Fabian Barras

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Richart, Nicolas; Anciaux, Guillaume; Gallyamov, Emil; Frérot, Lucas; Kammer, David & Pundir, Mohit [Vis alle 15 forfattere av denne artikkelen] (2024). Akantu: an HPC finite-element library for contact and dynamic fracture simulations. Journal of Open Source Software (JOSS). 9(94), s. 1–7. doi: 10.21105/joss.05253. Fulltekst i vitenarkiv Vis sammendrag

  Complex, nonlinear, and transient phenomena are at the heart of modern research in mechanics of materials. For example, the buildup and release of elastic energy at geological fault is what causes earthquakes, and the intricate details of the slip zone, the propagation of slip fronts and waves radiated through the various geological media are still active areas of research (Kammer et al., 2012, 2014; Roch et al., 2022). Similarly, understanding fracture in heterogeneous materials such as concrete, masonry or ceramics necessitates the modeling of interaction of crack fronts with complex materials (A. I. Cuba Ramos et al., 2018; Taheri Mousavi et al., 2015; Yilmaz et al., 2017), the representation of residual shear stresses in the contact of newly-formed crack surfaces (Pundir & Anciaux, 2021; Zhang et al., 2017), and the accurate characterization of transient dynamics (Corrado & Molinari, 2016; Vocialta et al., 2018) and material structure evolution (A. I. Cuba Ramos et al., 2018; Gallyamov et al., 2020). The finite-element method is now ubiquitous in virtually all areas of solid mechanics. With meticulous care on code architecture and performance, we show that our finite-element library Akantu can handle the requirements mentioned above for state-of-the-art research in mechanics of materials. Akantu is designed from the ground up for high-performance, highly distributed computations, while retaining the necessary flexibility to handle: • crack propagation with cohesive elements • non-local damage models • plastic and visco-plastic constitutive laws • large deformations • contact constraints (including rate and state friction) • interaction between contact and cohesive elements (residual crack shear strength)

• Barras, Fabian; Thøgersen, Kjetil; Aharonov, Einat & Renard, Francois (2023). How Do Earthquakes Stop? Insights From a Minimal Model of Frictional Rupture. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 128(8). doi: 10.1029/2022JB026070. Fulltekst i vitenarkiv Vis sammendrag

  The question “what arrests an earthquake rupture?” sits at the heart of any potential prediction of earthquake magnitude. Here, we use a one-dimensional, thin-elastic-strip, minimal model, to illuminate the basic physical parameters that may control the arrest of large ruptures. The generic formulation of the model allows for wrapping various earthquake arrest scenarios into the variations of two dimensionless variables Tk (initial dimensionless stress parameter on the fault) and Gc (dimensionless fracture energy), valid for both in-plane and antiplane shear loading. Our continuum model is equivalent to the standard Burridge-Knopoff model, with an added characteristic length scale, H, that corresponds to either the thickness of the damage zone for strike-slip faults or to the thickness of the downward moving plate for subduction settings. We simulate the propagation and arrest of frictional ruptures and derive closed-form expressions to predict rupture arrest under different conditions. Our generic model illuminates the different energy budget that mediates crack- and pulse-like rupture propagation and arrest. It provides additional predictions such as generic stable pulse-like rupture solutions, stress drop independence of the rupture size, the existence of back-propagating fronts, and predicts that asymmetric slip profiles arise under certain pre-stress conditions. These diverse features occur also in natural earthquakes, and the fact that they can all be predicted by a single minimal framework is encouraging and pave the way for future developments of this model.

