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Ferri, Fabio
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- PublicationRestrictedFault lubrication during earthquakes(2011-03-24)
; ; ; ; ; ; ; ; ; ;Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Han, R.; Korea Inst Geosci & Mineral Resources, Taejon 305350, South Korea ;Hirose, T.; JAMSTEC, Kochi Inst Core Sample Res, Kochi 7838502, Japan ;De Paola, N.; Univ Durham, Dept Earth Sci, Durham DH1 3LE, England ;Nielsen, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Mizoguchi, K.; Cent Res Inst Elect Power Ind, Civil Engn Res Lab, Chiba 2701194, Japan ;Ferri, F.; Univ Padua, Dipartimento Geosci, I-35131 Padua, Italy ;Cocco, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Shimamoto, T.; China Earthquake Adm, Inst Geol, Beijing 100029, Peoples R China; ; ; ; ; ; ; ; 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 Here we review a large set of published and unpublished experiments (similar to 300) performed in rotary shear apparatus at slip rates of 0.1-2.6 ms(-1).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.253 47 - PublicationRestrictedLow- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy(2011)
; ; ; ; ; ; ; ; ;Ferri, F.; Univ. di Padove, Dpt. Geoscienze ;Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Han, R.; Korea Institute of Geoscience and Mineral Resources, Daejeon, South Korea ;Noda, H.; Seismological Laboratory, California Institute of Technology, Pasadena, California, USA ;Shimamoto, T.; State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing, China ;Quaresimin, M.; Dipartimento di Ingegneria dei Sistemi Industriali, Università degli Studi di Padova, Padua, Italy ;De Rossi, N.; Dipartimento di Ingegneria dei Sistemi Industriali, Università degli Studi di Padova, Padua, Italy ;Hirose, T.; Kochi Institute for Core Sample Research, JAMSTEC, Kochi, Japan; ; ; ; ; ; ; The final slip of about 450 m at about 30 m/s of the 1963 Vaiont landslide (Italy) was preceded by >3 year long creeping phase which was localized in centimeter-thick clay-rich layers (60–70% smectites, 20–30% calcite and quartz). Here we investigate the frictional properties of the clay-rich layers under similar deformation conditions as during the landslide: 1–5 MPa normal stress, 2 × 10−7 to 1.31 m/s slip rate and displacements up to 34 m. Experiments were performed at room humidity and wet conditions with biaxial, torsion and rotary shear apparatus. The clay-rich gouge was velocity-independent to velocity-weakening in both room humidity and wet conditions. In room humidity experiments, the coefficient of friction decreased from 0.47 at v < 5.0 × 10−5 m/s to 0.12 at 1.31 m/s. Microstructural and mineralogical analyses of the gouge after experiments indicate that the dramatic weakening results from thermo-chemical pressurization of pore fluids (smectite decomposition to illite-type clays) and powder lubrication. In wet experiments, the coefficient of friction decreased from 0.17 at v < 1.0 × 10−4 m/s to 0.0 at v > 0.70 m/s: full lubrication results from the formation of a continuous water film in the gouge. The Vaiont landslide occurred under wet to saturated conditions. The unstable behavior of the landslide is explained by the velocity-weakening behavior of the Vaiont clay-rich gouges. The formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero, even without invoking the activation of thermal pressurization. This explains the extraordinary high velocity achieved by the slide during the final collapse.131 23