (3) discrete sample permeability is correlated with ultrasonic velocity, suggesting that the permeability variations predominately reflect crack density and geometry.

• Roberts, Aubrey Jane; Druckenmiller, Patrick; Cordonnier, Benoit; Delsett, Lene Liebe & Hurum, Jørn Harald (2020). A new plesiosaurian from the Jurassic–Cretaceous transitional interval of the Slottsmøya Member (Volgian), with insights into the cranial anatomy of cryptoclidids using computed tomography. PeerJ. doi: 10.7717/peerj.8652. Full text in Research Archive Show summary

  Cryptoclidids are a major clade of plesiosauromorph plesiosaurians best known from the Middle—Late Jurassic, but little is known regarding their turnover into the Early Cretaceous. Of the known cryptoclidid genera, most preserve only a limited amount of cranial material and of these Cryptoclidus eurymerus , displays the most complete, but compressed cranium. Thus, the lack of knowledge of the cranial anatomy of this group may hinder the understanding of phylogenetic interrelationships, which are currently predominantly based on postcranial data. Here we present a nearly complete adult cryptoclidid specimen (PMO 224.248) representing a new genus and species Ophthalmothule cryostea gen et sp. nov., from the latest Jurassic to earliest Cretaceous part of the Slottsmøya Member, of central Spitsbergen. The holotype material preserves a complete cranium, partial mandible, complete and articulated cervical, pectoral and anterior to middle dorsal series, along with the pectoral girdle and anterior humeri. High resolution microcomputed tomography reveals new data on the cranial anatomy of this cryptoclidid, including new internal features of the braincase and palate that are observed in other cryptoclidids. A phylogenetic analysis incorporating new characters reveals a novel tree topology for Cryptoclididae and particularly within the subfamily Colymbosaurinae. These results show that at least two cryptoclidid lineages were present in the Boreal Region during the latest Jurassic at middle to high latitudes.

• Cordonnier, Benoit; Pluymakers, Anne Marie Henriette; Tengattini, Alessandro; Marti, Sina; Kaestner, Anders & Fusseis, Florian [Show all 7 contributors for this article] (2019). Neutron Imaging of Cadmium Sorption and Transport in Porous Rocks. Frontiers in Earth Science. doi: 10.3389/feart.2019.00306. Full text in Research Archive
• McBeck, Jessica Ann; Cordonnier, Benoit; Vinciguerra, Sergio & Renard, Francois (2019). Volumetric and Shear Strain Localization in Mt. Etna Basalt. Geophysical Research Letters. ISSN 0094-8276. 46(5), p. 2425–2433. doi: 10.1029/2018GL081299. Full text in Research Archive Show summary

  To examine the impact of preexisting weaknesses on fracture coalescence during volcanic edifice deformation, we triaxially compressed Mount Etna basalt while acquiring in situ dynamic X‐ray microtomograms and calculated the internal strain tensor fields using image correlation. Contraction localization preceded dilation and shear strain localization into the protofault zone. This onset of strain localization preceded macroscopic yielding and coincided with increases in the magnitude and volume of rock experiencing dilation, and spatial clustering of the strain populations. The exploitation of weaknesses by propagating fractures enabled the dominant shear strain to switch senses as propagating fractures lengthened along 30–60° from σ1. Scanning electron microscopy images reveal pore‐emanated fractures, and fractures linking pores. These experiments provide evidence of internal contraction preceding dilation and shear, consistent with inferences from field and laboratory observations. The transition from contraction to dilation may provide a precursory signal of volcanic flank eruption.

