Fault geometric heterogeneities such as roughness, stepovers, or other irregularities are known to affect the spectra of radiated seismic waves that result from dynamic slip on a fault. To investigate the effect of normal stress heterogeneity on radiated spectra, we created a laboratory fault with a single, localized bump by utilizing the compliance and machinability of poly methyl methacrylate (PMMA). By varying the normal stress on the bump and the fault-average normal stress, we produced earthquake-like ruptures that ranged from smooth, continuous ruptures to complex ruptures with variable rupture propagation velocities, slip distributions, and mechanical stress drops. We used an array of eight piezoelectric sensors to measure vertical ground motions calibrated to determine source spectra and PGA for individual events. High prominence bumps produced complex events that radiated more high frequency energy, relative to low frequency energy, than continuous events without a bump. In complex ruptures, the radiated high frequency energy was spatially variable and correlated with local variations in peak slip rate and maximum mechanical stress drop caused by the bump. Continuous ruptures emitted spatially uniform bursts of high frequency energy as the rupture propagated along the fault. Near-field peak ground acceleration (PGA) measurements of complex ruptures show nearly an order-of-magnitude higher PGA near the bump than elsewhere. We propose that for natural faults, geometric heterogeneities may be a plausible explanation for commonly observed order-of-magnitude variations in near-fault PGA.
How to cite: Cebry, S. B. L. and McLaskey, G.: Heterogeneous high frequency seismic radiation from complex ruptures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3342, https://doi.org/10.5194/egusphere-egu25-3342, 2025.
We aim to determine the feedback between fault dynamics and fault gouge structures by examining gouge structures that formed during rupture and slip of initially intact granite under upper crustal conditions. Experiments were conducted under quasi-static (3·10-5 mm/s), weakly dynamic (0.27 mm/s) and fully dynamic (≫1.5 mm/s) conditions, with or without fluids, and limited slip displacement (max. 4 mm). The extent in gouge amorphisation positively correlates with deformation rate, and we detected evidence of melting, e.g., magnetite nanograins, associated with the highest deformation rates. Gouge nanostructure is directly correlated to power dissipation rather than total energy input. The presence of amorphous material is shown to have no detectable impact on the strength evolution during rupture. We highlight that gouge textures, generally associated with large displacements and/or elevated pressure and temperature conditions, can form during small slip events (Mw <2) in the upper crust from initially intact materials.
How to cite: Incel, S., Ohl, M., Aben, F., Plümper, O., and Brantut, N.: Nanostructures as indicator for deformation dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17710, https://doi.org/10.5194/egusphere-egu25-17710, 2025.
Subduction zone thrust fault systems accommodate deformation and guide the dynamics of converging tectonic plates. Investigating the frictional, healing, and deformation mechanisms at shallow depths within these zones is important for enhancing models of fault zone mechanics, slip behavior, and material transfer processes, as well as for understanding the nucleation and propagation of megathrust earthquakes. The Gova Fault Zone (GFZ), located within the basal portion of the Sestola-Vidiciatico Unit (SVU) in the Northern Apennines (Italy), offers a unique opportunity to examine the frictional properties, healing dynamics, and deformation processes within an exhumed erosive subduction channel.
The GFZ consists of multiple thrust surfaces that juxtapose highly folded and strained phyllosilicate-rich sediments derived from the upper plate (Marmoreto Marls, Fiumalbo Shales, FIU, and Civago Marls Fms., CIV) onto foredeep turbidites (Gova Sandstone Fm, GOV) of the lower plate.
We sampled the rocks in across the GFZ transect from the footwall GOV sandstones into the SVU shear zone, a sheared Civago marls and Fiumalbo shales.
Fault rocks were reduced to gouge and sheared in a rotary shear apparatus equipped with a hydrothermal vessel (RoSA+HYDROS, University of Padova) under an effective normal stress of 20 MPa and fluid pressure of 6 MPa, at both 25°C, and 200°C. We measured the friction and the time-dependent recovery of frictional strength during simulated interseismic periods (i.e., the healing).
The footwall GOV sandstone gouges are dominated by cataclastic processes, are frictionally strong and their friction increase from μ = 0.49 at 25°C to µ = 0.57 at 200° C. They are also characterized by positive healing and a transition from stable slip to stick-slip at 200° C.
The hangingwall rocks are frictionally weaker: the CIV marls show μ = 0.27 (25°C)-0.31 (200° C) and the FIU shales µ = 0.2 (25°C)-0.25 (200° C), display null/negative frictional healing rates. Both rocks maintained stable sliding, facilitated by phyllosilicate lamellae reorientation and buckling. The CAT, show intermediate friction µ = 0.37 (25°C)-0.42 (200° C) but negative healing rate slip behavior dominated by stable sliding.
The measured in the experiments of the footwall sandstones would, in nature, force strain to migrate into the weaker lithologies of the hangingwall. This “migration” of strain favors (1) the development of thrust surfaces within the hangingwall, such as the FIU on CIV contact, and contributes (2) to erosion, enabling the transfer of material from the upper plate to the lower plate. The positive frictional healing and stick-slip behavior at 200° C in the siliciclastic fault rocks (GOV) suggest a role of the footwall in favoring seismic slip nucleation. Conversely, the weakness and lack of frictional healing suggest a predominantly aseismic or slow slip behavior in the phyllosilicate-rich lithologies. Collectively, we found that frictional and microstructural heterogeneities between subducting sediments and the tectonic mélange at shallow depths may control the erosional vs. accretional character of subduction zones and be responsible for complex slip behavior within the frontal thrusts of subduction zones.
How to cite: Diamanti, R., Salvadori, L., Remitti, F., Mittempergher, S., Molli, G., Di Toro, G., and Tesei, T.: Frictional properties and healing in sedimentary subduction fault zones: insights from the Sestola-Vidiciatico unit, Northern Apennines., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17462, https://doi.org/10.5194/egusphere-egu25-17462, 2025.
Laboratory investigations into the behavior of fault zones have been a significant focus in experimental rock mechanics over the past decades. Various approaches have been developed, ranging from analog models to testing natural samples in triaxial cells. The primary goal of the latter is to infer the physical mechanisms responsible for failure under realistic conditions encountered in natural settings, albeit on small sample sizes (e.g., centimeter scale). In contrast, analog modeling aims to replicate similar mechanical behavior by applying scaling laws to geometry and material properties.
To address the spatial scale limitations of classical rock mechanics, we developed new experiments that bridge the gap between traditional rock mechanics and analog experiments. These experiments utilize the unique capabilities of the DIMITRI setup, a giant true-triaxial apparatus (1.5m × 1.5m × 1m). Due to the size of this experimental device, the maximum stress it can apply is limited to 2 MPa per principal stress. Consequently, we chose polystyrene as an analog for rocks. The low elastic properties of polystyrene slow down physical processes, enabling comprehensive observation of rupture phenomena, from initiation to failure arrest. Our objective is to investigate the interplay between different types of slip occurring along the interface.
