Abstract. Fault architecture and fracture network evolution (and resulting bulk
hydraulic properties) are highly dependent on the mechanical properties of
the rocks at the time the structures developed. This paper investigates the
role of mechanical layering and pre-existing structures on the evolution of
strike–slip faults and fracture networks. Detailed mapping of exceptionally
well exposed fluvial–deltaic lithologies at Spireslack Surface Coal Mine,
Scotland, reveals two phases of faulting with an initial sinistral and
later dextral sense of shear with ongoing pre-faulting, syn-faulting, and post-faulting
joint sets. We find fault zone internal structure depends on whether the
fault is self-juxtaposing or cuts multiple lithologies, the presence of
shale layers that promote bed-rotation and fault-core lens formation, and
the orientation of joints and coal cleats at the time of faulting. During
ongoing deformation, cementation of fractures is concentrated where the
fracture network is most connected. This leads to the counter-intuitive
result that the highest-fracture-density part of the network often has the
lowest open fracture connectivity. To evaluate the final bulk hydraulic
properties of a deformed rock mass, it is crucial to appreciate the relative
timing of deformation events, concurrent or subsequent cementation, and the
interlinked effects on overall network connectivity.
Fracture Network Connectivity — A Key To Hydraulic Fracturing Effectiveness and Microseismicity Generation