• Huang, Lingcao; Baud, Patrick; Cordonnier, Benoit; Renard, Francois; Liu, Lin & Wong, Teng-fong (2019). Synchrotron X-ray imaging in 4D: Multiscale failure and compaction localization in triaxially compressed porous limestone. Earth and Planetary Science Letters. ISSN 0012-821X. 528. doi: 10.1016/j.epsl.2019.115831. Full text in Research Archive Show summary

  Understanding failure and strain localization in porous rock is of fundamental importance in rock physics. Confined compaction experiments on porous rocks have revealed a broad spectrum of failure modes. Techniques such as acoustic emission location and velocity tomography provide kinematic information on the partitioning of damage and localization of strain. Complementary observations on deformed samples using microscopy and microcomputed tomography (μCT) can also be used to image microscale damage and its distribution. Only by synthesizing such measurements on multiple scales could one infer the multiscale dynamics of compaction localization and similar rock failure phenomena. Located at the European Synchrotron Radiation Facility, the HADES rig allows direct in situ 3D imaging of the whole rock sample as it is triaxially compressed. The μCT data provide an integrated perspective of the spatiotemporal evolution of damage and strain localization on scales ranging from grain to continuum. We conducted an experiment on Leitha limestone (initial porosity of ∼22%) at a confining pressure of 20 MPa. With increasing differential stress, the sample strain hardened and two distinct yield points were identified in the stress-strain curve. The spatiotemporal evolution of local porosity and damage were analyzed at multiple scales. At a mesoscopic scale of 10 voxels (65 μm), the time-lapse μCT images reveal the strain partitioning associated with the first yield point and development of strain localization with the second. The latter development of five discrete compaction bands is the first unambiguous observation of such a bifurcation phenomenon in a porous carbonate rock, with geometric attributes comparable to compactions bands observed in porous sandstones. The μCT data on the voxel-scale elucidate in refined details the nucleation and propagation of discrete compaction bands under quasi-static loading, as well as the micromechanical processes, which in the past could only be inferred from a synthesis of kinematic observations of acoustic emissions activity and post-mortem observations of microstructure and damage.

• Zheng, Xiaojiao; Cordonnier, Benoit; McBeck, Jessica Ann; Boller, Elodie; Jamtveit, Bjørn & Zhu, Wenlu [Show all 7 contributors for this article] (2019). Mixed‐mode strain localization generated by hydration reaction at crustal conditions. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 124(5), p. 4507–4522. doi: 10.1029/2018JB017008. Full text in Research Archive Show summary

  Hydration reactions influence rock density and rheology. For example, volume increases produced in hydration reactions may generate sufficient tensile and shear stress to fracture both the rock undergoing the reaction and the surrounding host rock. We performed in situ dynamic X‐ray synchrotron microtomography experiments to investigate reaction‐induced fracturing. Two experiments on hydration of periclase were performed at 180 or 190 °C, under a confinement of 10 or 80 MPa, a pore fluid pressure of 5 or 75 MPa, and with or without differential stress. The sample assembly consists of a periclase cylinder inserted into a central hole within a serpentinite cylinder. The reaction from periclase to brucite results in a large volume increase (110%), pushing the periclase/brucite against the serpentinite and ultimately breaking it. Using time‐resolved three‐dimensional imaging, we quantify the spatial and temporal distribution of the reaction‐induced fractures. We perform digital volume correlation analysis to obtain the incremental strain tensors throughout the hydration and fracturing process. We use numerical models to assess the distribution of stress within the serpentinite. The digital volume correlation results show mixed‐mode strain localization. The von Mises strain, indicative of shear, increases by a larger percentage than the contractive or dilatative strain components as the reaction‐induced fractures grow. The distribution of von Mises strain follows a power law relationship in the cumulative frequency‐magnitude domain, indicative of long‐range elastic stress interactions during fracturing. This experimental finding sheds insights on the mechanisms of microseismicity measured in areas undergoing active serpentinization.

• Renard, Francois; McBeck, Jessica Ann; Kandula, Neelima; Cordonnier, Benoit; Meakin, Paul & Ben-Zion, Yehuda (2019). Volumetric and shear processes in crystalline rock approaching faulting. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 116(33), p. 16234–16239. doi: 10.1073/pnas.1902994116. Full text in Research Archive Show summary

