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  • 1
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    Effect of water on the frictional behavior of cohesive rocks during earthquakes (2015)
    Geological Society of America
    Details
    Publication Date: 2021-12-16
    Description: Fluid-rock interactions can control earthquake nucleation and the evolution of earthquake sequences. Experimental studies of fault frictional properties in the presence of fl uid can provide unique insights into these interactions. We report the fi rst results from experiments performed on cohesive silicate-bearing rocks (microgabbro) in the presence of pressurized pore fl uids (H2 O, drained conditions) at realistic seismic deformation conditions. The experimental data are compared with those recently obtained from carbonate-bearing rocks (Carrara marble). Contrary to theoretical arguments, and consistent with the interpretation of some fi eld observations, we show that frictional melting of a microgabbro develops in the presence of water. In microgabbro, the initial weakening mechanism (fl ash melting of the asperities) is delayed in the presence of water; conversely, in calcite marble the weakening mechanism (brittle failure of the asperities) is favored. This opposite behavior highlights the importance of host-rock composition in controlling dynamic (frictional) weakening in the presence of water: cohesive carbonate-bearing rocks are more prone to slip in the presence of water, whereas the presence of water might delay or inhibit the rupture nucleation and propagation in cohesive silicate-bearing rocks.
    Description: Published
    Description: 27-30
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: reserved
    Keywords: carbonates faults ; hydro-elasto-dynamics ; earthquake nucleation ; friction ; rock mechanics ; fluid-rcok interactions ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems ; 04. Solid Earth::04.01. Earth Interior::04.01.04. Mineral physics and properties of rocks ; 04. Solid Earth::04.01. Earth Interior::04.01.05. Rheology ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Pore fluid in experimental calcite-bearing faults: Abrupt weakening and geochemical signature of co-seismic processes (2012)
    Elsevier Science Limited
    Details
    Publication Date: 2021-12-16
    Description: While itiswidelyrecognizedthatfluidsinfluencefaultstrengthandearthquakenucleation,propaga- tion andarrest,theireffectsonco-seismicslidingfrictionareonlyconjectured.Toshedlightonthese effects,55highvelocity(41 m s 1) frictionexperimentswereconductedatroomtemperatureon Carraramarblesamplesinthepresenceofporefluid(upto15MPaporepressure),room-humidityand ‘‘vacuum’’(10 4 mbar)conditions.Inalltheexperiments,thefrictioncoefficientevolvedfromapeak value of0.6–0.8toasteady-statevalueof0.1inabout1–1.5mofslip.However,experiments performedinthepresenceofporefluidhadalargeandmoreabruptdecreaseinfrictionatthe initiationofsliding(65%after20mmofslip),whereasexperimentsperformedundervacuumandroom humidityconditionsshowedinitialvelocity-strengtheningbehaviorfollowedbyamoregradual reductioninfriction.Thisindicatesthatcalcite-bearingrocksaremorepronetoslipinthepresence of water.Underroom-humidityconditions,CO2 was detectedduringtheentiredurationofthe experiment.Inthepresenceofporefluid,HCO3 and Ca2þ were detectedforslips 40.1 m.Thelack of decarbonationproducts(HCO3 and Ca2þ) inporefluidexperimentsforslip o0.1 mimpliesthat the abruptweakeningisnotrelatedtodecarbonation(orthattheabundanceofthereactionproductsis below theresolutionoftheanalyticalmethods).Giventhemodestthermalexpansionofwater, the estimatedthermalpressurizationduringtheabruptweakeningappearstobenegligible.Instead, we suggestthatabruptweakeningisduetosubcriticalcrack-growth,hydrolyticweakeningandbrittle failureoftheasperitiesontheslidingsurfaces.Modelingshowsthattheoccurrenceinnatureof co-seismic(water-present)decarbonationreactionssimilartothosetriggeredinthelaboratorycould yield sufficientreactionproducttobedetectedinaquiferslocatedintheproximityofactivefaults.
    Description: Published
    Description: 74-84
    Description: JCR Journal
    Description: restricted
    Keywords: earthquakes friction pore fluid carbonate-bearing rocks ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Effect of glass on the frictional behavior of basalts at seismic slip rates (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-12-16
    Description: We performed 31 friction experiments on glassy basalts (GB) and glass-free basalts (GFB) at slip rates up to 6.5 m s−1 and normal stress up to 40 MPa (seismic conditions). Frictional weakening was associated to bulk frictional melting and lubrication. The weakening distance (Dw) was about 3 times shorter in GB than in GFB, but the steady state friction was systematically higher in GB than in GFB. The shorter Dw in GB may be explained by the thermal softening occurring at the glass transition temperature (Tg ~500°C), which is lower than the bulk melting temperature (Tm ~1250°C) of GFB. Postexperiment microanalyses suggest that the larger crystal fraction measured in GB melts results in the higher steady state friction value compared to the GFB melts. The effect of interstitial glass is to facilitate frictional instability and rupture propagation in GB with respect to GFB.
    Description: Published
    Description: 348-355
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: embargoed_20160201
    Keywords: Earthquakes ; Friction ; Basalts ; Interstitial glass ; 04. Solid Earth::04.01. Earth Interior::04.01.04. Mineral physics and properties of rocks ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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