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| Titel |
Sliding behavior of calcite and dolomite marbles at seismic deformation conditions |
| VerfasserIn |
Elena Spagnuolo, Steven Smith, André Niemeijer, Stefan Nielsen, Giulio Di Toro |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056986
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| Zusammenfassung |
| Our understanding of earthquake physics is hampered by the poor knowledge of the evolution
of the friction coefficient in rocks (μ or the ratio of shear stress over normal stress) at
deformation conditions typical of the seismic source (normal stress > 40 MPa, slip rates V >
1 m/s, abrupt accelerations, etc.). Insights can be gained by experiments using a novel rotary
shear deformation apparatus, SHIVA (Slow to HIgh Velocity Apparatus) which, by exploiting
the large available power (300 kW), is capable of extending the performance of
previous experimental apparatus to more realistic (i.e. natural) conditions. Here we
present results from experiments performed on samples of Carrara (98% calcite) and
dolomitic (98% dolomite) marbles. The two rocks were selected because (1) many
earthquakes worldwide nucleate within and rupture through carbonates sequences (e.g.,
L’Aquila 2009 Mw 6.3) and (2), both rocks release CO2 during thermal decomposition;
dolomite at about 550°C and 800°C, and calcite at 800°C; thus the different frictional
evolution of the two rocks can be correlated to different decarbonation stages and
temperatures.
Tests were conducted on hollow cylinders (50/30 mm ext/int diameter) at V of 0.1–6.5 m/s
and normal stresses up to 40 MPa. Each experiment consists of three steps: (1) loading of the
sample to the target normal stress; (2) acceleration to the imposed slip rate; (3) deceleration
until the target slip or duration is reached.
At V < 0.3 m/s calcitic and dolomitic marble have a μ of about 0.5. At V -¥ 1 m/s, in both
rocks, μ increases to a peak value (~ 0.6) in the first few mm of slip, followed by an
exponential decay towards an extremely low steady-state value (« 0.1), as previously
observed in experiments performed at lower normal stresses (< 13 MPa, Han et al., 2007;
2010). However, in dolomitic marble, the decay distance is shorter and complicated by a
short-duration phase of re-strengthening (after about 0.5 m of slip): this complex weakening
behaviour might result from the occurrence of two decarbonation reactions (at 550°C and
800°C, respectively).
At V < 0 .3 m/s, calcitic and dolomitic marble shorten significantly (0.2-0.3 mm of shortening
per m of slip at 10 MPa normal stress) due to bulk fracturing and loss of gouge
material from the sliding surface. Instead, shortening rate decreases with increasing
slip rate. At V -¥ 1 m/s, shortening of calcitic marble is negligible ( |
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