Edited version
"Heating and Weakening of Shear Zones in Landslide and Earthquake Mechanics"
James R. Rice, Harvard University
ABSTRACT: Field and borehole observations of active earthquake fault zones show that shear is often highly localized to principal deforming zones of order 10s of microns to a few mm wide. Landslides in relatively homogeneous soils, especially clays, or in layered strata can likewise exhibit extremely narrow shear zones. Those two domains of study, landslide and earthquake mechanics, reached relative maturity with, it seems, nearly total ignorance of researchers in one field about developments in the other. Ioannis Vardoulakis was a great exception, avidly advancing the science of both fields and, shortly before his tragic passing in his 60th year, co-organizing (with Y. Hatzor and J. Sulem) the unifying Batsheva de Rothschild conference on "Shear Physics at the Meso-scale in Earthquake and Landslide Mechanics", held January 2009 in Ein-Gedi, Israel. The lecture will follow Ionanis to explain narrow shear zone development as a thermo-hydro-mechanical process in wet granular media. In it, highly elevated pore pressure is a predicted and lab-verified consequence of rapid straining, which enables intense shear localization. That pressurization can develop in fluid which pre-exists in the gouge as groundwater, or in volatile phases emerging at high pressure from thermal decomposition reactions in hydrated silicates (clays, serpentines) or carbonates. The concepts when applied, e.g., to fault zones, show how fault materials with high static friction coefficients, ~0.6 to 0.8, can nevertheless undergo highly localized shear at effective dynamic friction coefficients of order 0.1, thus fitting observational constraints of producing negligible surface heat out-flow and rarely creating extensive melt.
