Foreword to Special Issue: "Fault Zone Structure, Mechanics and Evolution in Nature and Experiment"
Résumé
Tectonic faults in the Earth's upper crust are geometrically complex zones of localized deformation and rock damage that evolve over wide length- and time-scales. Fault zones influence a range of crustal processes including fluid flow, mechanical strength, basin evolution, and earthquake nucleation, propagation and arrest. Because of this, fault zones motivate considerable academic and commercial research, and have been the focus of a large body of work involving field observations, theory, numerical simulations, experiments and seismology. Despite recent progress, significant aspects of fault zone structure and evolution remain poorly understood. Uncertainties remain as to the main deformation mechanisms that are active during the seismic cycle. It is also largely unclear how deformation is partitioned between principal faults and adjacent regions of off-fault damage, and to what extent associated fluid flow is influenced by varying fracturemodes in different lithologies. A further problem concerns the evolution of fault roughness and fault rock granularity during slip and howthis impacts on fault mechanical behavior. Some of these issues are discussed in this Special Issue of the Journal of Structural Geology which arises from a session held at the EuropeanGeosciences Union (EGU) General Assembly in Vienna, April 2011. The contributions in this volume highlight some of the complexityofnatural fault systems. Common themes that linkmany of the contributions are the relationships between fault zone structure and fault dynamics, and the importance of fault zone structure for sub-surface fluid flow, particularly in fractured carbonates. The 11 papers here are divided in to two parts, although the subdivision is somewhat arbitrary given the multidisciplinary nature of many of the contributions. Papers in Part I, Fault zone structure and evolution, deal mainly with field characterization of fault zones at outcrop to regional scales, and associated observations of fault rock microstructures. Papers in Part II, Fault roughness and brittle rock damage, present field and experimental constraints on the geometry and mechanical properties of fault slip surfaces, pulverized and sheared fault rocks, and cataclastic deformation bands.