In this study, we conducted stick-slip experiments on large-scale polystyrene blocks with a pre-cut surface area of 1.5 m². We applied shortening rates ranging from 1 to 10 mm/min. Our experiments successfully reproduced stick-slip behavior, allowing us to observe variations in frictional behavior along the interface and identify different types of slip, from slow slip to dynamic slip.
How to cite: Bonnelye, A., Gouedar, A., and Faure-Catteloin, D.: PolystyQuakes : what can we learn from the use of polystyrene as analogue to earthquakes?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16260, https://doi.org/10.5194/egusphere-egu25-16260, 2025.
The geometrical roughness of faults results in significant stress heterogeneity across various length scales, thus affecting rupture and sliding behavior during earthquakes. The dilatancy behavior on rough joints also becomes much more complicated than on planar faults. Whether dilation or compaction will occur on rough faults, especially those with large asperity heights, during interseismic and seismic slips is still an open question.
Here, we perform laboratory shear tests on rough faults with millimeter-scale asperity heights and analyze the four types of dilation or compaction behavior observed during stick-slip cycles. In the stick phases, dilatancy behavior inferred from the asperity contacts agrees well with the variation of normal displacement. The locations of acoustic emission (AE) events are also consistent with the potential surface damage regions estimated from the evolution of asperity contacts at various shearing displacements. Stick-slip events with compaction-dominant interseismic slip usually occur at large shear displacements on interlocking faults when overriding high asperities. In those stick-slip events, the proportion of large-magnitude AEs is lower, resulting in higher Gutenberg–Richter b values. A generalized schematic model is also proposed for the complex dilatancy behavior during stick-slip cycles.
The experimental results provide new insights into the effects of fault roughness on shear-induced dilatancy behavior and serve as valuable benchmarks for our numerical simulations considering visible contact evolutions during shear sliding on rough faults.
How to cite: Chai, S., Su, B., Zou, Y., and Zhao, Q.: Dilation or compaction? Laboratory insights into the role of fault roughness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7873, https://doi.org/10.5194/egusphere-egu25-7873, 2025.
Understanding earthquakes mechanisms still represents a challenge, motivated by the large consequences of the numerous earthquakes occurring each year. The complexity of fault zones and fault behaviour requests to make some simplifications and to down-scale the studied system. In our work we borrow from the tribological approach the pin-on-disk experiment so that the two rough surfaces in contact through a series of asperities fault concept is downscaled to a single asperity sliding on a rough surface. The single asperity response to shearing induced by sliding and the evolution of friction are studied closely to understand the behaviour of the down-scaled fault, especially when the velocity is changing. Moreover, mono-asperity experimental tests are an effective way to construct new friction laws for numerical simulations.
The original experimental apparatus consists in a centimetric pin with a hemispherical extremity representing the fault asperity while a large flat rotating disk stands for the opposite surface of the experimental fault. Both pieces are made in the same carbonate rock (Carrara white marble) with controlled roughness. Under co-seismic conditions (contact size, contact normal stress) and with a rough track with presence of granular gouge, the lab-fault is submitted to different velocities (from 0.001 m/s up to 1m/s). A number of high-sampling-rate sensors are used to constrain the observation of the asperity-rough track contact during the simulated seismic events. Moreover, complete post-mortem analyses of the contact surfaces with optical microscopy, SEM and roughness images allow to quantify the mechanisms and to reconstruct friction scenarios in accordance with the time-series acquired during tests. A quasi 2D numerical twin is also created with the elementary discrete method software MELODY, in order to compare the different features observed on the pin or on the track.
In this present work, we focus on the change of wear mechanisms in the lab-fault due to changes in sliding velocity. Independently of the normal load applied, the Carrara white marble asperity-track system experiences weakening velocity due to frictional heating. The friction coefficient evolution during the co-seismic events and the post-mortem analyses put in contrast two regimes. At low velocity, the carbonate rock lab fault wears off at a constant rate producing a large amount of granular gouge. At high velocity, the contact surfaces are covered by viscous sintered material, which can be called mirror surfaces.
How to cite: Clerc, A., Mollon, G., Ferrieux, A., Lafarge, L., and Saulot, A.: Velocity influence on the friction and wear of a single-asperity lab-fault, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6563, https://doi.org/10.5194/egusphere-egu25-6563, 2025.
Cyclic fluid injection for industrial purposes within fault zones are commonly imposed, since they are observed to stabilize induced seismicity, often inducing aseismic slip along fault surfaces, without immediate seismic energy release (Zang et al., 2018; Noël et al., 2019; Ji et al., 2021a, 2021b, 2022). Even though dynamic variations of effective normal stress on fault zones due to both natural and anthropogenic causes are common (Chen et al., 2024), the impact of the perturbations and their frequencies on fault strength is less explored (Savage and Marone, 2007; Ferdowsi et al., 2015; Noël et al., 2019). The frequency of pore-pressure changes are expected to impose a characteristic timescale, controlling the crossover from a drained to an undrained response, which in turn will promote markedly different deformation modes and rates (Passelègue et al., 2018).
In this work we present results from a coupled hydromechanical-discrete element model that simulates the response of a pre-stressed, fully saturated fault, filled with a granular fault gouge, subject to cyclic pore-pressure variations across frequencies of three orders of magnitude. For lower frequencies we see nucleation-arrest-nucleation dynamics within the granular rupture and for higher frequency we observe cyclic creep, both driven by pore-pressure perturbations. Within the frequency parameter space we see a crossover of the slip modes as we increase frequency, lower frequencies show unstable failure, while higher frequencies show creep. Our results might account for a) fluid induced slip stability in cyclic injection scenarios (higher frequencies) and b) low-frequency dynamic triggering of earthquakes.
How to cite: Parez, S., Sarma, P., and Aharonov, E.: Response of a fluid-saturated fault gouge to frequency varied cyclic pore-pressure variations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4426, https://doi.org/10.5194/egusphere-egu25-4426, 2025.
Laboratory studies have demonstrated that faults undergo dynamic weakening during large displacements (>1 m) at seismic slip velocities (>0.1 m/s). However, the role of this weakening in small-displacement induced earthquakes (M 3–4), such as those in the Groningen Gas Field (the Netherlands), remains unclear. To address this, we conducted seismic slip-pulse experiments on Slochteren sandstone gouges (SSG), derived from the gas reservoir, using a rotary-shear apparatus to provide decimeter-scale constraints on the dynamic fault slip of quartz-rich gouges. Pre-sheared gouge layers, confined between ~1.5 mm thick sandstone host blocks, were subjected to slip pulses under initial effective normal stresses of 4.9–16.6 MPa and pore fluid pressures of 0.1 and 1 MPa under undrained conditions. The experiments achieved peak velocities of 1.8 m/s, accelerations up to 42 m/s², and displacements of 7.5–15 cm, using either dry Argon or water as pore fluid at ambient temperatures. Our results reveal that water-saturated gouges weaken rapidly from a peak friction of ~0.7 to ~0.3, accompanied by early fast dilatancy followed by slower ongoing dilation, with minimal dependence on normal stress, slip acceleration, or displacement. In contrast, Argon-filled samples exhibited only minor weakening. Microstructural analysis shows no systematic relationship between the width of the principal slip zone (PSZ) and frictional work or power input densities, indicating that wear or heat production alone does not control PSZ growth. Instead, our thermo-hydro-mechanical (THM) numerical modeling suggests that thermal pore fluid pressurization, potentially involving water phase transitions at asperity scales, drives weakening in short-displacement, induced seismic events. To extend these small-scale laboratory findings to reservoir-scale processes, ongoing research focuses on discrete element modeling (DEM) at particle and gouge scales coupled with THM solutions. This includes calibrating the THM-DEM models at both grain and gouge scales using laboratory data from Groningen sandstone-derived samples. The calibrated models will be validated with recent data generated under fast slip conditions with varying pore fluids.
