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| Titel |
Frictional properties of simulated fault gouges of natural dolomite and anhydrite |
| VerfasserIn |
Marco Maria Scuderi, André Niemeijer, Cristiano Collettini, Chris Marone, Dereck Elsworth |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038864
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| Zusammenfassung |
| The integration of seismic reflection profiles with well-located earthquakes shows that the
mainshocks of the 1997-1998 Umbria-Marche seismic sequence (Mmax = 6.0) nucleated at a
depth of ~6 km on normal faults within the Triassic Evaporites (anhydrites and dolomites).
This result appears enigmatic since evaporitic rocks are commonly considered to deform
ductily and thus aseismically. In order to investigate the frictional properties of the Triassic
Evaporites, we performed frictional sliding experiments on simulated fault gouges of natural
dolomites and anhydrites and 50/50 mixtures of the two. Dry and wet experiments were done
in a double-direct shear configuration inside a biaxial loading apparatus using granular
fault gouges at a range of normal stresses (10 - 150 MPa), sliding velocities (1-300
μm/s) and at room temperature and 75 ºC. Under dry and cool conditions all the
lithologies exhibit: i) a brittle behaviour with the coefficient of friction ranging
from 0.6 to 0.7; ii) a velocity strengthening (i.e. stable, aseismic) behaviour. For the
experiments at 75 Ë C, we observe a decrease in the coefficient of friction from 0.65 to
0.44 with increasing normal stress and strain. All the lithologies exhibit a velocity
strengthening behaviour except for the mixtures of anhydrites and dolomites that show an
evolution from velocity strengthening to velocity weakening with increasing sliding
velocity. The microstructures developed during all experiments show a general grain
size reduction from 150 μm to 30-40 μm, with localised deformation and strong
comminution (grain-size 5-10 μm) along B1 and R1 planes. With increasing shear
strain and temperature the R1 planes are more pronounced in particular for the
mixtures of anhydrite and dolomite. Thus at a seismogenic depth of ~6 km, with
increasing temperature and the presence of fluid, the localization of deformation
along planes composed of anhydrites and dolomites, as observed along exhumed
evaporite-bearing faults from the Apennines, may be a mechanical explanation for the
occurrence of frictional instabilities (i.e. earthquakes within the Triassic Evaporites). |
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