EXPERIMENTAL CONSTRAINTS ON THE MICROMECHANICS OF BRITTLE FRAGMENTATION DURING EARTHQUAKE RUPTURE

Abstract

Various fault damage fabrics, from gouge in the principal slip zone, to fragmented and pulverized rocks in the fault damage zone, have been attributed to brittle deformation at high strain rates during earthquake rupture. These fault zone fabrics are significant in terms of 1) the information they contain about coseismic deformation mechanisms, 2) the role they play in dissipating energy and contributing to slip weakening during earthquake rupture, and 3) their influence on fault rock mechanical and hydraulic properties. Past experimental work has shown that there exists a critical threshold in stress-strain rate space through which rock failure transitions from failure along a few discrete fracture planes to pulverization. We present new experimental results on Arkansas Novaculite and Westerly Granite in which we quantify fracture surface area produced by pulverization and examine the controls of pre-existing mineral anisotropy on dissipative processes at the microscale. The results have important implications for the partitioning of dissipated energy under extreme loading conditions expected during earthquakes and the scaling of high speed laboratory rock mechanics experiments to natural fault zones.