How to cite: Hung, C.-C., André, N., Aretusini, S., Spagnuolo, E., Chen, J., and Hamers, M.: Thermo-hydro-mechanical mechanisms in sandstone-derived fault gouges during simulated small-magnitude earthquakes from experiments and models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4873, https://doi.org/10.5194/egusphere-egu25-4873, 2025.
Faults can slip in diverse modes, ranging from slow, aseismic creep to dynamic, earthquake-generating rupture. Geological observations reveal that many fault zones consist of localized slip zones surrounded by a broader damage zone, where microcracks and fractures interact in complex ways. Friction laws propose that whether a fault will host a slow slip event or a fast dynamic rupture depends on the relative stiffness of these slip zones and the surrounding material. Conversely, the local stress field imposes such structures' evolution. Although the evidence for these complex interactions indicates the opportunity to incorporate this knowledge in the theoretical framework, collecting data on the spatiotemporal evolution of elastic properties at seismogenic depth is inherently challenging, leaving this possibility mostly unexplored.
Laboratory experiments provide a controlled environment for studying the evolution of fault mechanics and elastic properties. Elastic waves are governed by the same equations that relate wave speeds to dynamic moduli. Therefore, they offer a pathway to link laboratory observations to natural fault processes.
This study investigates how microstructural reorganization during fault deformation and fault zone structure formation affects fault zone stiffness and slip behavior using synthetic quartz gouge layers sheared in double-direct shear (DDS) configuration.
Our DDS setup is instrumented with piezoelectric transducers designed to generate and record predominantly compressional (P) or shear (S) waves. By carefully characterizing the source time function, we ensure that early arrivals in each recorded signal represent a single wave mode with minimal mode conversion or side reflections.
We then apply Full Waveform Inversion (FWI) to these early arrivals to reconstruct velocity models for both P- and S-waves as deformation progresses. The inverted models reveal spatiotemporal variations in the bulk and shear moduli, which we interpret as signatures of contact-area changes, grain size reduction, and other micromechanical processes relevant to frictional stability. In particular, the evolving elastic properties allow us to gauge how the local stiffness of the gouge zone evolves relative to applied stress, linking the observed velocity changes to the constitutive laws underpinning rate-and-state friction (RSF). While RSF implicitly links frictional strength to contacts dynamic through a state variable, our results illustrate how ultrasonic waveform acquisition and modeling can provide hints toward the explicit rewriting of such laws in terms of the evolution of elastic properties, an intermediate level of description easier related to micromechanical processes.
This approach highlights the potential for ultrasonic measurements in earthquake laboratory experiments to probe fault zone mechanics and outline a framework for integrating seismic imaging with frictional mechanics to better understand fault behavior across scales.
How to cite: De Solda, M., Mauro, M., Guglielmi, G., Pignalberi, F., and Scuderi, M.: Probing Fault Zone Evolution with Ultrasonic Measurements: Seismic Imaging in Laboratory Experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7148, https://doi.org/10.5194/egusphere-egu25-7148, 2025.
Accurately modeling faulting in the so-called brittle crust remains a challenge due to limitations in numerical algorithms and problems in choosing realistic constitutive models. These challenges are reflected in difficulties linking observations across scales: from laboratory to outcrop and up to regional geology.
Here we present the Geotechnical Particle Finite Element Method (P-FEM), a large-deformation numerical tool developed to capture detailed progressive failure and fracturing using a non-local formulation.
A key advantage of P-FEM is its ability to simulate localized shear bands (fault zones with finite thickness) that naturally emerge independent of mesh discretization, both in thickness and orientation. Continuous remeshing further enables the modeling of large deformations within a Lagrangian framework, and techniques used to minimize numerical diffusion help producing realistic localized shear/fault zone patterns. Additionally, P-FEM benefits from its foundation in standard finite elements, allowing to use efficient and accurate solvers (tested through years by a large community of users) and a wide library of constitutive models to simulate various geo-materials, including non-cohesive soils and fault gouges, weak porous rocks (that could develop deformation/compaction bands), and “standard” brittle-frictional-plastic materials. Multiphysics implementations including fluid and heat flow are also available but will not be specifically discussed here.
These capabilities make P-FEM particularly suited for investigating fundamental tectonic processes such as (i) fault nucleation and growth in mechanically layered materials, (ii) the interplay between faulting and folding in thrust belts, and (iii) the development of fault damage and/or process zones in materials with heterogeneous mechanical properties. Our contribution will outline the P-FEM method and discuss its application to these tectonic problems.
How to cite: Bistacchi, A., Ciantia, M., Castellanza, R., Mittempergher, S., and Agliardi, F.: Applications of the Particle Finite Element Method (P-FEM) to faulting in the brittle crust, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17832, https://doi.org/10.5194/egusphere-egu25-17832, 2025.
Posters on site: Mon, 28 Apr, 14:00–15:45 | Hall X2
On major plate-boundary fault zones, there is an expectation that large-magnitude earthquakes do not nucleate at shallow depths, but rather starting at depths of several km in the crust. This depth dependence is generally understood to be controlled by the frictional behavior of the sediments making up fault gouges, where velocity-strengthening friction and low effective stresses at shallow depths tends to produce stable fault slip. The transition to velocity-weakening rocks at seismogenic depth has been suggested to be caused by a variety of diagenetic and low-grade metamorphic processes that lithify the sediments into more competent fault rocks. Recent laboratory results on both natural fault rocks and desiccated clay-salt mixtures show that this is a viable mechanism, where velocity-weakening friction is seen in the lithified rocks having high cohesion and low porosity. A remaining open question is whether the key ingredient for velocity-weakening friction is the porosity reduction, or the mechanical cementation.
Here, we test whether porosity reduction alone can induce velocity-weakening friction in powdered Rochester shale, an otherwise velocity-strengthening sediment. We control the porosity by consolidating deionized water-saturated shale powders to a vertical stress of 86 MPa and shearing the samples under lower effective normal stresses of 0.1-10 MPa, for overconsolidation ratios (OCRs) of up to ~860. We then measure the frictional properties of our overconsolidated samples with velocity-step tests from 10-6–10-5 m/s, repeated over long displacements to account for fading of the initial consolidation state with slip.
