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  • 2020-2024  (8)
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  • 1
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    Effect of Fluid Viscosity on Fault Reactivation and Coseismic Weakening (2020)
    Details
    Publication Date: 2023-11-21
    Description: High‐viscosity fluids are often used during hydraulic fracking operations in georeservoirs. Here we performed dedicated experiments to study the influence of fluid viscosity on fault reactivation and associated induced earthquakes. Experiments were conducted in the rotary‐shear machine Slow to HIgh Velocity Apparatus on experimental fault of Westerly granite saturated by fluids with increasing viscosity (at room temperature) from 0.1 mPa s (water) to 1.2 Pa s (99% glycerol). Fault reactivation was triggered at constant effective normal stress by increasing the shear stress acting on the fault. Our results showed that independent of the viscosity, fault reactivation followed a Coulomb‐failure criterion. Instead, fluid viscosity affected the fault weakening mechanism: flash heating was the dominant weakening mechanism in room humidity and water‐saturated conditions, whereas the presence of more viscous fluids favored the activation of elasto‐hydrodynamic lubrication. Independent of the weakening mechanism, the breakdown work Wb dissipated during seismic faulting increased with slip U following a power law (Wb ∝ U 1.25) in agreement with seismological estimates of natural and induced earthquakes.
    Description: Published
    Description: e2019JB018883
    Description: 3T. Sorgente sismica
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Determination of parameters characteristic of dynamic weakening mechanisms during coseismic slip (2023)
    Wiley-AGU
    Details
    Publication Date: 2023-02-01
    Description: While sliding at seismic slip-rates of ∼1 m/s, natural faults undergo an abrupt decrease of shear stress called dynamic weakening. Asperity-scale (〈〈mm) processes related to flash heating and weakening and, meso-scale (mm-cm) processes involving shear across the bulk slip-zone, related to frictional melting or viscous flow of minerals, have been invoked to explain pronounced velocity-dependent weakening. Here we present a compilation of ∼100 experiments performed with two rotary shear apparatuses. Cohesive rock cylinders of basalt, gabbro, granitoid rocks and calcitic marble were sheared at various values of effective normal stress (σneff = 5–40 MPa), target slip-rate (Vt = 0.1–6.5 m/s) and fluid pressure (Pf = 0–15 MPa). To account for the uncertainties of constitutive parameters, we introduce a norm-based optimization procedure on a set of model parameters by comparing the shear stress evolution inferred from the proposed weakening models with the shear stress measured during the experiments. We analyze the fit to experimental data of each weakening model and we discuss a composite model in which two weakening mechanisms (namely flash heating and bulk melting, flash heating and dislocation/diffusion creep) are used to test the hypothesis that they match the shear stress evolution in different slip ranges. We found that for slip smaller than a slip-switch distance δ0, the weakening is better described by mechanisms occurring at the asperity scale whereas for larger slip values the bulk model performs better. The inferred δ0 values decrease with normal stress suggesting that during earthquakes bulk mechanisms can govern shear stress evolution after a few centimeters of slip.
    Description: Published
    Description: e2022JB024356
    Description: 3T. Fisica dei terremoti e Sorgente Sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Frictional Properties of the Longmenshan Fault Belt Gouges From WFSD‐3 and Implications for Earthquake Rupture Propagation (2023)
    Wiley-AGU
    Details
    Publication Date: 2023-02-09
    Description: The 2008 Mw 7.9 Wenchuan earthquake generated ∼270 and ∼80 km long surface ruptures along the Longmenshan fault belt, namely the Yingxiu-Beichuan fault (YBF) and the Guanxian-Anxian faults (GAF), respectively. So far, most of the frictional investigations were performed on the YBF gouge materials. Here, we present the results of rotary shear friction experiments performed on the GAF gouges recovered from the depth of ∼1.25 km of the Wenchuan Earthquake Fault Scientific Drilling project-3 along the GAF. The fault gouges, mainly composed of quartz, illite, chlorite, and kaolinite, were sheared at slip velocities V ranging from 10−5 to 2 m/s and normal stresses from 8.5 to 10 MPa under both room humidity and wet conditions. At any imposed slip velocity, the wet gouges have an apparent friction coefficient lower than the room humidity one. In addition, enhanced velocity-strengthening behavior at intermediate velocities (10 −2 m/s 〈 V ≤ 10 −1 m/s) was recognized. We characterized the products using field-emission scanning electron microscopy combined with synchrotron X-ray diffraction analysis. These microanalytical investigations evidence the formation of size reduced particles (without mineral phase changes) and R- and Y-shears in the principal slip zone (PSZ). Regardless of the ambient conditions, the width of PSZ was proportional to the input frictional work density (the product of shear stress times displacement). Our results support the hypothesis that the GAF preferentially ruptures through wet fault gouges; however, the enhanced velocity-strengthening regime at intermediate velocities may act as a barrier to slip acceleration during fault rupture propagation.
