An empirically based steady state friction law and implications for fault stability.
Empirically based rate-and-state friction laws (RSFLs) have been proposed to model the dependence of friction forces with slip and time. The relevance of the RSFL for earthquake mechanics is that few constitutive parameters define critical conditions for fault stability (i.e., critical stiffness and frictional fault behavior). However, the RSFLs were determined from experiments conducted at subseismic slip rates (V< 1 cm/s), and their extrapolation to earthquake deformation conditions (V> 0.1 m/s) remains questionable on the basis of the experimental evidence of (1) large dynamic weakening and (2) activation of particular fault lubrication processes at seismic slip rates. Here we propose a modified RSFL (MFL) based on the review of a large published and unpublished data set of rock friction experiments performed with different testing machines. The MFL, valid at steady state conditions from subseismic to seismic slip rates (0.1 µm/s <V< 3 m/s), describes the initiation of a substantial velocity weakening in the 1-20 cm/s range resulting in a critical stiffness increase that creates a peak of potential instability in that velocity regime. The MFL leads to a new definition of fault frictional stability with implications for slip event styles and relevance for models of seismic rupture nucleation, propagation, and arrest.
Istituto Nazionale di Geofisica e Vulcanologia Rome Italy.
E
E
Spagnuolo
Department of Earth Sciences University of Durham Durham UK.
S
S
Nielsen
LEMR, ENAC, École polytechnique fédérale de Lausanne (EPFL) Lausanne Switzerland.
M
M
Violay
Istituto Nazionale di Geofisica e Vulcanologia RomeItaly; School of Earth, Atmospheric and Environmental Sciences University of Manchester Manchester UK; Dipartimento di Geoscienze Università degli Studi di Padova Padua Italy.
G
G
Di Toro
earthquake mechanics; fault stability; fault stiffness; friction laws; slip events
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