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  • 1
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    Strength evolution of simulated carbonate-bearing faults: The role of normal stress and slip velocity (2018)
    Elsevier
    Details
    Publication Date: 2018-04-01
    Print ISSN: 0191-8141
    Electronic ISSN: 1873-1201
    Topics: Geosciences
    Published by Elsevier
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    PAPER CURRENT
  • 2
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    Stabilization of fault slip by fluid injection in the laboratory and in situ (2019)
    American Association for the Advancement of Science
    Details
    Publication Date: 2019-03-20
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science
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    PAPER CURRENT
  • 3
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    Mechanical data of simulated basalt-built faults from rotary shear and direct shear experiments (2021)
    GFZ Data Services
    Details
    Publication Date: 2022-02-11
    Description: Abstract
    Description: Here we report the raw data of the friction experiments carried out on basalt-built simulated faults defined by rock-on-rock contacts and powdered gouge. The experiments were specifically designed to investigate the role of fault microstructure on the frictional properties of basalts and the fault slip stability, and were conducted with the rotary-shear apparatus (SHIVA) and the biaxial deformation apparatus (BRAVA), hosted at the National Institute of Geophysics and Volcanology (INGV) in Rome. Simulated faults were sheared at constant normal stress from 4 to 30 MPa. In SHIVA experiments, we deformed samples at constant slip velocity of 10 μm/s up to 56 mm net slip. In BRAVA tests we performed a sequence of velocity steps (0.1 to 300 μm/s), followed by slide-hold-slide tests (30-3000 s holds; V=10 μm/s slides). Our main results highlight the frictionally strong nature of basalt faults and show opposite friction velocity dependence upon the velocity upsteps: while fault gouges exhibit velocity weakening behavior with increasing normal stress and sliding velocity, bare rock surfaces transition to velocity strengthening behavior as we approach higher slip velocities. The experiments setup and data are further described in the manuscript “Frictional properties of basalt experimental faults and implications for volcano-tectonic settings and geo-energy sites” to which these data are supplementary material.
    Keywords: Fault mechanics ; Friction of basalts ; Rate and State Friction ; Bare rock surfaces ; Simulated fault gouge ; EPOS ; multi-scale laboratories ; rock and melt physical properties ; alkali-olivine_basalt ; Biaxial ; Friction ; Rotary Shear ; Strain gauge
    Type: Dataset , Dataset
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    DATA GFZ
  • 4
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    The Role of Shear Fabric in Controlling Breakdown Processes During Laboratory Slow‐Slip Events (2021)
    Wiley Agu
    Details
    Publication Date: 2021-05-12
    Description: Understanding the physical mechanisms at the origin of slow‐slip events has been proven a very challenging task. In particular, little is known on the role of fault heterogeneity during slow slip. In this study, we provide evidences that fault fabric controls slip velocity time histories during slow‐slip events generated in the laboratory. We performed experiments using a double‐direct biaxial shear apparatus and two different fault gouges, homogeneous quartz powder, and heterogeneous anhydrite/dolomite mixture. We measure details of fault slip to resolve the slip velocity function and volumetric deformation that, coupled with an analysis of the resulting microstructure, allow us to infer the mechanical processes at play. Our results show that slow‐slip events can be generated for both fault gouges when k ~ kc with similar values of breakdown work. The shear fabric exerts a strong influence during the coseismic breakdown stage. In quartz, where most of the slip occurs on a very localized slipping surface, the peak slip velocity is attained near the final stage of friction breakdown and therefore a relevant amount of the mechanical work is absorbed during slip acceleration. In anhydrite/dolomite mixture, the peak slip velocity is suddenly reached after a relatively small drop in friction, accompanied by fault dilation, implying that most of the mechanical work is absorbed during slip deceleration. For anhydrite/dolomite mixture these results are likely related to heterogeneous slip distribution along the observed foliation. Taken together, these observations suggest that the mechanics of slow‐slip events depends on shear zone fabric.
    Description: Sapienza Grant Ateneo 2018 to C. C. and Horizon 2020 innovation program under the Marie Sklodowska‐Curie 656676 FEAT to M. M. S.
