Effects of fault-gouge on the frictional properties of rocks : an experimental study
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Date
1977
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Abstract
The effects of fault gouge on the sliding behavior of rocks are studied experimentally to gain a better understanding of the mechanism of shallow focus earthquakes along pre-existing natural faults. Nearly 200 specimens of Tennessee sandstone with various gouges along a 35° precut are deformed dry in a triaxial apparatus, at room temperature, -4 shortening rates of about 5 x 10 /sec, and confining pressures to 3 kb. A mechanical model is developed to describe stick-slip in the experimental system. It is shown that under plausible assumptions, stickslip in the triaxial system becomes mathematically analogous to that in a simple, spring/mass/slider-block system. The theory agrees well with the experiments with respect to the cosine form of the displacement time function, a constant rise time of stick-slip, and a linear relation between the force drop and the average particle velocity. Based on the stick-slip model, it is argued that differences in the behavior among various gouges are due primarily to the differences in the frictional properties of specimen along the sliding surface; i.e., inertial and elastic properties of the experimental system are lit t le influenced by gouge type. Sliding behavior depends markedly on the material used as the gouge. Experimental results from monomineralic gouges show that Mphs' hardness of a mineral is a useful parameter to predict the general behavior of gouge. The most unstable behavior is associated with gouge composed of minerals with intermediate hardness (dolomite, anhydrite and calcite); these gouges undergo the transition from stable sliding to stick-slip at about 0.5 - 0.8 kb. Gouge composed of hard minerals such as quartz or feldspar behave more stably, but stick-slip occurs at pressures above 2.5 kb. Only stable sliding is observed for gouge composed of soft minerals like halite.
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Keywords
Earthquake prediction, Faults (Geology), Rock mechanics, Major geology