Shear tests on intact fault gouges preserving natural deformation fabrics

Abstract

Deformation fabrics developed in natural fault gouges are one of the critical factors leading to fault weakness. However, the possible effects of the deformation fabrics on various frictional properties of fault rocks have been almost unexplored. In this study, we developed new equipment for taking intact gouges in a wafer form, conducted preliminary shear tests on the wafer specimen, and compared the experimental results from the wafer specimen with those from other gouge specimens (water-saturated and paste specimens) that were prepared in the conventional methods. For the friction coefficient, the wafer specimen showed the lowest value (similar to 0.25), while the paste and saturated specimens showed similar to 0.3 and 0.3-0.4, respectively. For the frictional stability and frictional healing, all the gouge specimens showed velocity-strengthening (a-b > 0) behavior, which is related with an intrinsically stable fault slip, and very low (nearly zero) healing rate. It is noteworthy that the wafer specimen showed the lowest a-b value and negative healing rate. The preliminary results indicate that the deformation fabrics may affect not only frictional strength but also other critical mechanical properties (e.g., frictional stability) of faults.