François Renard

• Aspaas, Andreas Grøvan; Bievre, Grégory; Lacroix, Pascal; Langet, Nadege; Aga, Juditha & Skrede, Ingrid [Show all 9 contributors for this article] (2026). Seasonal and inter-annual evolution of the deformation of two Arctic landslides. Earth Surface Dynamics. ISSN 2196-6311. 14(5), p. 729–761. doi: 10.5194/esurf-14-729-2026. Full text in Research Archive Show summary

  Landslides in glacial and periglacial environments are increasingly affected by climate change, with sudden failures reported in high mountain regions and the Arctic. The complex mechanisms behind these events are often poorly understood due to a lack of dense in situ data. We investigate two slow-moving landslides in Arctic Norway (70° N), the Jettan and Gámanjunni landslides, located approximately 10 km apart: Jettan, a complex slide in micaschist and calcite marble situated below the permafrost boundary, and Gámanjunni, a rotational slide in micaschist situated above the permafrost boundary. Using over a decade of multi-physics observations, including geodetic, borehole, seismic, and hydrological data, we examine surface and subsurface deformation. Both landslides display similar seasonal surface velocity patterns, with peaks in spring and autumn, likely influenced by pore-water infiltration. At Jettan, twelve years of inclinometer data in boreholes reveal a transition from steady state to seasonal deformation in two shear zones. Since 2020, spring accelerations have intensified in years coinciding with deeper snowpacks and associated melt. These observations, together with statistical modeling, suggest that the shear-zones are becoming increasingly localized and sensitive to pore-water pressure. Conversely, autumn acceleration is not seen in localized shear zones but manifests as distributed volumetric deformation. Seismic velocity variations within the landslide body also exhibit seasonal patterns that correspond with geodetic velocity, interpreted as changes in landslide rigidity due to water infiltration. This integrated analysis of surface and subsurface data offers new insights into the evolving deformation of Arctic landslides, emphasizing the influence of hydrological forcings on both seasonal and long-term deformation processes.

• Prastyani, Erina; Wang, Lei; McBeck, Jessica; Cordonnier, Benoît; Rybacki, Erik & Dresen, Georg [Show all 7 contributors for this article] (2026). Transition From Faulting to Dilatant Cataclastic Flow in Carrara Marble Revealed by Acoustic Monitoring and 4D X‐Ray Imaging. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 131(8). doi: 10.1029/2026jb034160. Full text in Research Archive Show summary

  The brittle–ductile transition, typically located near the base of the seismogenic zone, controls strain localization and the evolution of physical properties, with direct implications for fluid transport and fault mechanics. However, quantitative constraints on strain partitioning and porosity evolution across this transition remain limited, particularly in low‐porosity carbonate rocks. We conducted triaxial compression experiments on dry Carrara marble at confining pressures of 5 and 100 MPa using two complementary techniques: (a) acoustic emission (AE) monitoring coupled with P‐wave velocity measurement, and (b) in situ X‐ray microtomography combined with digital volume correlation (DVC). AE activity remains low at all pressures, with source mechanisms becoming increasingly compaction‐dominated at the highest confinement. P‐wave velocities fall markedly during deformation by up to 60% at 5–10 MPa, ∼50% at 40 MPa, and ∼40% at 100 MPa, reflecting pervasive microcrack development. DVC reveals that the proportion of dilative volumetric strain decreases with confinement from nearly 90% at 5 MPa to 50% at 70–90 MPa, yet dilation remains a major component and is comparable to compaction even at the highest pressures. X‐ray–derived bulk porosity increases from <1% to ≈1.5% at low confinement prior to failure, and to 10% at higher confinements, indicating substantial porosity generation during distributed dilatant cataclastic flow. Together, these results provide the first quantitative link between P‐wave velocity reduction, volumetric strain partitioning, and transient porosity generation across the brittle to semi‐ductile transition, revealing how the interplay of dilation and compaction governs both elastic properties and strain localization in low‐porosity crystalline carbonate.

• 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.

• Aiken, John Mark; Barras, Fabian; Renard, Francois; Hirth, Greg; Kelemen, Peter B. & Sohn, Robert A. (2026). Slowly Migrating Fracture Swarms in an Actively Serpentinizing Borehole. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 131(2). doi: 10.1029/2025jb032133. Full text in Research Archive Show summary

