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  • 1
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    Fault weakening due to CO2 degassing in the Northern Apennines: short- and long-term processes (2008)
    Geological Society of London
    Details
    Publication Date: 2017-04-04
    Description: The influx of fluids into fault zones can trigger two main types of weakening process that operate over different timescales and facilitate fault movement and earthquake nucleation. Short- and long-term weakening mechanisms along faults require a continuous fluid supply near the base of the brittle crust, a condition satisfied in the extended/extending area of the Northern Apennines of Italy. Here carbon mass balance calculations, coupling aquifer geochemistry to isotopic and hydrological data, define the presence of a large flux (c. 12 160 t/day) of deep-seated CO2 centred in the extended sector of the area. In the currently active extending area, CO2 fluid overpressures at 85% of the lithostatic load have been documented in two deep (4–5 km) boreholes. In the long-term, field studies on an exhumed regional low-angle normal fault show that, during the entire fault history, fluids reacted with fine-grained cataclasites in the fault core to produce aggregates of weak, phyllosilicate-rich fault rocks that deform by fluid assisted frictional–viscous creep at sub-Byerlee friction values (m , 0.3). In the short term, fluids can be stored in structural traps, such as beneath mature faults, and stratigraphical traps such as Triassic evaporites. Both examples preserve evidence for multiple episodes of hydrofracturing induced by short-term cycles of fluid pressure build-up and release. Geochemical data on the regional-scale CO2 degassing process can therefore be related to field observations on fluid rock interactions to provide new insights into the deformation processes responsible for active seismicity in the Northern Apennines
    Description: Published
    Description: 175-194
    Description: 4.5. Degassamento naturale
    Description: N/A or not JCR
    Description: reserved
    Keywords: CO2 degassing ; Northern Apennines ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases ; 04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Fault lubrication during earthquakes (2012)
    Details
    Publication Date: 2017-04-04
    Description: The determination of rock friction at seismic slip rates (about 1 m s(-1)) is of paramount importance in earthquake mechanics, as fault friction controls the stress drop, the mechanical work and the frictional heat generated during slip(1). Given the difficulty in determining friction by seismological methods(1), elucidating constraints are derived from experimental studies(2-9). Here we review a large set of published and unpublished experiments (similar to 300) performed in rotary shear apparatus at slip rates of 0.1-2.6 ms(-1). The experiments indicate a significant decrease in friction (of up to one order of magnitude), which we term fault lubrication, both for cohesive (silicate-built(4-6), quartz-built(3) and carbonate-built(7,8)) rocks and non-cohesive rocks (clay-rich(9), anhydrite, gypsum and dolomite(10) gouges) typical of crustal seismogenic sources. The available mechanical work and the associated temperature rise in the slipping zone trigger(11,12) a number of physicochemical processes (gelification, decarbonation and dehydration reactions, melting and so on) whose products are responsible for fault lubrication. The similarity between (1) experimental and natural fault products and (2) mechanical work measures resulting from these laboratory experiments and seismological estimates(13,14) suggests that it is reasonable to extrapolate experimental data to conditions typical of earthquake nucleation depths (7-15 km). It seems that faults are lubricated during earthquakes, irrespective of the fault rock composition and of the specific weakening mechanism involved.
    Description: European Research Counsel
    Description: Published
    Description: 494-498
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: friction ; faults ; lubrication ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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