  Understanding the approach to faulting in continental rocks is critical for identifying processes leading to fracturing in geomaterials and the preparation process of large earthquakes. In situ dynamic X-ray imaging and digital volume correlation analysis of a crystalline rock core, under a constant confining pressure of 25 MPa, are used to elucidate the initiation, growth, and coalescence of microfractures leading to macroscopic failure as the axial compressive stress is increased. Following an initial elastic deformation, microfractures develop in the solid, and with increasing differential stress, the damage pervades the rock volume. The creation of new microfractures is accompanied by propagation, opening, and closing of existing microfractures, leading to the emergence of damage indices that increase as powers of the differential stress when approaching failure. A strong spatial correlation is observed between microscale zones with large positive and negative volumetric strains, microscale zones with shears of opposite senses, and microscale zones with high volumetric and shear strains. These correlations are attributed to microfracture interactions mediated by the heterogeneous stress field. The rock fails macroscopically as the microfractures coalesce and form a geometrically complex 3D volume that spans the rock sample. At the onset of failure, more than 70% of the damage volume is connected in a large fracture cluster that evolves into a fault zone. In the context of crustal faulting dynamics, these results suggest that evolving rock damage around existing locked or future main faults influences the localization process that culminates in large brittle rupture events.

• Renard, Francois; McBeck, Jessica Ann; Cordonnier, Benoit; Zheng, Xiaojiao; Kandula, Neelima & Sanchez, Jesus Rodriguez [Show all 12 contributors for this article] (2019). Dynamic In Situ Three-Dimensional Imaging and Digital Volume Correlation Analysis to Quantify Strain Localization and Fracture Coalescence in Sandstone. Pure and Applied Geophysics (PAGEOPH). ISSN 0033-4553. 176, p. 1083–1115. doi: 10.1007/s00024-018-2003-x. Full text in Research Archive Show summary

  Advances in triaxial compression deformation apparatus design, dynamic X-ray microtomography imaging, data analysis techniques, and digital volume correlation analysis provide unparalleled access to the in situ four-dimensional distribution of developing strain within rocks. To demonstrate the power of these new techniques and acquire detailed information about the micromechanics of damage evolution, deformation, and failure of porous rocks, we deformed 3-cm-scale cylindrical specimens of low-porosity Fontainebleau sandstone in an X-ray-transparent triaxial compression apparatus, and repeatedly recorded three-dimensional tomograms of the specimens as the differential stress was increased until macroscopic failure occurred. Experiments were performed at room temperature with confining pressure in the range of 10–20 MPa. Distinct grayscale subsets, indicative of density, enabled segmentation of the three-dimensional tomograms into intact rock matrix, pore space, and fractures. Digital volume correlation analysis of pairs of tomograms provided time series of three-dimensional incremental strain tensor fields throughout the experiments. After the yield stress was reached, the samples deformed first by dilatant opening and propagation of microfractures, and then by shear sliding via grain rotation and strain localization along faults. For two samples, damage and dilatancy occurred by grain boundary opening and then a sudden collapse of the granular rock framework at failure. For the third sample, a fault nucleated near the yield point and propagated in the sample through the development of transgranular microfractures. The results confirm findings of previous experimental studies on the same rock and provide new detailed quantifications of: (1) the proportion of shear versus dilatant strain in the sample, (2) the amount of dilatancy due to microfracture opening versus pore opening when a fault develops, and (3) the role of grain boundaries and pore walls in pinning microfracture propagation and slowing down the rate of damage accumulation as failure is approached. Our study demonstrates how the combination of high-resolution in situ dynamic X-ray microtomography imaging and digital volume image correlation analysis can be used to provide additional information to unravel brittle failure processes in rocks under stress conditions relevant to the upper crust.

• McBeck, Jessica Ann; Kandula, Neelima; Aiken, John Mark; Cordonnier, Benoit & Renard, Francois (2019). Isolating the factors that govern fracture development in rocks throughout dynamic in situ X-ray tomography experiments. Geophysical Research Letters. ISSN 0094-8276. 46(20), p. 11127–11135. doi: 10.1029/2019GL084613. Full text in Research Archive Show summary

  Centuries of work have highlighted the importance of several characteristics on fracture propagation. However, the relative importance of each characteristic on the likelihood of propagation remains elusive. We rank this importance by performing dynamic X‐ray microtomography experiments that provide unique access to characteristics of evolving fracture networks as rocks are triaxially compressed toward failure. We employed a machine learning technique based on logistic regression analysis to predict whether or not a fracture grows from 14 fracture geometry and network characteristics identified throughout four experiments on crystalline rocks in which thousands of fractures propagated. The characteristics that best predict fracture growth are the length, thickness, volume, and orientation of fractures with respect to the external stress field and the distance to the closest neighboring fracture. Growing fractures tend to be more clustered, shorter, thinner, volumetrically smaller, and dipping closer to 30–60° from the maximum compression direction than closing fractures.