  Peridotite rocks are primary targets for engineered geological carbon sequestration efforts because the carbon in ‐bearing fluids is transferred to the rock in the form of carbonate minerals during alteration reactions. Sequestration efforts must necessarily open fractures in the rocks surrounding a pumped borehole, but the current understanding of fracture growth during serpentinization of peridotite is limited to theoretical models and laboratory experiments on small samples. We deployed hydrophone arrays in peridotite boreholes established by the Oman Drilling Program and detected downward migrating fracture swarms that represent the first field observations of fracture growth in a serpentinizing rock. More than 2 years after the boreholes were established, we detected four, downward migrating tensile fracture swarms during an interval of elevated pore pressure following large rain events. All of the swarms occurred within a partially confined section of the local aquifer, beginning at a depth of 170 m and migrating to the bottom of the 400 m‐deep hole at average rates of 6–20 cm.. We demonstrate that pore fluid processes can explain both the triggering of the tensile fracture swarms and their slow migration rates. Our results indicate that the tip of fractures propagating away from the borehole maintained near‐critical states over time such that relatively small increases in fluid pressure triggered tensile fracturing episodes, indicating that carbon sequestration efforts in mafic rocks should be able to open fractures and expose fresh rock to mineralization.

• 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
• Linga, Gaute; Pierce, Kevin; Moura, Marcel; Mathiesen, Joachim; Renard, Francois & Borgne, Tanguy Le (2026). Dynamic multiphase flow triggers chaotic mixing in porous media. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 123(34). doi: 10.1073/pnas.2612884123. Full text in Research Archive

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• Barras, Fabian; Aspaas, Andreas Grøvan; Aharonov, Einat & Renard, Francois (2026). Unveiling the role of seepage forces in the acceleration of frictional creep in fluid-saturated shear zone. doi: 10.5194/egusphere-egu26-17167. Full text in Research Archive Show summary

  How fluid impact frictional slip is a central question in various geological settings, from tectonic faults to friction at the base of glaciers. In this work, we study the impact of fluid infiltration on the creep dynamics of the shear zone located at the base of a densely monitored landslide in Western Norway. In Åknes, approximately 50 million cubic meter of rock mass continuously creeps over a shear zone made of rock fragments, with seasonal accelerations that strongly correlate with rainfall. In this natural laboratory for fluid-induced frictional creep, unprecedented monitoring equipment reveals low fluid pressure across the shear zone, thereby challenging the conventional theory of fluid-driven instability in landslides. Here, we show that a generic micromechanical model can disentangle the effects of fluid flow from those of fluid pressure, and demonstrate that seepage forces applied by channelized flow along the shear zone are the main driver of creep accelerations. We conclude by discussing the significance of seepage forces, the implications for hazard mitigation and the broader applicability of our model to various geological contexts governed by friction across saturated shear zones.

• Dziadkowiec, Joanna; Linga, Gaute; Dunkel, Kristina G.; Valtiner, Markus & Renard, Francois (2026). In-situ, real-time replacement of calcite under geometrical confinement. doi: 10.5194/egusphere-egu26-3925. Full text in Research Archive Show summary

  Mineral replacement by dissolution-precipitation reactions that occur under confinement critically influences subsurface deformation by modifying rock porosity, permeability, and cohesion, and by inducing fracturing. Yet real-time, experimental observations of these phenomena at the nano- to microscale remain insufficient. In this work, we follow the in-situ replacement of confined calcite crystal using a surface force apparatus (SFA) technique. Calcite undergoes dissolution under low pH conditions, followed by replacement into three various Ca-minerals: calcium oxalate, calcium sulfate (gypsum), or calcium phosphate (brushite), depending on the initial composition of the solution. We monitor these reactions in real time, map the spatial distribution of precipitates as a function of confinement gap size, and evaluate how epitaxy between the secondary phases and the parent calcite governs preferred nucleation and growth sites. In addition, we measure forces that act on the confining pore wall during the replacement and estimate the associated crystallization pressures. This work contributes to the understanding of the mineral growth under confinement and its consequences for porous rock integrity, with immediate relevance to subsurface fluid and gas storage operations, where rapid mineralization is common.

• Guren, Marthe Grønlie; Bore, Sigbjørn Løland; Renard, Francois & Sveinsson, Henrik Andersen (2026). Energy dissipation at the atomic scale explains how fracture energy depends on crack velocity in silica glass. arxiv.org. doi: 10.48550/ARXIV.2605.03457. Full text in Research Archive Show summary

  The fracture energy of brittle materials rises with crack velocity, and this effect is typically attributed to surface roughening from path instabilities. Here we show, using molecular dynamics simulations of silica glass with a first-principles machine learned interatomic potential, that the structural fracture energy rises by up to 33 % already below the branching threshold, showing that fracture energy is not a constant material property. This rise in fracture energy is roughly equally partitioned between an increase in the intrinsic surface energy density and nanoscale roughening that increases the real fracture surface area. Results demonstrate that dynamic fracture in silica glass increases the fracture energy not merely by creating more apparent surface, but also by creating a fundamentally different surface at the nanoscale.

• 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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