Multi-scale damage signatures across major strike-slip faults

This thesis presents a compilation of results from studies of active fault zone geometry, structural properties, and macro- and micro-scale damage fabrics. Multi-scale observations using a wide range of techniques were made along the transform plate boundary of the Pacific and the North-American plates. A new method for quantifying fault trace heterogeneity using Geographic Information System was outlined and used on the database of active faults in California. Several parameters were defined for quantifying fault trace heterogeneity and the range or dispersion in the data. The cumulative slip and slip rate proved effective measures of fault zone maturity.;High resolution topographic models acquired by remote-sensing techniques were utilized to demonstrate how damage to the host rock is related to drainage development about a fault, and how the drainage density can be used as a proxy to study damage zone geometry. A strong correlation between drainage density and proximity to the fault was interpreted as an effect of degree of rock damage. Results of damage mapping using drainage density indicate that the northeast side of the SJF is generally more damaged. The observed asymmetry could be geological evidence for a preferred rupture propagation direction, because a preferred propagation direction is predicted to produce asymmetric damage structure that would be recorded in the volume of rock surrounding a fault. The fault damage zone, as inferred from drainage properties, is more pronounced near areas of complexities in the surface trace. Heterogeneities seen in the fault trace can create stress concentrations and are correlated with observations of higher damage levels.;An extensive exploration of the properties of a damage zone phenomenon---pulverized granitic rocks, was performed with an objective of characterizing their chemistry and the changes they undergo due to their proximity to the San Andreas Fault. X-ray Diffraction and X-ray Fluorescence were used to describe the rocks composition, thin sections were used to describe mineralogy and damage fabrics, and a laser particle analyzer was employed to measure the particle size distribution (PSD). SEM images were used to study the PSD of specific damage textures in pulverized rocks. Additionally, a microprobe was used to study the mineralogy of the fragments and the matrix.;The mean particle size in pulverized rocks is mostly fine sand and silt in size and the rock's constituent minerals react similarly to deformation, with no observed size preference in the mineral fractions. The rocks contain evidence of shear deformation, and the observed damage is not homogeneous in its intensity. Fluid-rock interactions and calcite metasomatism occur in spatial context with secondary faults. Observed clay minerals are a result of faulting and damage, not surface weathering. Results point to a mixed-mode deformation of pulverization and shear in the rocks, in conjunction to non-fractal particle size reduction processes, such as mineral alteration. Taking into account pulverized rocks, shear zones, and a wide damage zone, the amount of energy required for creating and maintaining that damage zone is on the order of a few percent of the total released seismic energy.