Fracture Shape and Orientation Contributions to P-Wave Velocity and Anisotropy of Alpine Fault Mylonites

P-wave anisotropy is significant in the mylonitic Alpine Fault shear zone. Mineral- and texture-induced are dominant these rocks but further complicated by presence of fractures. Electron back-scattered diffraction synchrotron X-ray microtomography (micro-CT) data acquired on exhumed schist, protomylonite, mylonite, ultramylonite samples to quantify mineral phases, crystal preferred orientations, microfractures, porosity. The composed quartz, plagioclase, mica accessory garnet, contain 3–5% Based micro-CT data, representative pore shape has an aspect ratio 5:2:1. Two numerical models compared calculate velocity fractured rocks: a 2D wave propagation model, differential effective medium model (3D). results from both have comparable pore-free fast slow velocities 6.5 5.5 km/s, respectively. Introducing 5% fractures with 5:2:1 ratio, oriented longest axes parallel foliation decreases 6.3 5.0 Adding randomly foliation-parallel hinders increase fracture volume. becomes independent porosity when 80% oriented. Modeled 3D different for similar ratios, being 30 15%, This discrepancy result underlying assumptions limitations. Our explain effects that orientations shapes previously published field- laboratory-based studies. Through this study, we show how mica-dominated, compares volume, orientation protolith zone Fault.