• Pomyalov, Anna; Barras, Fabian; Roch, Thibault; Brener, Efim A. & Bouchbinder, Eran (2023). The dynamics of unsteady frictional slip pulses. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 120(34). doi: 10.1073/pnas.2309374120. Fulltekst i vitenarkiv
• Paglialunga, Federica; Passelègue, François X.; Brantut, Nicolas; Barras, Fabian; Lebihain, Mathias & Violay, Marie (2022). On the scale dependence in the dynamics of frictional rupture: Constant fracture energy versus size-dependent breakdown work. Earth and Planetary Science Letters. ISSN 0012-821X. 584. doi: 10.1016/j.epsl.2022.117442. Fulltekst i vitenarkiv Vis sammendrag

  Potential energy stored during the inter-seismic period by tectonic loading around faults is released during earthquakes as radiated energy, frictional dissipation and fracture energy. The latter is of first importance since it is expected to control the nucleation, the propagation and the arrest of the seismic rupture. On one side, the seismological fracture energy estimated for natural earthquakes (commonly called breakdown work) ranges between 1 J/m2 and tens of MJ/m2 for the largest events, and shows a clear slip dependence. On the other side, recent experimental studies highlighted that, concerning rupture experiments, fracture energy is a material property (energy required to break the fault interface) independently of the size of the event, i.e. of the seismic slip. To reconcile these contradictory observations and definitions, we performed stick-slip experiments, as analog for earthquakes, in a bi-axial shear configuration. We estimated fracture energy through both Linear Elastic Fracture Mechanics (LEFM) and a Cohesive Zone Model (CZM) and through the integration of the near-fault stress-slip evolution. We show that, at the scale of our experiments, fault weakening is divided into a near-tip weakening, corresponding to an energy of few J/m2, consistent with the one estimated through LEFM and CZM, and a long-tailed weakening corresponding to a larger energy not localized at the rupture tip, increasing with slip. Through numerical simulations, we demonstrate that only near-tip weakening controls the rupture initiation and that long-tailed weakening can enhance slip during rupture propagation and allow the rupture to overcome stress heterogeneity along the fault. We conclude that the origin of the seismological estimates of breakdown work could be related to the energy dissipated in the long-tailed weakening rather than to the one dissipated near the tip.

• Roch, Thibault; Barras, Fabian; Geubelle, Philippe H. & Molinari, Jean-François (2022). cRacklet: a spectral boundary integral method library for interfacial rupture simulation. Journal of Open Source Software (JOSS). 69(7). doi: 10.21105/joss.03724. Fulltekst i vitenarkiv Vis sammendrag

  The study of dynamically propagating rupture along interfaces is of prime importance in various fields and system sizes, including tribology (nm to μm), engineering (mm to m) and geophysics (m to km) (Armstrong-Hélouvry et al., 1994; Ben-Zion, 2008; Vanossi et al., 2013). Numerical simulations of these phenomena are computationally costly and challenging, as they usually require the coupling of two different spatio-temporal scales. A fine spatial discretization is needed to represent accurately the singular fields associated with the rupture edges. Besides, the problems of interest usually involve a larger length scale along which rupture will propagate driven by long-range traveling elastic waves. The physical phenomena at play also occur at different timescales, from the slow process of rupture nucleation to the fast propagation of crack front close the elastic wave speeds. Large and finely discretized spatio-temporal domains are required, which are computationally costly. In addition, the behavior of such interfaces can be highly non-linear thus increasing the problem complexity. The use of boundary integral methods reduces the dimensionality of the problem. This enables to focus the computational efforts on the fracture plane and allows for a detailed description of the interfacial failure processes.

• Barras, Fabian; Aghababaei, Ramin & Molinari, Jean-François (2021). Onset of sliding across scales: How the contact topography impacts frictional strength. PHYSICAL REVIEW MATERIALS. 5(2). doi: 10.1103/PhysRevMaterials.5.023605. Fulltekst i vitenarkiv
• Thøgersen, Kjetil; Aharonov, E.; Barras, Fabian & Renard, Francois (2021). Minimal model for the onset of slip pulses in frictional rupture. Physical Review E (PRE). ISSN 2470-0045. 103(5). doi: 10.1103/PhysRevE.103.052802. Fulltekst i vitenarkiv
• Passelègue, François X.; Almakari, Michelle; Dublanchet, Pierre; Barras, Fabian; Fortin, Jérôme & Violay, Marie (2020). Initial effective stress controls the nature of earthquakes. Nature Communications. 11(1). doi: 10.1038/s41467-020-18937-0. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures. However, the origin of this variation of the rupture velocity in nature as well as the physics behind it is still debated. Here, we first highlight how the different types of fault slip observed in nature appear to stem from the same physical mechanism. Second, we reproduce at the scale of the laboratory the complete spectrum of rupture velocities observed in nature. Our results show that the rupture velocity can range from a few millimetres to kilometres per second, depending on the available energy at the onset of slip, in agreement with theoretical predictions. This combined set of observations bring a new explanation of the dominance of slow rupture fronts in the shallow part of the crust or in areas suspected to present large fluid pressure.

