• 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.

• Lanza, Federico; Linga, Gaute; Barras, Fabian & Flekkøy, Eirik G. (2026). Thermoviscous instability of flow in a weakly heat-conducting channel. Physical Review Fluids. 11(4). doi: 10.1103/gjnj-b4bl. Full text in Research Archive
• Barras, Fabian; Aharonov, Einat & Renard, Francois (2025). A Minimal Model Illuminates the Physics of Pulse-Like Seismic Rupture and Oscillatory Slip Rates in Damaged Faults. Geophysical Research Letters. ISSN 0094-8276. 52(4). doi: 10.1029/2024GL111189. Full text in Research Archive Show summary

  Fault zones are often surrounded by a damage zone that exhibits lower seismic velocities than the wall rock, influencing earthquake propagation and arrest. We present a one-dimensional minimal model of frictional rupture that approximates the elastodynamics of a fault embedded within a damage zone. This model predicts two families of steady-state rupture solutions: an overdamped regime, describing a crack-like rupture, and an underdamped regime with oscillating slip-rate in the wake of the rupture, which promotes pulse-like dynamics. The minimal model contains two free parameters: the pre-stress on the fault, and the seismic velocity reduction in the damage zone. We present how the one-dimensional prediction is consistent with previously published two-dimensional simulations and discuss the applicability of our results to natural observations, identifying the preferred rupture style as function of structure of the fault zone, and the geological consequences of oscillatory slip in the wake of pulse-like ruptures.

• Barras, Fabian & Brantut, Nicolas (2025). Shear localisation controls the dynamics of earthquakes. Nature Communications. 16(1). doi: 10.1038/s41467-024-55363-y. Full text in Research Archive Show summary

  Earthquakes are produced by the propagation of rapid slip along tectonic faults. The propagation dynamics is governed by a balance between elastic stored energy in the surrounding rock, and dissipated energy at the propagating tip of the slipping patch. Energy dissipation is dictated by the mechanical behaviour of the fault, which is itself the result of feedbacks between thermo-hydro-mechanical processes acting at the mm to sub-mm scale. Here, we numerically simulate shear ruptures using a dual scale approach, allowing us to couple a sub-mm description of inner fault processes and km-scale elastodynamics, and show that the sudden localisation of shear strain within a shear zone leads to the emergence of classical cracks driven by a constant fracture energy. The fracture energy associated to strain localisation is substantially smaller than that predicted in theoretical and numerical models assuming uniform shearing within the shear zone. We show the existence of a unique scaling law between the localised shearing width and the rupture speed. Our results indicate that earthquakes are likely to be systematically associated to extreme strain localisation.

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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.

• Barras, Fabian & Brantut, Nicolas (2026). Bridging inner fault shear localisation and the propagation of earthquake rupture. doi: 10.5194/egusphere-egu26-15062. Full text in Research Archive Show summary

  Earthquakes leave different types of records that help decipher their dynamics. At the large scale monitored by remote sensing and seismic data, earthquakes arise from the propagation of rapid slip along tectonic faults, exhibiting rupture dynamics reminiscent of those driving shear fracture or slip fronts in stick-slip experiments. At the scale of the fault core, fieldwork revealed how the zone actively deformed during an earthquake is often extremely thin and that shear strains are highly localised.In this work, we numerically simulate shear ruptures using a dual-scale approach, allowing us to couple a sub-millimetre description of inner fault processes and kilometre‑scale elastodynamics. Our results demonstrate how rapid strain localisation across a layer of fault gouge creates a sudden drop in the shear stress bearing capacity, producing earthquake rupture that closely follows fracture mechanics description. We quantify how the fracture energy governing rupture propagation is substantially smaller than that predicted by models that do not account for strain localisation. We show the existence of a unique scaling law between the localised shearing width and the rupture speed. Our results bring new insights on the multiscale mechanics that produces seismic rupture and indicate that earthquakes are likely to be systematically associated to extreme strain localisation.

• Lanza, Federico; Linga, Gaute; Barras, Fabian; Khobaib, Khobaib; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2025). From Carbopol to magma: challenges in complex flows through porous and confined media. Full text in Research Archive

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