Mechanics, Structure and Evolution of Fault Zones

The brittle portion of the Earth’s lithosphere contains a distribution of joints, faults and cataclastic zones that exist on a wide range of scale-lengths and usually have complex geometries including bends, jogs, and intersections. The material around these complexities is subjected to large stress concentrations, which lead during continuing deformation to the generation of new fracture and granular damage with an associated evolution of the elasticity, permeability and geometry of the actively deforming regions. The evolving material and geometrical properties within and around the fault zone can lead, in turn, to evolution of various aspects of earthquake and fault mechanics. The geometrical complexity, material heterogeneities and wide range of effective space-time scales make the quantification of properties and processes associated with fault zones extremely challenging. Many fundamental questions concerning the mechanics, structure and evolution of fault zones remain unanswered despite considerable research spanning over 100 years. The fourteen papers in this volume provide recent theoretical and observational perspectives on fault zones. Topics include damage and breakage rheologies, development of instabilities, fracture and friction, dynamic rupture experiments, analysis of geodetic data, and geological and laboratory characterizations of fault traces, fault surfaces, fracture zones, and particles in rock samples from fault zone environments. FINZI et al. present computer simulations of the evolution of geometrical and elastic properties of large strike-slip fault zones and associated deformation fields, using a model with a seismogenic upper crust governed by a continuum damage rheology. The fault zones form initially as complex segmented structures and evolve overall with continuing deformation toward contiguous simpler structures. The simulations generally produce flower-type structures, consisting of a broad damage zone in the top few kilometers and highly localized damage deeper. However, at persisting geometrical complexities significant damage extends throughout the seismogenic zone. DE JOUSSINEAU and AYDIN discuss observed geometrical properties of surface traces of strike slip faults in the Valley