• Barras, Fabian; Aldam, Michael; Roch, Thibault; Brener, Efim A.; Bouchbinder, Eran & Molinari, Jean-François (2020). The emergence of crack-like behavior of frictional rupture: Edge singularity and energy balance. Earth and Planetary Science Letters. ISSN 0012-821X. 531. doi: 10.1016/j.epsl.2019.115978. Fulltekst i vitenarkiv
• Rezakhani, Roozbeh; Barras, Fabian; Brun, Michael & Molinari, Jean-François (2020). Finite element modeling of dynamic frictional rupture with rate and state friction. Journal of the Mechanics and Physics of Solids. ISSN 0022-5096. 141, s. 1–22. doi: 10.1016/j.jmps.2020.103967. Fulltekst i vitenarkiv
• Barras, Fabian; Aldam, Michael; Roch, Thibault; Brener, Efim A.; Bouchbinder, Eran & Molinari, Jean-François (2019). Emergence of Cracklike Behavior of Frictional Rupture: The Origin of Stress Drops. Physical Review X. 9(4). doi: 10.1103/PhysRevX.9.041043. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv
• Kleven, Alette; Barras, Fabian & Galland, Olivier (2025). Tensile versus shear failure of the host rocks at the tip of a pressurized dyke. Fulltekst i vitenarkiv Vis sammendrag

  Sheet intrusions are the most fundamental magma pathways through the crust. Field observations suggest a variety of dyke propagation modes, ranging from tensile failure of the host rock in agreement with the Linear Elastic Fracture Mechanics (LEFM) theory, to shear failure of the host rock in agreement with the viscous indenter model. Under which conditions tensile versus shear failure occur at the propagating dyke tips is currently unknown. This is a key question as the LEFM and viscous indenter dyke propagation mechanisms may produce drastically distinct geophysical and geodetic signals. Here we present a Finite Element Model (FEM) that simulates the elastoplastic behavior of crustal rocks following a Drucker-Prager yield criterion. The host rock is deformed by the increasing pressure in an elliptical dyke until failure is reached at its tip. In our elastoplastic model, either tensile or shear failure occurs, depending on the host rock cohesion, the dyke dimension and depth. By exploring the parameter space, we built phase diagrams to map under which conditions tensile versus shear failure occur at dyke tips. Our results show that shear failure is favored when (1) the host rock cohesion is low, and/or (2) the dyke tip is deep and/or (3) the thickness-to-length aspect ratio of the dyke is high. Our study and phase diagram provide insights for the interpretation of geophysical and geodetic data collected at active volcanoes.

• Lanza, Federico; Baldelli, Beatrice; Linga, Gaute; Barras, Fabian & Flekkøy, Eirik Grude (2024). The Cooling Instability. Fulltekst i vitenarkiv
• Lanza, Federico; Baldelli, Beatrice; Linga, Gaute; Barras, Fabian & Flekkøy, Eirik Grude (2024). Dynamic instability of a temperature-dependent viscous fluid in a Hele-Shaw cell. Fulltekst i vitenarkiv
• Lanza, Federico; Baldelli, Beatrice; Linga, Gaute; Barras, Fabian & Flekkøy, Eirik Grude (2024). Simulating finger structures that may form when a warm liquid (lava) cools and becomes more viscous during flow through a fracture. Fulltekst i vitenarkiv

Se alle arbeider i NVA