Plastic faulting: Brittle‐like failure under high confinement

Abstract

[1] Two distinct modes of compressive brittle-like failure are observed in laboratory samples of rock and ice. Under low to moderate confinement, terminal failure follows microcrack growth and interaction when damage is localized along a fault oriented $30°t o the greatest compressive stress. Under higher confinement, frictional sliding is suppressed, and sudden, localized, brittle-like failure is not attended by a concentration of microcracks near the main fault. Also, faults that form under higher confinement are narrower and oriented $45°to the greatest compressive stress. We propose that these more steeply inclined faults are plastic faults whereby deformation is localized because of an instability that develops when thermal softening exceeds strain hardening. Analysis leads to a quantitative model for the shear stresses required to initiate and maintain the instability and to accommodate slip along the fault. The required stress is in general agreement with observed failure stresses from a variety of crystalline materials. Application of this model suggests that in some cases plasticity, rather than friction, limits the strength of the Earth's upper crust.

The Subductability of Continental Lithosphere: The Before and After Story

“…3.9a). When yield stresses in better agreement with experimental results are used (e.g., Shimada 1993;Renshaw and Schulson 2004), the volume of detached oceanic crust decrease, but do not cease to occur in our models ( Fig. 3.9d).…”

Superplasticity and ductile fracture of synthetic feldspar deformed to large strain

“…It is conceivable that cavitation may contribute to an enhanced permeability and fluid flow localized in shear zones that is frequently observed [Rutter and Brodie, 1985]. Unstable ductile failure in mylonite shear zones at the base of the seismogenic upper crust has been suggested as a possible source mechanism for earthquakes [Hobbs and Ord, 1988] and pseudotachylytes at great depth [Austrheim and Boundy, 1994;Hobbs et al, 1986;White, 1996;Renshaw and Schulson, 2004]. Failure is often attributed to shear heating and/or dehydration reactions and possibly transient fluid pressure pulses.…”

The fracture of water ice Ih: A short overview

“…Iliescu and Schulson (2004) describe this new process and present a physical model that is based upon the competition between wing crack growth and Euler buckling of deformation-produced thin plates. Under triaxial confinement greater than that required to suppress frictional sliding, plastic faults develop (Schulson 2002b), a failuremode transition that is again seen in rocks and minerals (Renshaw and Schulson 2004).…”