    Description: This research was financially supported by: (1) the National Natural Science Foundation of China (41830217) (2) the Taiwan ROC (Republic of China) Ministry of Science and Technology (MOST 110-2116-M-008-002-MY2) and Earthquake-Disaster & Risk Evaluation and Management Center (E-DREaM) (3) The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE), Taiwan, (4) ERC CoG 614705 project NOFEAR
    Description: Published
    Description: e2022JB024081
    Description: 3T. Fisica dei terremoti e Sorgente Sismica
    Description: JCR Journal
    Keywords: Friciton, Faults, Longmenshan ; 04.07. Tectonophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Melting of fault gouge at shallow depth during the 2008 MW 7.9 Wenchuan earthquake, China (2024)
    GSA
    Details
    Publication Date: 2024-03-20
    Description: Typical rocks at shallow depths of seismogenic faults are fluid-rich gouges. During earthquakes, on-fault frictional heating may trigger thermal pressurization and dynamic fault weakening. We show that frictional melting, rather than thermal pressurization, occurred at shallow depths during the 2008 MW 7.9 Wenchuan earthquake, China. One year after the Wenchuan earthquake, we found an ~2-mm-thick, glass-bearing pseudotachylyte (solidified frictional melt) in the fault gouges retrieved at 732.6 m depth from the first borehole of the Wenchuan Earthquake Fault Scientific Drilling Project. The matrix of pseudotachylyte is enriched in barium and cut by barite-bearing veins, which provide evidence of co- and postseismic fluid percolation. Because pseudotachylyte can be rapidly altered in the presence of percolating fluids, its preservation suggests that gouge melting occurred in a recent large earthquake, possibly the Wenchuan earthquake. Rock friction experiments on fluid-rich fault gouges deformed at conditions expected for seismic slip at borehole depths showed the generation of pseudotachylytes. This result, along with the presence of a second slip zone attributed to the Wenchuan earthquake at 589.2 m depth, implies that during large earthquakes, frictional melting can occur at shallow depths and that seismic slip can be accommodated by multiple faults. This conclusion is consistent with the evidence from surface faulting that multiple ruptures propagated during the Wenchuan earthquake.
    Description: Published
    Description: 345–350
    Description: OST3 Vicino alla faglia
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Rock deformation vs. radon emission: some constraints from shear stress-controlled experiments (2024)
    Nature PG
    Details
    Publication Date: 2024-04-10
    Description: Numerous field and laboratory studies have been conducted to investigate the relationship between radon variation and seismic events, as well as the complex link between radon emission and rock deformation mechanisms. However, a clear understanding of this correspondence and systematic observations of these phenomena are still lacking, and recent experimental studies have yet to yield conclusive results. In this study, we investigate the possible relationships between radon migration dynamics and rock deformation at the micro-scale through laboratory experiments using the SHIVA apparatus under shear stress-controlled conditions and simultaneous high-resolution radon measurements. We studied the behaviour of three different lithologies to show that radon emission varies in response to rock deformation and this variation is highly dependent on the mineralogy and microstructure. This study represents the first attempt to define radon gas as an indicator of transient and rapid rock deformation at the micro-scale.