We observe that overconsolidation induces an additional porosity reduction of 35-63%, relative to the porosity under normal consolidation. The velocity steps show predominantly velocity-strengthening friction; however, some scattered instances of velocity-weakening are observed for the highest tested OCR. Analysis of the rate- and state-dependent friction parameters shows that the velocity steps in samples with the highest OCR have both larger values of “a” and large positive values of “b”, whereas the rest of the samples show predominantly negative values of “b”. The observed pattern in “b” suggests that asperity contacts under shear, and therefore surface roughness is important. This is supported qualitatively by photos of the shear surfaces, showing that for larger OCRs, a smaller proportion of the nominal surface area is in real contact during shear. The results show that velocity-weakening friction begins to appear when the additional porosity reduction is ~55%, consistent with previous work. However, the appearance of velocity-weakening friction due solely to porosity loss may require unrealistically large OCRs, and truly unstable sliding at depth likely requires cementation by mineralization.
How to cite: Ikari, M. and Hüpers, A.: Frictional slip behavior of highly overconsolidated fault gouge, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1722, https://doi.org/10.5194/egusphere-egu25-1722, 2025.
Safe exploitation of high-enthalpy geothermal fields for energy production requires knowledge of the mechanical behavior of faults and the seismic cycle in the presence of hot, pressurized fluids. In geothermal reservoirs, fluids can exist in the liquid, liquid-vapor mixture, vapor, or supercritical fluid state. Here we investigate the frictional properties of simulated fault gouges derived from the main stratigraphic units present in Krafla Geothermal Field (Iceland) under realistic water temperature (Tf=100-400˚C) and pressure (Pf=10-30 MPa) conditions. These conditions correspond to water in the liquid, vapor, and supercritical state.
Laboratory rotary shear, slide-hold-slide (SHS) experiments at a constant effective normal stress of 10 MPa are performed on gouges prepared from non-altered basalt (Krafla Fires eruptions, 1975-1984), chlorite-altered basalt (borehole KH-6, 708.5 m borehole depth), amphibole-altered basalt (borehole IDDP-01, 1686 m borehole depth), fine-grained basaltic dyke with scarce alteration (borehole IDDP-01, 1970 m borehole depth), and rhyolite (borehole KJ-39, 1637-1646 m borehole depth). All experiments are initiated with a 5 mm run-in slip at a loading point slip rate V of 10 μm/s followed by the SHS sequence with a hold time thold increased from 3 s to 10,000 s, separated by a slip interval of 1 mm.
The frictional strength μss (friction coefficient during run-in) slightly increases with Tf in non-altered and amphibole-altered basalt and slightly decreases with Tf in chlorite-altered basalt, basaltic dyke, and rhyolite. However, for all rock types, μss is higher (μss_vap> μss_sup and μss_liq) when vapor is present (only exception, non-altered basalt with μss_sup>μss_vap> μss_liq).
The frictional healing Δμ (frictional strength recovery during holds), is highest at Tf=400˚C in vapor and supercritical water. Still, the effect of Tf and the physical states of water on frictional healing rate (β=Δμ/log(1+thold/tcutoff)) depends on rock type. In non-altered basalt, β increases with Tf but decreases in vapor water; in chlorite-altered basalt and basaltic dyke, β increases with Tf and is independent of the physical state of water; in amphibole-altered basalt and rhyolite, β is independent of both Tf and the physical state of water. However, systematic microanalysis of the deformed gouges is required to understand the underlying mechanisms.
Lastly, for measured constant machine stiffness in this Tf-Pf range, all tested gouges show stable sliding (creep) at Tf=100˚C but become unstable (stick-slip) at Tf=200˚C (basaltic dyke) and Tf=300˚C (other rock types) regardless of the physical states of water. The highest stress drops during stick-slip are measured in supercritical water (non-altered basalt) or vapor (all the other gouges). Consistent with the seismological observations, our laboratory data show that the fault/fracture network in Krafla reservoir is less prone to nucleate earthquakes in the shallow hydrothermal system (Tf~170˚C, < 1 km depth), with most earthquakes located in the deep hydrothermal system (Tf≥300˚C, 1-2 km depth).
In conclusion, both temperature and the physical states of water should be considered when interpreting the seismicity in geothermal fields.
How to cite: Wu, W.-H., Feng, W., Gomila, R., Tesei, T., Violay, M., Mortensen, A. K., and Di Toro, G.: The Effect of Temperature and Physical State of Water on the Frictional Properties of Gouges from Krafla Geothermal Field (Iceland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13704, https://doi.org/10.5194/egusphere-egu25-13704, 2025.
Ophicalcites (carbonated ultramafic rocks) are commonly found when serpentinized mantle rocks are exposed to fluid-rock interaction in settings such as slip and damage zone of mid ocean ridges, transform faults and subduction zones. In this study, we analyze the frictional strength and healing properties of ophicalcites under hydrothermal conditions because of their possible role in the nucleation of “fast” (i.e., earthquakes) and slow slip events.
The ophicarbonates used in this study belong to the exhumed ophiolitic unit of Eastern Elba Island (Italy). The hand samples are black, red, and purple ophicarbonates and include veined breccias and cataclasites. The mineral assemblages, determined through optical microscopy and quantitative (Rietveld) X-ray powder diffraction, consist of serpentine (lizardite and chrysotile with rare relicts of pyroxene and olivine), talc and calcite veins. Hematite is only found in the red ophicalcite.
We conducted slide-hold-slide experiments with a rotary-shear apparatus coupled with a hydrothermal vessel (ROSA-HYDROS, Padua University, Italy) on a synthetic fault gouge derived from a red natural ophicalcite cataclasite with a composition of 26.9% lizardite and chrysotile, 12.3% talc, 57.6% calcite, 2.9% hematite and traces of smectite. The experiments were performed at an effective normal stress (σneff = σn - Pp) of 20 MPa, a fluid pressure (Pp) of 6 MPa, constant slip velocity of 10 µm/s between the holds (which lasted from 10 to 10.000 s) and temperatures ranging from 20 to 400°C. Our results show that, the “serpentinite” component dominates the bulk friction and the healing behaviour. For T≤ 200°C and in the presence of water in liquid state, the friction coefficient (µ = shear stress/σneff) is relatively low (µ = 0.35-0.45), poorly sensitive to fluid temperature and we observe creep. Instead, for T ≥ 300°C and in the presence of water in vapor state, the µ is higher (= 0.80-0.90) and we observe stick-slip behaviour.
The experimental approach of this study aims to understand the nucleation of earthquakes or of slow slip events along mid ocean ridges and transform faults and to contribute to the assessment of seismic hazard associated with CO2 storage by carbonation of serpentinite in deep reservoirs.
How to cite: Salvadori, L., Di Toro, G., and Tesei, T.: Frictional strength and healing behaviour of natural carbonated serpentinites at hydrothermal conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8673, https://doi.org/10.5194/egusphere-egu25-8673, 2025.