    Description: Published
    Description: e2020JB020405
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Earthquake ; Friction ; Earthquake physics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Slow-to-fast transition of giant creeping rockslides modulated by undrained loading in basal shear zones (2021)
    Nature P. G.
    Details
    Publication Date: 2021-05-12
    Description: Giant rockslides are widespread and sensitive to hydrological forcing, especially in climate change scenarios. They creep slowly for centuries and then can fail catastrophically posing major threats to society. However, the mechanisms regulating the slow-to-fast transition toward their catastrophic collapse remain elusive. We couple laboratory experiments on natural rockslide shear zone material and in situ observations to provide a scale-independent demonstration that short-term pore fluid pressure variations originate a full spectrum of creep styles, modulated by slip-induced undrained conditions. Shear zones respond to pore pressure increments by impulsive acceleration and dilatancy, causing spontaneous decel- eration followed by sustained steady-rate creep. Increasing pore pressure results in high creep rates and eventual collapse. Laboratory experiments quantitatively capture the in situ behavior of giant rockslides and lay physically-based foundations to understand the collapse of giant rockslides.
    Description: ERC grant Nr. 259256 “GLASS”
    Description: Published
    Description: 1352
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: friction ; fluids ; Mechanics of the sliding surfaces
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Frictional Strengthening Explored During Non‐Steady State Shearing: Implications for Fault Stability and Slip Event Recurrence Time (2021)
    Wiley Agu
    Details
    Publication Date: 2021-05-12
    Description: On natural faults that host repeating slip events, the inter‐event loading time is quite large compared to the slip event duration. Since most friction studies focus on steady‐state frictional behavior, the fault loading phase is not typically examined. Here, we employ a method specifically designed to evaluate fault strength evolution during active loading, under shear driving rates as low as 10−10 m/s, on natural fault gouge samples from the Waikukupa Thrust in southern New Zealand. These tests reveal that in the early stages of loading following a slip event, there is a period of increased stability, which fades with accumulated slip. In the framework of rate‐ and state‐dependent friction laws, this temporary stable phase exists as long as slip is less than the critical slip distance and the elapsed time is less than the value of the state variable at steady state. These observations indicate a minimum earthquake recurrence time, which depends on the field value of the critical slip distance and the background slip rate. We compare estimates of minimum earthquake recurrence times with the recurrence times of repeating large earthquakes on the Alpine Fault in southern New Zealand and repeating small‐magnitude earthquakes on the San Andreas Fault system in California. We find that the observed recurrence times are mostly longer than the predicted minimum values, and exceptions in the San Andreas system may be explained by elevated slip rates due to larger earthquakes in this region.
    Description: Deutsche Forschungsgemeinschaft via MARUM Research Centre/Cluster of Excellence (grants FZT15, EXC309, and IK 107/3‐1) and from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement 714430) to M. I.
    Description: Published
    Description: e2020JB020015
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Friction ; Fault ; Earthquake physics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Do scaly clays control seismicity on faulted shale rocks? (2019)
    Details
    Publication Date: 2019-03-29
    Description: One of the major challenges regarding the disposal of radioactive waste in geological formations is to ensure isolation of radioactive contamination from the environment and the population. Shales are suitable candidates as geological barriers. However, the presence of tectonic faults within clay formations put the long-term safety of geological repositories into question. In this study, we carry out frictional experiments on intact samples of Opalinus Clay, i.e. the host rock for nuclear waste storage in Switzerland. We report experimental evidence suggesting that scaly clays form at low normal stress (≤20MPa), at sub-seismic velocities (≤300μm/s) and is related to pre-existing bedding planes with an ongoing process where frictional sliding is the controlling deformation mechanism. We have found that scaly clays show a velocity-weakening and -strengthening behaviour, low frictional strength, and poor re-strengthening over time, conditions required to allow the potential nucleation and propagation of earthquakes within the scaly clays portion of the formation. The strong similarities between the microstructures of natural and experimental scaly clays suggest important implications for the slip behaviour of shallow faults in shales. If natural and anthropogenic perturbations modify the stress conditions of the fault zone, earthquakes might have the potential to nucleate within zones of scaly clays controlling the seismicity of the clay-rich tectonic system, thus, potentially compromising the long-term safeness of geological repositories situated in shales.
