This study uses microstructural characteristics of the San Andreas Fault Observatory at Depth (SAFOD) phase II and III core samples to test specific fault gouge evolution models. These working models are based on a large number of previous field and experimental studies of exhumed fault rocks, simulated fault gouge experiments, and numerical simulations of gouge deformation as well as theoretical considerations of brittle rock deformation and rock friction. The data collection, observations, analyses, and knowledge management are carried out by collaborative teamwork from campuses in the U.S.A. (University of Louisville and Georgia State University), Norway (PGP, University of Oslo), and Italy (University of Padova). The primary questions being investigated are as follows.1. Do gouges undergo a cyclic mechanical behavior while continuous comminution tends to reduce the particle size? If so, how are these processes reflected in the long-term seismic behavior of fault systems? 2. What is the physics of particle size reduction and strain localization in rock gouges? 3. What mechanisms in addition to brittle fracture play a critical role? 4. What proportion of seismic energy is used in gouge particle fracture? The applied methodologies include quantitative microstructural analysis using electron microscopy, analytical techniques, customized image analysis and numerical simulations as well as sub-seismic velocity frictional sliding experiments on the SAFOD gouge samples. The results are available on the Worldwide Web, from several integrated databases and domain ontologies that are being developed and implemented specifically for this project. Results are also being presented and published in scientific conferences and periodicals. These databases and knowledge bases, hosted on a node of the GEON (Geosciences Network) grid (www.geongrid.org) are also accessible from the EarthScope webpage.