The ability of faults to regain strength between seismic events (frictional healing) is crucial to understand the seismic cycle. In lithologically heterogeneous faults, differences in healing rates among various rock types can lead to the locking of specific fault patches. These locked segments may store significant amounts of elastic strain energy, which can be dynamically released during earthquakes. Anhydrite is a key component of the Triassic Evaporites, the seismogenic layer responsible for destructive earthquakes in Central Italy, e.g. 2016 Mw 6.5 Norcia mainshock. Its complex mechanical behavior, strongly influenced by boundary conditions, remains underexplored. Minor variations in effective pressure, humidity, loading rate, and temperature alter healing properties, rheology, and fault slip behavior of anhydrite. These mechanical characteristics are inherently tied to its elastic properties. Hence, the broad spectrum of mechanical behaviors observed should correspond to an equally wide variation in its elastic moduli.
We performed dry and wet friction experiments on anhydrite gouge using the BRAVA2 biaxial apparatus. These experiments include Slide-Hold-Slide (SHS) sequences to investigate the healing properties of anhydrite by varying temperature between 20 and 100 °C. To inform mechanical data with the microphysical evolution of the fault, we equipped the sample assembly with PZT sensors in transmission mode. These sensors record ultrasonic wave (UW) propagation through the sample during SHS tests. Finally, mechanical and ultrasonic measurements were accompanied by comprehensive microstructural analysis.
At room temperature, distinct mechanical features emerge between dry and wet samples. Wet experiments are characterized by lower friction (μ = 0.49) and higher healing rate (β = 0.015) with respect to dry ones (μ = 0.6 and β = 0.004). In both wet and dry tests fault healing follows a log-linear dependence with hold duration, however, in wet samples this relationship occurs only after a characteristic cut-off time, tc (s). We report a log-linear increase of UW amplitude with hold time. Microstructural analysis of wet samples reveals shear localization and grain size reduction within multiple Y, B, and R shear bands. Conversely, dry samples predominantly feature distributed deformation within R shear bands and local S-C structures.
The observed differences between dry and wet experiments suggest that water-activated processes play a major role in controlling shear strength and healing properties of anhydrite. This hypothesis is corroborated by the presence of a cut-off time for wet healing measurements. We interpret tc as a necessary time for water-activated deformation mechanisms to effectively operate by increasing the healing rate.
The evidence of a log-linear relationship between UW amplitude and hold duration testifies that fault restrengthening is intimately related to gouge porosity reduction and fault zone evolution.
Our approach aims to correlate reductions in shear modulus with shearing along specific slip planes, which are known to be active through microstructural analyses. To achieve this goal, the relationship between complex frictional healing and the elastic properties of anhydrite will be investigated via the extraction of elastic moduli from UW velocities.
How to cite: Mauro, M., Guglielmi, G., De Solda, M., Trippetta, F., Collettini, C., and Scuderi, M.: Dynamics of frictional healing of anhydrite bearing faults imaged by ultrasonic waves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8830, https://doi.org/10.5194/egusphere-egu25-8830, 2025.
Faults are heterogeneous at all scales. Crustal faults extend for tens or hundreds of kilometers across which they intersect many different lithologies. In the fault core, meter-scale blocks are embedded within a shear zone mélange and, at the grain-scale, fault segments comprise patches of weak and strong minerals. This structural heterogeneity may be associated with an heterogeneous stress distribution on-fault and has therefore been invoked to explain observations of different slip behaviours occuring simultaneously and at the same location on individual faults.
Conceptually, the structural and mechanical heterogeneity along fault is often described in terms of rheological asperities that can either be competent, have a velocity-weakening frictional behavior and tend to slip unstably or be less competent, have a velocity-strengthening frictional behaviour and slip stably. To understand the spectrum of slow, intermediate, and fast slips behaviors observed in nature, the laboratory studies have investigated the effect of rheological asperities on fault stability and slip behaviour. Laboratory experiments have been performed using mixtures of gouge materials with different frictional properties mixed homogeneously in various proportions or using spatially heterogeneous gouges with predefined layering perpendicular or parallel to the shear direction. In gouge samples prepared using talc-calcite mixtures, a 20% fraction of talc – the weak phase – was shown to drastically change the frictional properties of calcite gouge. However, recent results for vertically segmented gouges prepared from claystone and sandstone showed that fault friction and its rate-dependence are not simply controlled by the weakest lithology nor by a homogeneous mixture of the juxtaposing lithologies.
We performed friction experiments at room temperature in a servo-controlled biaxial apparatus using homogeneous and heterogeneous gouge samples prepared from calcite and talc minerals in various proportions by weight. Calcite and talc were chosen for their well-known antagonist frictional behaviour, as the strong velocity-weakening lithology and weak velocity-strengthening lithology, respectively. Heterogeneous gouge samples consist of a cylindrical inclusion of talc/calcite embedded within calcite/talc. For each experiment, two identical layers of gouge were placed in between three grooved sliding blocks, in a double-direct shear configuration, and a constant normal stress of 40 MPa was applied. Samples were sheared at a sliding velocity of 10 µm.s-1 until a steady state was reached. Velocity-stepping and slide-hold-slide sequences were then performed, under fully dry conditions.
Overall, we observe that the coefficient of friction decreases with increasing talc content. However, depending on the geometry of the slip interface – a weak inclusion in a stronger and continuous lithology or the opposite – the decrease in strength associated with the presence of phyllosilicate minerals varies non linearly. Velocity weakening during shearing is reduced in the case of a strong calcite inclusion embedded in a weaker talc continuum. Our results show that the rheological heterogeneity associated with the presence of weak or strong inclusions exerts a second order control on the frictional behaviour of our simulated gouges.
How to cite: Carbillet, L., Guérin-Marthe, S., Hofer Apostolidis, K., and Violay, M.: Effect of strong and weak inclusions on the frictional behaviour of fault gouges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16382, https://doi.org/10.5194/egusphere-egu25-16382, 2025.
Experimental observations on fault gouges suggest that shear localization is a prerequisite for the nucleation of instabilities. Synthetic gouges typically produce lab-quakes when the shear deformation is localized along sharp, knife-edge shear planes – a condition that satisfies the steady-state existence requirement of the rate-and-state friction framework. Similarly, exhumed fault cores exhibit shear planes so localized that they appear as mirror surfaces.
Yet, the scenario in nature is far more complex. Many faults contain multiple fault cores, multiple localized shear planes, cemented fault rocks, and evidence for fault core recycling. This suggests that deformation localized along a principal slip plane during an earthquake – unlike in controlled shear experiments – does not necessarily persist over the lifespan of a mature fault. While in laboratory gouge experiments the steady state corresponds to a microstructural fabric that does not evolve significantly over seismic cycles, fault rock fabrics in nature evolve significantly during the seismic cycle—remaining far from a simple localized steady-state fabric.
Here, we present a preliminary study aiming at reconciling these two perspectives: the laboratory-derived nucleation, which involves deviations from a pre-existing steady-state, and the field-derived nucleation, often occurring far away from any steady-state condition. To address this, we conducted double-direct shear experiments on quartz gouges at 30 MPa normal stress, reactivating faults via shear stress steps that allowed spontaneous fault acceleration or deceleration.
