The physical and mechanical properties of natural fault zones in basaltic volcanic rocks

Fractured basaltic rocks are critical to the strength of volcanic systems, including volcanic islands and Large Igneous Provinces. Fractured and faulted regions control rock mass strength, owing to the variability in hydraulic properties (limiting or focusing fluid flow in the crust), and to the change in mineralogy; strong crystalline rocks are replaced by relatively weak and interconnected clays, related to fluid-mediated alteration. It is important, therefore, to determine the strength of the components of natural faults and fractures, and the distribution of those components, for a range of geologic processes, such as:

1. Slope and edifice collapse;
2. fault and fracture propagation and surface rupture;
3. seismogenic slip nucleation versus creeping deformations; and
4. fault and fracture reactivation during natural or induced fluid pressure cycling.

The latter of these processes is becoming increasingly important in the challenges of green energy, such as in high-temperature geothermal energy systems and for carbon storage sites.

Previous studies have sought to constrain basalt-hosted fault rock geomechanical properties using experimentally-induced fractures. This project will focus on natural fault and fracture systems, using exceptionally preserved fault rock assemblages in the Faroe Islands, NE Atlantic margin. Faults in the Faroe Islands accommodate mm- to (potentially) km-scale displacements, and record single to multi-stage events (Walker et al., 2013a,b), and display a range of mineral products related to fluid-rock interactions (Walker et al., 2012; 2013a,b). The project will characterise fault rock assemblages across a range of observation scales, including detailed field-based fault geometric data using photogrammetry and traditional techniques, and microscale characterisation using 3D micro-CT imaging. Structural work will be paired with geochemical analysis, to determine the fluid-mediated exchange processes. Collected fault rock samples will be prepared for experimental rock deformation experiments, to determine rock physical, mechanical, and fluid flow properties, and provide the first systematic tests of rock strength for natural faults at a range of simulated conditions.