    Description: Published
    Description: 16399
    Description: OST4 Descrizione in tempo reale del terremoto, del maremoto, loro predicibilità e impatto
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Friction during earthquakes: 25 years of experimental studies (2024)
    Details
    Publication Date: 2024-04-11
    Description: Dynamic fault strength τ (rock friction in the broad sense) and its evolution with seismic slip and slip rate are among the most relevant parameters in earthquake mechanics. Given the large slip rate (1 m s−1 on average), displacement (up to tens of meters), effective stress (tens of MPa), typical of seismic faulting at depth, thermo-mechanical effects become outstanding: dynamic fault strength is severely affected by fluid and rock phase changes, extreme grain size reduction, and the production of amorphous and unstable materials in the slipping zone. Here, first we will summarize the most relevant findings about dynamic fault strength during seismic slip mainly obtained thanks to the exploitation of dedicated experimental machines (i.e., rotary shear apparatus). However, the interpretation of this experimental dataset remains debated because of technical limitations which impede us to measure fundamental parameters such as temperature, strain rate, pore fluid pressure and grain size in the slipping zone. Without a sound estimate of these physical parameters, any constitutive law proposed to describe the evolution of dynamic fault strength during simulated seismic slip remains speculative. Then, we will discuss the results of some recent experiments which exploit new technical approaches to overcome the main limitations of the previous studies. The experimental approach, together with field studies of the geometry and architecture of exhumed faults and modelling, remains our most powerful tool to investigate seismic-related deformation mechanisms in both natural and human-induced earthquakes.
    Description: Unpublished
    Description: ISRM Regional Symposium - 11th Asian Rock Mechanics Symposium October 21–25, 2021 Beijing, China
    Description: OST3 Vicino alla faglia
    Keywords: earthquakes ; rock mechanics ; structural geology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 7
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    Laboratory simulation of fault reactivation by fluid injection and implications for induced seismicity at the BedrettoLab, Swiss Alps (2024)
    Elsevier
    Details
    Publication Date: 2024-04-11
    Description: Fluid induced fault reactivation experiments will take place as part of the “Fault Activation and Earthquake Rupture” project (FEAR) at the BedrettoLab, an underground laboratory for geosciences and geo-energy excavated within the Rotondo massif (Swiss Alps). The aim of this publication is to characterize frictional properties and permeability of the main segment of the fault zone selected for limited fluid-induced fault reactivation experiments. Firstly, we characterized fault zone microstructures in the field and in thin sections. Secondly, we assessed fault gouge mineralogy by X-ray powder diffraction analysis, yielding a composition in agreement with similar fault gouges in the same area. Finally, we performed a detailed frictional and permeability characterization in laboratory, using BRAVA (Brittle Rock deformAtion Versatile Apparatus). We performed five frictional experiments, run at the actual in-situ conditions: four experiments for frictional properties characterization; and one further experiment where we stimulated the experimental fault by fluid pressurization applying a similar injection protocol designed for the in-situ hydraulic stimulation experiment. Additionally, we performed microstructural analysis on experimental samples to link frictional and permeability properties with fault fabric evolution. The integration of experimental results with field investigations suggests that the selected fault is potentially seismogenic and can be dynamically reactivated and controlled with hydraulic stimulation. This study highlights the importance of bridging the gap between laboratory and in-situ fault characterization, where experimental results become instrumental for the correct design of injection protocols such as those of FEAR project.
    Description: Published
    Description: 229987
    Description: OST3 Vicino alla faglia
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Fracture Energy and Breakdown Work During Earthquakes (2024)
    Annual Review
    Details
    Publication Date: 2024-03-19
    Description: Large seismogenic faults consist of approximately meter-thick fault cores surrounded by hundreds-of-meters-thick damage zones. Earthquakes are generated by rupture propagation and slip within fault cores and dissipate the stored elastic strain energy in fracture and frictional processes in the fault zone and in radiated seismic waves. Understanding this energy partitioning is fundamental in earthquake mechanics to explain fault dynamic weakening and causative rupture processes operating over different spatial and temporal scales. The energy dissipated in the earthquake rupture propagation along a fault is called fracture energy or breakdown work. Here we review fracture energy estimates from seismological, modeling, geological, and experimental studies and show that fracture energy scales with fault slip. We conclude that although material-dependent constant fracture energies are important at the microscale for fracturing grains of the fault zone, they are negligible with respect to the macroscale processes governing rupture propagation on natural faults.
    Description: Published
    Description: 217-252
    Description: OST3 Vicino alla faglia
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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