The novelty of our approach lies in (1) the different textural states imposed on the gouge before reactivation and (2) the integration of acoustic emissions monitored during fault acceleration with post-mortem microstructures. Specifically, we designed three textures: a pre-localized texture – with localized shear planes developed by prior shearing at constant velocity and normal stress of 30 MPa for a few millimeters; a homogeneous texture – compacted under a normal stress of 30 MPa without prior shearing before reactivation; and an overconsolidated homogeneous texture – compacted under normal stress of 60 MPa before reactivation at 30 MPa.
Preliminary results reveal clear correlations between acoustic emission rate, slip evolution, and the degree of localization in post-mortem microstructures. Pre-localized textures remain locked until a critical stress is reached, after which they abruptly accelerate. Homogeneous textures display slow, progressive acceleration, with increasing slip velocity at higher shear stresses. The overconsolidated texture exhibits intermediate behavior. The acoustic emission signature during low constant-velocity slip reflects the grain interactions typical of granular flow, while rapid acceleration produces impulsive lab-quake-like signals typical of localized rupture nucleation.
These preliminary observations suggest a feedback loop between the localization of deformation and instability growth. While this type of relationship between shear strain localization and slip rate is well-established for the co-seismic propagation phase, our observations indicate that it may play a role during the nucleation phase, challenging the steady-state assumption commonly derived from laboratory studies.
How to cite: Giorgetti, C., Pignalberi, F., Mastella, G., Scuderi, M. M., and Collettini, C.: Slip Localization versus Instability Nucleation Feedback Loop: A Laboratory Perspective from Gouge Deformation Experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18843, https://doi.org/10.5194/egusphere-egu25-18843, 2025.
Recent observations of many large earthquakes suggest a pronounced interaction of seismic sequences and aseismic slip (Kato & Ben-Zion, 2020). Among them, the spatio-temporally clustered seismic sequences may be related to internal stress transfer through event-event triggering processes (Davidsen et al., 2021). These evolving stress correlations at different length scales may be a key component to earthquake nucleation. However, the coupling between aseismic deformation and seismic triggering remains poorly understood due to observational limitations. In this study, we performed a triaxial experiment at 50 MPa confining pressure on a Rotondo granite sample. The sample was pre-notched to induce localized stress concentrations. The deployment of distributed strain sensing (DSS), based on fiber-optic technology, captures the transient behavior of aseismic deformation leading to system-size failure. We show that, at peak stress (σp = 420 MPa), the strain first builds up and accelerates near the edges of notches. During a subsequent small stress drop (Δσd = 1.5 MPa), a sharp contrast between positive and negative strain rates appears. This asymmetric deformation reflects the local stress redistribution associated with the development of shear cracks emanating from the notches. Following this, a transient recovery is observed, as the concentrated strain rate transfers to the surrounding regions. This indicates that the shear crack is growing away from the notches towards the middle of sample. Acoustic emissions (AEs) recorded throughout the failure sequence were analyzed in conjunction with local strain rates, strain gradients, and the speed at which the strain concentrations propagate. This study provides novel insights into the spatio-temporal evolution of shear cracks, revealing the complex interplay between strain localization, aseismic transients, foreshock activity and stress redistribution during the preparatory phase preceding dynamic failure.
References:
Davidsen, J., Goebel, T., Kwiatek, G., Stanchits, S., Baró, J., & Dresen, G. (2021). What Controls the Presence and Characteristics of Aftershocks in Rock Fracture in the Lab? Journal of Geophysical Research: Solid Earth, 126(10), e2021JB022539. https://doi.org/10.1029/2021JB022539
Kato, A., & Ben-Zion, Y. (2020). The generation of large earthquakes. Nature Reviews Earth & Environment, 2(1), 26–39. https://doi.org/10.1038/s43017-020-00108-w
How to cite: Chen, H., Selvadurai, P. A., Michail, S., Salazar Vásquez, A. F., Madonna, C., and Wiemer, S.: Spatio-Temporal Organization of Earthquakes: Insights from Aseismic Transients and Seismic Triggering in Rock Fracture, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8940, https://doi.org/10.5194/egusphere-egu25-8940, 2025.
Natural faults are typically surrounded by a damage zone consisting of fractures of varying scales and geometries, which can significantly influence the dynamics of earthquake ruptures. Numerical studies have shown that damage can affect rupture parameters such as velocity, style, and extent. However, only a limited number of experimental studies have examined the effect of damage on the rupture process, focusing primarily on the rupture speed. Here, we present direct experimental observations on how damage geometry can affect earthquake rupture dynamics on a planar fault. We use polymethyl methacrylate (PMMA) specimens with a pre-cut planar fault and create damage near the fault with varying crack geometry and spacings using laser cutting technology. We generate spontaneously propagating shear ruptures along the main faults and image the rupture using an ultra-high-speed camera operating at one million frames per second. By employing Digital Image Correlation (DIC) techniques, we obtain detailed evolution maps of velocities, displacements, and strains associated with the propagation of the ruptures. Initial results demonstrate that damage zone characteristics can significantly influence the slip velocity, rupture style, and speed, including the transition from sub-Rayleigh to supershear velocities. Such results can offer valuable experimental observations on how damage zones influence earthquake rupture dynamics and deepen the understanding of the complex interplay between fault structures and rupture processes.
How to cite: Ghosh, S. and Tal, Y.: The Effect of Fault Damage Zone on the Dynamics of Earthquake Ruptures: Experimental Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3648, https://doi.org/10.5194/egusphere-egu25-3648, 2025.
Fault geometry is increasingly regarded as a key parameter that affects all aspects of the earthquake cycle, yet the in-situ geometry of active faults remains poorly resolved, and they are often modeled as largely planar. On the other hand, recent advances in sensing and computational abilities enable measuring the co-seismic slip of large earthquakes in high resolution, both on the surface and at seismogenic depths. Previous analytical and numerical studies showed that the slip distribution of an earthquake is mechanically linked to the fault geometry through its curvature, though this link has not yet been verified. Here we show experimental verification of this link, by measuring at high precision the shear slip profiles along non-planar interfaces in laboratory earthquakes. We trigger dynamic shear ruptures that propagate along the interface between two loaded and matching PMMA plates and, using image correlation of ultrahigh-speed photography, resolve the propagating ruptures and the resulting displacements. The plates are pre-cut along a desired geometry, and we compare the slip calculated from the geometry and the experimental shear slip at each pixel along the interface. We show that, as predicted analytically, fault curvature is correlated to slip gradient when the plates are in contact and anti-correlated when there is opening. These relationships are clearly visible in our results at all measured scales regardless of the rupture complexity. Our results suggest that variations of the co-seismic slip along a fault can be highly indicative of the in-situ fault geometry and, alternatively, that slip distribution may be predicted along a fault with known geometry.
How to cite: Gabrieli, T., Romanet, P., Tal, Y., and Schuderi, M. M.: Validating the link between fault geometry and slip distribution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12897, https://doi.org/10.5194/egusphere-egu25-12897, 2025.