• Kandula, Neelima; Cordonnier, Benoit; Boller, Elodie; Weiss, Jérôme; Dysthe, Dag Kristian & Renard, Francois (2019). Dynamics of microscale precursors during brittle compressive failure in Carrara marble. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 124(6), p. 6121–6139. doi: 10.1029/2019JB017381. Full text in Research Archive Show summary

  Microscale heterogeneities influence failure mechanisms in the crust. To track the microstructural changes in rock samples when loaded until failure, we employed a novel experimental technique that couples dynamic X‐ray microtomography imaging with a triaxial deformation apparatus. We studied the brittle failure of Carrara marble under triaxial compression. Dynamic tomographic data revealed the spatial organization of microfractures and damage increments characterizing the precursory activity toward catastrophic failure. We quantified the emergence of scaling relationships between microstructural parameters, including total damage volume, incremental damage volume, the largest connected microfracture, and the applied differential stress. The total volume of microfractures accumulated from the beginning of the experiment as well as the incremental damage showed power law increase. The growth of the largest connected microfracture was related to differential stress as a power law with divergence at failure. The microfracture volume increments were distributed according to a power law with an upper cutoff that itself spanned the entire volume toward failure. These characteristic features of brittle failure in Carrara marble under compression are in agreement with theoretical models that consider failure as a critical phase transition. We also observed that, very close to failure, several power law relationships broke down, which we interpret to be related to the coalescence of the largest microfractures in a finite size volume. Scaling laws and associated exponents computed from our data are compared with predictions made from theoretical and numerical models. Our results show that precursors of macroscopic brittle failure in Carrara marble follow predictable trends.

• Cordonnier, Benoit; Pluymakers, Anne Marie Henriette; Tengattini, Alessandro; Marti, Sina; Kaestner, Anders & Fusseis, Florian [Show all 7 contributors for this article] (2019). Neutron Imaging of Cadmium Sorption and Transport in Porous Rocks. Frontiers in Earth Science. 7, p. 1–11. doi: 10.3389/feart.2019.00306. Full text in Research Archive Show summary

  Understanding fluid flow in rocks is crucial to quantify many natural processes such as ground water flow and naturally triggered seismicity, as well as engineering questions such as displacement of contaminants, the eligibility of subsurface waste storage, geothermal energy usage, oil and gas recovery and artificially induced seismicity. Two key parameters that control the variability of fluid flow and the movement of dissolved chemical species are (i) the local hydraulic conductivity, and (ii) the local sorption properties of the dissolved chemical species by the solid matrix. These parameters can be constrained through tomography imaging of rock samples subjected to fluid injection under constrained flow rate and pressure. The neutron imaging technique is ideal to explore fluid localization in porous materials due to the high but variable sensitivity of neutrons to the different hydrogen isotopes. However, until recently, this technique was underused in geology because of its large acquisition time. With the improved acquisition times of newly set-up neutron beamlines, it has become easier to study fluid flow. In the current set of experiments, we demonstrate the feasibility of in-situ 2D and 3D time-lapse neutron imaging of fluid and pollutant percolation in rocks, in particular that of cadmium salt. Cadmium is a hazardous compound that is found in many electronic devices, including batteries and is a common contaminant in soil and groundwater. It also exhibits higher contrast in neutron attenuation with respect to heavy water, and is therefore an ideal tracer. Time-lapse 2D radiographies and 3D neutron tomographies of the samples were acquired on two neutron beamlines (ILL, France and SINQ, Switzerland). We performed two sets of experiments, imbibition and injection experiments, where we imaged in-situ flow properties, such as local permeability and interactions between cadmium and the solid rock matrix. Our results indicate that even within these cm-scale porous rocks, cadmium transport follows preferential pathways, and locally interacts within the limestone samples. Our results demonstrate that the use of neutron imaging provides additional insights on subsurface transport of pollutants.

