STRUCTURAL AND LITHOLOGIC CONTROLS ON FRACTURE DEVELOPMENT WITHIN A SEGMENTED NORMAL FAULT ZONE, SOUTHERN UTAH
Our analysis revealed changes in fracture network characteristics across the OGB, including: 1) steeply-dipping fracture sets in transition zones display strikes subparallel to the NNE-striking fault segments; 2) fracture sets in some segment footwalls display strikes that deviate ~30 degrees from fault strike; and 3) several locations in segment footwalls display fractures that bend as they approach fault segments. The abrupt changes in fracture set orientations across the OGB may be related to the “open” or “closed” nature of fault segments, which affects the local stress fields by either permitting or preventing stress-field communication across fault segments. We also establish that fracture intensity increases up-section from the lower oxidized zone into the bleached zone, suggesting that changes in cementation may impact elastic moduli and therefore fracture intensity. Our results suggest that as a segmented fault system evolves, fracture network characteristics in transition zones between segments may be more predictable than in footwalls on the margins of the system. Additionally, because fracture networks strongly affect fluid flow in subsurface systems, we can use these results to better predict elevated hydraulic conductivity and flow-rate anisotropy in structurally similar systems.