The mechanisms that lead a fault in the brittle crust to catastrophically fail during fluid injection remain poorly understood. In traditional rock mechanics, significant effort has been devoted to developing fluid injection experiments that reactivate small specimen surfaces over their whole area. However, in natural settings, only a portion of the fault may initially experience an increase in fluid pressure and reactivation by enlarging the area of slip.
Therefore, it is important to explore further the processes that lead to nucleation on a localized patch subjected to fluid injection to involve a larger portion of the fault that are not initially subjected to the elevated fluid pressure. To do so, we developed a new bi-axial apparatus specifically designed to investigate the nucleation phase of fluid injection-induced earthquakes on large enough sample.
This apparatus accommodates slabs of rock with a sliding surface of 15 x 17 cm and 1 cm thick. It is equipped with two servocontrolled hydraulic rams capable of delivering horizontal and vertical forces up to 450kN. The fluid pressure (both upstream and downstream) and both rams are controlled by adapted Nova-Swiss hand pumps that are independently managed by EUROTHERM process controllers, which operate MAXXON brushless electric motors via ESCON digital servo-controllers. This setup enables precise servo-control of each piston and upstream and downstream pressure in either displacement or pressure mode, using feedback from LVDTs and pressure transducers, respectively.
We designed a new double L-shaped assembly that ensures a uniform shear stress distribution on the sliding surface prior to reactivation, as shown by finite element analysis. The assembly is equipped with eight piezoelectric transducers to record acoustic emissions (AE) and to conduct active velocity surveys, as well as strain and displacement gauges placed across the sliding surface to monitor local strains and finite displacements. The slip surface can be machined to form an area with an initial stress concentration around its tip so that slip can be initiated entirely by raising the fluid pressure in the ‘crack’. The sample material chosen is Pennant sandstone, a tight sandstone with high cohesive strength and very low porosity and permeability.
Here, we present a suite of preliminary experiments ranging from conventional stable/unstable frictional sliding to fluid injection-induced fault reactivation. Acoustic emissions were utilized to monitor the evolution of the seismic b-value and to locate AE events throughout the experiments.
How to cite: Bigaroni, N., Mecklenburgh, J., Chandler, M., Paul, L., and Rutter, E.: BeeAx: A New Biaxial Apparatus to Investigate Shallow Brittle Rock Deformation and Frictional Sliding, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10995, https://doi.org/10.5194/egusphere-egu25-10995, 2025.
Fluid pressure plays a crucial role in controlling fault reactivation in both natural and induced seismicity. The effective normal stress is linearly reduced by an increase in fluid pressure (Pf) with σeff = σn - S · Pf, which lowers the frictional strength of the fault, τ=µ·σeff, increasing the potential for fault reactivation and seismic slip. Upon reactivation, slip can occur quasi-statically or dynamically depending on the interplay between σn and Pf and mediated by the S parameter, (the hydromechanical coupling) and by the rate-and-state properties of the fault materials. In this context, the fault zone structure dictates the frictional properties as well as the fault hydro-mechanical coupling, particularly when S ≠ 1 and reactivation might occur at effective stresses different than predicted.
In Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG, Switzerland), a target fault zone chosen for fluid-induced fault stimulation is characterized by a fractured host rock surrounding a sub-centimetric fault core with fault gouge and bare-rock asperities. Therefore, to define slip mode of the target fault it is important to characterized the frictional properties of both fault gouge and bare-rock asperities taking advantage of a laboratory controlled experimental environment.
Fault stimulation by fluid injection was simulated in laboratory by increasing the Pf following an injection protocol suitable for the BULGG fluid stimulation. Experiments were performed on both the fault gouge sampled from the target fault and on bare rock surfaces sampled in the surrounding host rock. We employed a rotary shear apparatus (SHIVA) to perform fluid injection experiments. First, we imposed the stress conditions measured at depth in the underground laboratory, halved due to apparatus limitations: 7.5 MPa σeff, 7.5 MPa confining pressure and 2.5 MPa Pf. Second, we imposed a slip rate of 10-5 m/s for 0.01 m to develop a stable fault core structure. Third, we applied a constant shear stress of 2.7 MPa, considering the slip tendency measured on the target fault (0.35). We then increased stepwise the Pf by 0.1 MPa every 150 s. After fault slip initiation, the maximum allowed slip velocity was 0.1-1 m/s. Between each of the experimental stages, permeability and transmissivity were measured with the gradient (Darcy) or Pf oscillations methods.
We show that fault reactivation and slip behavior are different between gouge and bare rocks: in gouge creep and dilatancy precede reactivation, whereas in bare rock surfaces reactivation is sudden and not preceded by neither tertiary creep nor dilatancy indicating that dynamic reactivation is promoted in smooth bare-rock surfaces. Moreover, gouge displays a higher friction (0.58 vs 0.49) and a lower hydraulic transmissivity (i.e., 10-19 vs 10-17 m3) than bare rocks.
Here we proceed to test a suite of constitutive models against our data: rate and state friction, (Rudnicki, 2023; Cappa et al., 2022), and a fully coupled poromechanical model (Dal Zilio et al., in prep.), to understand what are the physical processes controlling the onset and style of fault activation in the two fault core structures.
How to cite: Aretusini, S., Cornelio, C., Spagnuolo, E., Volpe, G., Pozzi, G., Dal Zilio, L., Selvadurai, P., and Cocco, M.: Fault core structure and the fault slip behavior during fluid injection: insights from laboratory friction experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7883, https://doi.org/10.5194/egusphere-egu25-7883, 2025.
Compared to other kinds of fluid-related seismicity, reservoir-induced seismicity (RIS) is usually characterized by higher magnitudes. Seismic and water level monitoring and statistical modelling, however, do not provide comprehensive understanding of the RIS mechanism and controls. This study presents a novel finite element method-based 2D poro-visco-elasto-plastic fully dynamic earthquake model, specifically applicable to RIS simulations. In the first stage of the simulations, Drucker-Prager plasticity is used to generate a normal fault in the Earth’s upper crust with enhanced porosity, over a long time-scale of millions of years. In the second stage of the simulations, RIS is modelled under typical reservoir impoundment dynamics, producing four seismic sequences, triggered by pore pressure increase at the fault at shallow depth below the reservoir. This pressurization is released by aftershocks in every seismic cluster, accompanied by permeability hikes at the fault and associated with fault “valving” behaviour. A dynamic coseismic rupture phase driven by wave-mediated stress transfers coupled with rate-and-state dependent friction coefficient weakening is modelled, along with interseismic deformations. Coseismic crack opening in a dilatant regime, inducing porosity and permeability hikes especially emphasized at the fault, is implemented. The model component verifications demonstrate convincing agreement with theoretical predictions. The model allows investigation of spatio-temporal RIS characteristics and their controls. It may contribute to earthquake prediction in situ and facilitate earthquake mitigation policies.
How to cite: Katsman, R. and Ben-Avraham, Z.: A Dynamic Poro-Visco-Elasto-Plastic Earthquake Simulator with Spontaneous Dilatant Coseismic Rupture: Modelling Fault Deformations at Reservoir-Induced Seismicity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5024, https://doi.org/10.5194/egusphere-egu25-5024, 2025.