• McBeck, Jessica Ann; Cordonnier, Benoit; Mair, Karen & Renard, Francois (2019). The evolving energy budget of experimental faults within continental crust: Insights from in situ dynamic X-ray microtomography. Journal of Structural Geology. ISSN 0191-8141. 123, p. 42–53. doi: 10.1016/j.jsg.2019.03.005. Full text in Research Archive Show summary

  We investigate the evolving distribution of strain produced by a sliding fault within intact crystalline rock, and the energetics of deformation that occur both on- and off-fault. We slid precut faults of differing roughness oriented at 45° to while acquiring in situ X-ray microtomograms. Digital volume correlation of tomograms provide estimates of the 3D displacement and strain fields. This characterization of the strain tensor field reveal that the differing fault roughness produced distinct slip behavior, degree of strain localization and accumulation, and energy budget partitioning. The rougher fault slipped more episodically, hosted a wider and more asymmetric damage zone, and accommodated less normal and shear strain. This fault consumed more energy in off-fault deformation (Wint) per volume and more energy in frictional slip (Wfric) as portions of the total energy input to the system (Wext) than the smoother fault. In both experiments, Wfric consumed the largest portion of the energy budget (50–100%), while Wint consumed smaller percentages (5–20%). Tracking the temporal variability of energy partitioning revealed how evolving fault architecture determined the energetic dominance of particular deformational processes, and so highlighted the importance of tracking energy partitioning through time.

• Renard, Francois; Weiss, Jérôme; Mathiesen, Joachim; Ben-Zion, Yehuda; Kandula, Neelima & Cordonnier, Benoit (2018). Critical Evolution of Damage Toward System-Size Failure in Crystalline Rock. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 123(2), p. 1969–1986. doi: 10.1002/2017JB014964. Full text in Research Archive Show summary

  Rock failure under shear loading conditions controls earthquake and faulting phenomena. We study the dynamics of microscale damage precursory to shear faulting in a quartz‐monzonite rock representative of crystalline rocks of the continental crust. Using a triaxial rig that is transparent to X‐rays, we image the mechanical evolution of centimeter‐size core samples by in situ synchrotron microtomography with a resolution of 6.5 μm. Time‐lapse three‐dimensional images of the samples inside the rig provide a unique data set of microstructural evolution toward faulting. Above a yield point there is a gradual weakening during which microfractures nucleate and grow until this damage span the whole sample. This leads to shear faults oriented about 30° to the main compressive stress in agreement with Anderson's theory and macroscopic failure. The microfractures can be extracted from the three‐dimensional images, and their dynamics and morphology (i.e., number, volume, orientation, shape, and largest cluster) are quantified as a function of increasing stress toward failure. The experimental data show for the first time that the total volume of microfractures, the rate of damage growth, and the size of the largest microfracture all increase and diverge when approaching faulting. The average flatness of the microfractures (i.e., the ratio between the second and third eigenvalues of their covariance matrix) shows a significant decrease near failure. The precursors to faulting developing in the future faulting zone are controlled by the evolving microfracture population. Their divergent dynamics toward failure is reminiscent of a dynamical critical transition. © 2018 Wiley

• McBeck, Jessica Ann; Kobchenko, Maya; Hall, Stephen; Tudisco, Erika; Cordonnier, Benoit & Meakin, Paul [Show all 7 contributors for this article] (2018). Investigating the Onset of Strain Localization Within Anisotropic Shale Using Digital Volume Correlation of Time-Resolved X-Ray Microtomography Images. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 123(9), p. 7509–7528. doi: 10.1029/2018JB015676. Full text in Research Archive Show summary

