Structural geology & fault zones
Understanding the geologic structure, slip history, and stress-related permeability evolution of fault zones is of great interest for evaluating seismic hazards, studying regional tectonic histories, and producing oil, gas, and geothermal resources. I recently conducted a detailed study of a rare exposure of a fault zone in the footwall of the Alpine Fault system in the South Island of New Zealand with Virginia Toy and Klaus Gessner, to understand its permeability evolution and slip history. We found that the slip vector and associated mineralized microfaults have kinematics compatible with slip in the current stress field. Despite this, the principal slip surface is poorly oriented for slip in the present stress state, and it appears that small, well-oriented, mesoscale faults have subsequently developed that cross the main fault zone. This fault zone thus represents rare evidence of plastic strain consistent with the present stress field occurring in the Pacific Plate footwall of the Alpine Fault in this area.
Looking east from near Okarito, New Zealand, across the Alpine Fault, to the Southern Alps. Mount Cook is the highest peak, near the right side.
Annotated images extracted from a 3D whole-outcrop photo stitch depicting the principal slip zone, fault core, and damage zone of the Smithy Creek fault, South Island, New Zealand (from Lund Snee et al., 2014).