CORRELATION BETWEEN VELOCITY DEPENDENCE OF FRICTION AND STRAIN LOCALIZATION IN LARGE-DISPLACEMENT EXPERIMENTS ON FELDSPAR, MUSCOVITE AND BIOTITE GOUGE

Room temperature rotary shear experiments on rock powders of albite fe ldspar and muscovite and biotite micas show that the degree of localiz ation of shear strain in these materials correlates with the frictiona l behavior. In both feldspar and mica experiments, increasing localiza tion correlates with a lower coefficient of friction and a more negati ve velocity dependence of friction. Feldspar gouges tend to have local ized deformation along one or more boundary-parallel shears and a nega tive velocity dependence. More localized deformation correlates with a lower coefficient of friction and a more negative velocity dependence . In general, micas deform throughout a broader zone than feldspar and have a lower coefficient of friction. Compared to muscovite, biotite is weaker, has a negative rather than a positive velocity dependence, and shows more localized deformation. For materials as diverse as feld spars and micas, localization along boundary-parallel shears correlate s with negative velocity dependence. Along compliant natural faults, a negative velocity dependence would result in a greater tendency for u nstable sliding. Thus, localized boundary-parallel shears may indicate negative velocity dependence and slip by earthquakes on natural fault s. (C) 1998 Elsevier Science B.V. All rights reserved.