  Digital volume correlation analysis of time‐resolved X‐ray microtomography scans acquired during in situ triaxial compression of Green River shale cores provided time series of 3‐D incremental strain fields that elucidated evolving deformation processes by quantifying microscopic strain localization. With these data, we investigated the impact of mechanical anisotropy on microscopic strain localization culminating in macroscopic shear failure. We conducted triaxial compression experiments with the maximum compressive stress, σ1, aligned perpendicular and parallel to lamination planes in order to investigate end‐member stress states that arise within sedimentary basins. When the preexisting laminations were perpendicular to σ1, a lamination‐parallel region with high axial compaction developed within the macroscopically linear deformation phase of the experiment and then thickened with increasing applied differential stress. Scanning electron microscopy images indicate that this axial compaction occurred within a lower density lamination and that more axial compaction occurred within the center of the core than near its sides. Boundary element method simulations suggest that this compacting volume promoted shear fracture development within the upper portion of the shale. When the laminations were parallel to σ1, lamination‐parallel dilation bands formed, thickened, and intensified in dilation. Population densities of the distributions of incremental shear strain, radial dilation, and axial contraction calculated by digital volume correlation analysis enabled quantification of the evolving overall impact of, and interplay between, these various deformation modes.

• Zheng, Xiaojiao; Cordonnier, Benoit; Zhu, Wenlu; Renard, Francois & Jamtveit, Bjørn (2018). Effects of Confinement on Reaction-Induced Fracturing During Hydration of Periclase. Geochemistry Geophysics Geosystems. 19(8), p. 2661–2672. doi: 10.1029/2017GC007322. Full text in Research Archive Show summary

  Hydration of a nominally dry rock can cause expansion of the solid volume, resulting in reaction‐induced fracturing and an associated increase in the porosity and permeability of the rock. We study the effect of confinement on the coupling between stress generation, reaction‐induced fracturing, and porosity evolution during the hydration of periclase (MgO) into brucite (Mg(OH)2). Samples of a microporous MgO ceramic were hydrated at 170–210 °C, 5–80 MPa confining pressure, 6–95 MPa differential stress, and 5–75 MPa pore fluid pressure in a purpose‐designed triaxial load cell. Hydration‐induced changes were recorded in situ by X‐ray microtomographic imaging at 5‐min intervals. Below 30 MPa effective mean stress, the fraction of periclase replaced by brucite is a sigmoidal function of time. After a slow start, the replacement rate picks up with concomitant intense fracturing. The porosity increase resulting from the reaction‐induced fractures is transient (pulse‐like). Following the porosity pulse the rate of replacement declines until the replacement is almost complete. Above 30 MPa, the reaction rate is slow, porosity decreases monotonically without any observable fracturing during the time of the experiment. At these stress conditions, the lack of fracturing cannot be limited by the thermodynamic affinity of the reaction. A possible interpretation is that the stress generated by the reaction may overcome the disjoining pressure at the grain‐grain interface, expelling the water film trapped there and thereby dramatically reducing the reaction rate.

• Dunkel, Kristina G; Austrheim, Håkon Olav; Renard, Francois; Cordonnier, Benoit & Jamtveit, Bjørn (2017). Localized slip controlled by dehydration embrittlement of partly serpentinized dunites, Leka Ophiolite Complex, Norway. Earth and Planetary Science Letters. ISSN 0012-821X. 463, p. 277–285. doi: 10.1016/j.epsl.2017.01.047. Full text in Research Archive Show summary

  Dehydration of partly or completely serpentinized ultramafic rocks can increase the pore fluid pressure and induce brittle failure, a process referred to as dehydration embrittlement. However the extents of strain localization and unstable frictional sliding during deserpentinization are still under debate. In the layered ultramafic sections of the Leka Ophiolite Complex in the Central Norwegian Caledonides, prograde metamorphism of serpentinite veins led to local fluid production and to the growth of Mg-rich and coarse-grained olivine with abundant magnetite inclusions and δ18O values ‰ below the host rock. Embrittlement associated with the dehydration caused faulting along highly localized (<10 μm-wide) slip planes near the centers of the original serpentinite veins and pulverization of wall rock olivine. These features along with an earthquake-like size distribution of fault offsets suggest unstable frictional sliding rather than slower creep. Structural heterogeneities in the form of serpentinite veins clearly have first-order controls on strain localization and frictional sliding during dehydration. As most of the oceanic lithosphere is incompletely serpentinized, heterogeneities represented by a non-uniform distribution of serpentinite are common and may increase the likelihood that dehydration embrittlement triggers earthquakes.

