Fault lubrication and earthquake propagation in thermally unstable rocks

Experiments performed on dolomite or Mg-calcite gouges at seismic slip rates (v>1 m/s) and displacements (d>1 m) show that the frictional coefficient µ decays exponentially from peak values (mp≈0.8, in the Byerlee's range), to extremely low steady-state values (µss≈0.1), attained over a w...

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Bibliographic Details
Published in:Geology (Boulder) 2011-01, Vol.39 (1), p.35-38
Main Authors: De Paola, Nicola, Hirose, Takehiro, Mitchell, Tom, Di Toro, Giulio, Viti, Cecilia, Shimamoto, Toshihiko
Format: Article
Language:English
Subjects:
Carbon dioxide
carbonates
Dolomite
Dynamics
Earthquakes
Engineering geology
experimental studies
Faults
friction
gouge
laboratory studies
Microstructure
Nanoparticles
Petrology
physicochemical properties
propagation
rock mechanics
Rocks
Sedimentary geology
Seismic engineering
Seismic phenomena
Seismology
Shear strength
Slip
slip rates
strength
Structural geology
temperature
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Summary:Experiments performed on dolomite or Mg-calcite gouges at seismic slip rates (v>1 m/s) and displacements (d>1 m) show that the frictional coefficient µ decays exponentially from peak values (mp≈0.8, in the Byerlee's range), to extremely low steady-state values (µss≈0.1), attained over a weakening distance Dw. Microstructural observations show that discontinuous patches of nanoparticles of dolomite and its decomposition products (periclase and lime or portlandite) were produced in the slip zone during the transient stage (d>Dw, a slight but abrupt increase in shear strength is observed and interpreted as due to fluids escaping the slip zone. At this stage, dynamic weakening appears to be controlled by velocity dependent properties of nanoparticles developed in the slip zone. Experimentally derived seismic source parameter Wb (i.e., breakdown work, the energy that controls the dynamics of a propagating fracture) (1) matches Wb values obtained from seismological data of the A.D. 1997 M6 Colfiorito (Italy) earthquakes, which nucleated in the same type of rocks tested in this study, and (2) suggests similar earthquake-scaling relationships, as inferred from existing seismological data sets. We conclude that dynamic weakening of experimental faults is controlled by multiple slip weakening mechanisms, which are activated or inhibited by physicochemical reactions in the slip zone.
ISSN:0091-7613
1943-2682
DOI:10.1130/G31398.1