    Description: Published
    Description: 59-67
    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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  • 8
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    Fluid Injection and the Mechanics of Frictional Stability of Shale-Bearing Faults (2019)
    Details
    Publication Date: 2019-03-29
    Description: Fluid overpressure is one of the primary mechanisms for triggering tectonic fault slip and human-induced seismicity. This mechanism is appealing because fluid overpressure reduces the effective normal stress, hence favoring fault reactivation. However, upon fault reactivation models of earthquake nucleation suggest that increased fluid pressure should favor stable sliding rather than dynamic failure. Here we describe laboratory experiments on shale fault gouge, conducted in the double direct shear configuration in a true-triaxial machine. To characterize frictional stability and hydrological properties we performed three types of experiments: (1) stable sliding shear experiments to determine the material failure envelope and permeability, (2) velocity step experiments to determine the rate-and-state frictional properties, and (3) creep experiments to study fault slip evolution with increasing pore fluid pressure. The shale gouge shows low frictional strength, μ = 0.28, and permeability, k ~ 10 19 m2 together with a velocity strengthening behavior indicative of aseismic slip. During fault pressurization, we document that upon failure slip velocity remains slow (i.e., v ~ 200 μm/s), not approaching dynamic slip rates. We relate this fault slip behavior to the interplay between the fault weakening induced by fluid pressurization, the strong rate-strengthening behavior of shales, and the evolution of fault zone structure. Our data show that fault rheology and fault stability is controlled by the coupling between fluid pressure and rate-and-state friction parameters.
    Description: Published
    Description: 8364-8384
    Description: 2TR. Ricostruzione e modellazione della struttura crostale
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
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    Experimental Insights Into Fault Reactivation in Gouge‐Filled Fault Zones (2020)
    Details
    Publication Date: 2020-03-10
    Description: Faults in the brittle crust constitute preexisting weakness zones that can be reactivateddepending on their friction, orientation within the local stressfield, and stressfield magnitude.Analytical approaches to evaluate the potential for fault reactivation are generally based on theassumption that faults are ideal planes characterized by zero thickness and constant friction. However,natural faults are complex structures that typically host thick fault rocks. Here we experimentallyinvestigate the reactivation of gouge‐bearing faults and compare the resulting data with theoreticalpredictions based on analytical models. We simulate preexisting faults by conducting triaxial experimentson sandstone cylinders containing saw‐cutsfilled with a clay‐rich gouge and oriented at different angles,from 30° to 80°, to the maximum principal stress. Our results show the reactivation of preexistingfaults when oriented at 30°, 40°, and 50° to the maximum principal stress and the formation of a newfracture for fault orientations higher than 50°. Although these observations are consistent with the faultlock‐up predicted by analytical models, the differential stress required for reactivation strongly differsfrom theoretical predictions. In particular, unfavorable oriented faults appear systematically weaker,especially when a thick gouge layer is present. We infer that the observed weakness relates to the rotationof the stressfield within the gouge layer during the documented distributed deformation that precedesunstable fault reactivation. Thus, the assumption of zero‐thickness planar fault provides only an upperbound to the stress required for reactivation of misoriented faults, which might result in misleadingpredictions of fault reactivation.
    Description: Published
    Description: 4189–4204
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
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    Stabilization of fault slip by fluid injection in the laboratory and in situ (2020)
    Details
    Publication Date: 2020-03-10
    Description: Faults can slip seismically or aseismically depending on their hydromechanical properties, which can be measured in the laboratory. Here, we demonstrate that fault slip induced by fluid injection in a natural fault at the decametric scale is quantitatively consistent with fault slip and frictional properties measured in the laboratory. The increase in fluid pressure first induces accelerating aseismic creep and fault opening. As the fluid pressure increases further, friction becomes mainly rate strengthening, favoring aseismic slip. Our study reveals how coupling between fault slip and fluid flow promotes stable fault creep during fluid injection. Seismicity is most probably triggered indirectly by the fluid injection due to loading of nonpressurized fault patches by aseismic creep.
    Description: Published
    Description: eaau4065
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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