• Renard, Francois; Cordonnier, Benoit; Kobchenko, Maya; Kandula, Neelima; Weiss, Jérôme & Zhu, Wenlu (2017). Microscale characterization of rupture nucleation unravels precursors to faulting in rocks. Earth and Planetary Science Letters. ISSN 0012-821X. 476, p. 69–78. doi: 10.1016/j.epsl.2017.08.002. Full text in Research Archive Show summary

  Precursory signals, manifestations of microscale damage that precedes dynamic faulting, are key to earthquake forecasting and risk mitigation. Detections of precursors have primarily relied on measurements performed using sensors installed at some distance away from the rupture area in both field and laboratory experiments. Direct observations of continuous microscale damage accumulated during fault nucleation and propagation are scarce. Using an X-ray transparent triaxial deformation apparatus, we show the first quantitative high resolution three-dimensional (3D) information about damage evolution of rocks undergoing brittle failure. The dynamic microtomography images documented a spectrum of damage characteristics and different fault growth patterns. The interplay between various deformation mechanisms can result in either a positive, negative, or constant net volume change. Consequently, changes in rock density and acoustic wave velocities before faulting are expected to vary in different tectonics settings, hence making failure forecasting intrinsically dependent on rock type at depth.

• Castro, Jonathan M.; Cordonnier, Benoit; Schipper, C Ian; Tuffen, Hugh; Baumann, Tobias & Feisel, Yves (2016). Rapid laccolith intrusion driven by explosive volcanic eruption. Nature Communications. 7. doi: 10.1038/ncomms13585. Full text in Research Archive
• Renard, Francois Marie Paul L; Cordonnier, Benoit; Dysthe, Dag Kristian; Boller, Elodie; Tafforeau, Paul & Rack, Alexander (2016). A deformation rig for synchrotron microtomography studies of geomaterials under conditions down to 10 km depth in the Earth. Journal of Synchrotron Radiation. ISSN 0909-0495. 23(4), p. 1030–1034. doi: 10.1107/S1600577516008730. Full text in Research Archive

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• Zeman, Jessica Ann; Cordonnier, Benoit; Luani, Giacomo; Mathew, Arshitha; Pallipotta, Soumya & Panduro, Elvia Anabela Chavez [Show all 8 contributors for this article] (2025). Investigation of Fluid Dynamics in CO2 Storage Using Computed Tomography. Full text in Research Archive
• Madathiparambil, Aldritt Scaria; Mürer, Fredrik Kristoffer; Tekseth, Kim Robert Bjørk; Agofack, Nicolaine; Cerasi, Pierre & Cordonnier, Benoit [Show all 10 contributors for this article] (2021). In situ computed tomography studies of strain evolution in Draupne shales. Full text in Research Archive
• Sanchez, Jesus Rodriguez; Cordonnier, Benoit; Renard, Francois & Dysthe, Dag Kristian (2016). Transition between brittle and ductile behaviour on carbonate rocks: an X-ray tomographic analysis. Full text in Research Archive
• Prastyani, Erina; Renard, Francois; Cordonnier, Benoit & McBeck, Jess (2026). 4D Imaging of Brittle to Semi-ductile Deformation in Crystalline Rock. Universitetet i Oslo. Full text in Research Archive Show summary

  This thesis investigates the fundamental links between strain localization, porosity evolution, and deformation mechanisms across the brittle-to-semi-ductile transition in crystalline rock. Using a multidisciplinary approach that combines triaxial deformation experiments with in-situ 4D X-ray microtomography and acoustic emission monitoring, this work quantifies the seismic and aseismic processes governing deformation. In the brittle regime, this work elucidates how strain partitioning between dilation and shear drives fault growth within intact rock bridges. As deformation reaches the semi-ductile regime, this research captures the evolution of substantial transient porosity and pore connectivity, quantifying the volumetric strain partitioning that might influence fault stability and fluid transport in the middle crust. By challenging the view of the brittle-ductile transition as a static, low-porosity barrier, this thesis provides a dynamic framework for understanding the occurrence of slow slip events, aseismic creep, and deep fluid migration near the base of the seismogenic zone.

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