Flash heating is a critical phenomenon in fault gouges, occurring during rapid slip events that generate temperature surges at the grains or asperity contacts. These abrupt temperature increases trigger mechanisms that weaken the gouge material, reducing its shear strength. This process plays a key role in modulating fault dynamics and can significantly impact the propagation of earthquakes [1, 2]. Although many studies have considered microscale friction of uniform or narrowly graded grain sizes, natural fault zones commonly consist of a wide range of particle sizes [3].
In this work, we used a three-dimensional discrete element framework to simulate shear in a granular fault gouge to replicate the rotary-shear experiment. A local temperature-dependent friction law was implemented in which the friction angle of a grain decreases sharply once its temperature exceeds a specified cut-off threshold [4], quantifying how grain size ranges influence the onset of thermally-activated weakening by varying the PSD of our simulated fault gouge—from monodisperse (all grains have the same size) to highly polydisperse (very broad size ranges)—and determining how this range modulates the onset of flash heat weakening. Our numerical results demonstrate that monodisperse samples distribute contact forces more evenly among grains, and that heating and subsequent weakening occur more synchronously across the sample. This uniform distribution of contact forces and thermal effects results in a drop in the macroscopic friction coefficient in a relatively abrupt way. In contrast, samples with polydisperse particles have a wide range of grain sizes, which can give rise to a heterogeneous stress state and thereby strengthen local frictional heating in some areas of the sample, thus allowing a gradual and disordered decline in the macroscopic friction coefficient. Thus, larger grains in polydisperse assemblies can be considered as stress bridges, sustaining higher values of contact forces; on the other side, small grains have lower thermal capacities (via small masses), and they heat up and soften quicker than larger ones with the same frictional work rate. Such a mixture of these aspects explains a larger percentage of weakened particles in polydisperse assemblies and its lower residual friction compared to samples with narrower PSDs. These results emphasize the importance of considering the natural heterogeneity of grain sizes in models of, and observations of temperature-dependent weakening in fault gouges. The polydispersity degree can have a dramatic impact on the rate and extent to which flash heating can induce a transition from a strong (frictional) resisting to a weakened state. Knowledge of these PSD-dependent processes leads to a more realistic representation of dynamic fault weakening and enhances our understanding of earthquake rupture dynamics at naturally heterogeneous fault zones.
References
[1] J.R. Rice. Journal of Geophysical Research: Solid Earth, 111(5), 2006.
[2] B.P. Proctor, T.M. Mitchell, G. Hirth, D. Goldsby, F. Zorzi, J.D. Platt, and G. Di Toro. Journal of Geophysical Research, Solid Earth, 119(iv):3076–3095, 2014.
[3] C. Marone and C.H. Scholz. Journal of Structural Geology, 11(7):799–814, 1989.
[4] A. Taboada and M. Renouf. Geophysical Journal International, 233(2):1492–1514, 2023.
How to cite: Shahabi, H. and Rattez, H.: The Influence of Particle Size Distributions on Flash Heating and Thermally Induced Weakening in Fault Gouges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21574, https://doi.org/10.5194/egusphere-egu25-21574, 2025.
Posters virtual: Tue, 29 Apr, 14:00–15:45 | vPoster spot 2
EGU25-20105 | ECS | Posters virtual | VPS28
Gravimetric Investigation and Analysis of Tectonic Features and Mineralization Zones in the Central High Atlas (Morocco).Tue, 29 Apr, 14:00–15:45 (CEST) | vP2.3
The Central High Atlas in Morocco is characterized by complex geological structures shaped by tectonic and magmatic processes. Gravimetry, a geophysical technique sensitive to subsurface density variations, plays a crucial role in exploring and understanding these features. This study provides a bibliometric analysis of global research on the application of gravimetry, with a specific focus on its use in the Central High Atlas.
The main objectives of this study are to identify global research trends and applications of gravimetry in the study of geological structures, analyze key contributors, scientific collaborations, and dominant themes in gravimetric research, and compare findings from studies conducted in the Central High Atlas with those from other regions worldwide.
A bibliometric analysis was conducted using data from Scopus and Web of Science databases. Keywords such as "gravimetry," "Central High Atlas," and "geological structure" were employed to extract relevant studies. The analysis utilized the R-bibliometrix package and VOSviewer software to map collaboration networks, visualize thematic clusters, and analyze global research trends over time.
The results reveal a significant increase in gravimetric studies over the last two decades, reflecting growing interest in its applications in mountainous regions like the Central High Atlas. The findings highlight deep-seated geological structures, active fault systems, and the relationship between gravimetric anomalies and tectonic processes. Moreover, a comparative analysis shows that studies in Morocco focus heavily on tectonic and magmatic processes, while research in other countries often emphasizes technological advancements and methodological innovations.
This bibliometric study underscores the importance of gravimetry as a tool for exploring complex geological structures in the Central High Atlas. It also highlights the need for stronger international collaborations and interdisciplinary research to advance gravimetric methodologies and foster knowledge exchange across regions.
How to cite: Assoussi, S., Hahou, Y., Khalifa, M., Saadaoui, F., and Oujane, B.: Gravimetric Investigation and Analysis of Tectonic Features and Mineralization Zones in the Central High Atlas (Morocco)., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20105, https://doi.org/10.5194/egusphere-egu25-20105, 2025.
EGU25-20168 | ECS | Posters virtual | VPS28
Geophysical and Remote Sensing Contributions to Understanding Geological Structures in the Central High Atlas (Morocco): A Review and Analytical Study.Tue, 29 Apr, 14:00–15:45 (CEST) | vP2.4
This study evaluates the contributions of geophysics and remote sensing to structural mapping in the Central High Atlas region of Morocco. A bibliometric analysis was conducted using data collected from databases such as Scopus and Web of Science. Keywords related to geophysics, aeromagnetic, remote sensing, structural mapping, and the Central High Atlas were used to systematically identify relevant research articles. Analytical techniques, including citation analysis, co-authorship analysis, keyword analysis, and network analysis (using VOSviewer), were applied to explore research trends, collaborations, and key focus areas.
The findings highlight notable research trends in the application of geophysics and remote sensing, identifying key contributors, influential institutions, and pivotal publications in this domain. Research gaps and opportunities for further investigation were also uncovered. Visualization of research networks provided insights into collaboration patterns and thematic focus areas.
This study underscores the importance of geophysics and remote sensing in enhancing the understanding of the Central High Atlas's structural geology. It offers a foundation for future research, emphasizing the need for interdisciplinary collaboration and advanced methodologies to address existing research gaps and further explore the region's geological complexities.
How to cite: Saadaoui, F., Hahou, Y., Ousaid, L., Assoussi, S., and Oujane, B.: Geophysical and Remote Sensing Contributions to Understanding Geological Structures in the Central High Atlas (Morocco): A Review and Analytical Study., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20168, https://doi.org/10.5194/egusphere-egu25-20168, 2025.
