LABORATORY-DERIVED FRICTION LAWS AND THEIR APPLICATION TO SEISMIC FAULTING

This paper reviews rock friction and the frictional properties of eart hquake faults. The basis for rate- and state-dependent friction laws i s reviewed. The friction state variable is discussed, including its in terpretation as a measure of average asperity contact time and porosit y within granular fault gouge. Data are summarized showing that fricti on evolves even during truly stationary contact, and the connection be tween modern friction laws and the concept of ''static'' friction is d iscussed. Measurements of frictional healing, as evidenced by increasi ng static friction during quasistationary contact, are reviewed, as ar e their implications for fault healing. Shear localization in fault go uge is discussed, and the relationship between microstructures and fri ction is reviewed. These data indicate differences in the behavior of bare rock surfaces as compared to shear within granular fault gouge th at can be attributed to dilation within fault gouge. Physical models f or the characteristic friction distance are discussed and related to t he problem of scaling this parameter to seismic faults. Earthquake aft erslip, its relation to laboratory friction data, and the inverse corr elation between afterslip and shallow coseismic slip are discussed in the context of a model for afterslip. Recent observations of the absen ce of afterslip are predicted by the model.