he relevance of intersections in enhancing fluid flow through fractured-controlled systems has been recognized across a wide range of scales, however, the magnitude of the enhancement of fractured rock permeability provided by intersections has not yet been quantified. This project examines the hydraulic and mechanical properties of intersections through a multi-scale approach, from measuring the permeability of the intersection between two fractures in the laboratory, to determining the mechanical interaction between three, kilometer-length, plate boundary segments intersecting at a tectonic triple junction. For the first part, synthetic intersections between two tensile fractures were generated in samples of Seljadalur Basalt, whose permeability was measured as a function of pressure and compared with single fracture permeability. Results indicate that fracture intersections are significantly more permeable and less compliant than two macro-fractures, which led to the formulation of a physical model of the pressure dependence of intersection permeability based on the elastic compressibility of the intersection cavity.
Next, the local deformation processes occurring at the site of intersecting plate boundaries were studied at the active, subaereal, Hengill Triple Junction, host of the most productive geothermal region in Iceland. Detailed structural mapping at the outcrop scale was performed to develop a conceptual model of pathways and compartmentalization for meteoric and hydrothermal fluids, to be used as analogue to the subsurface, reservoir rocks. Finally, regional-scale mapping allowed to examine the local interplay of three converging tectonic regimes and their effect on the structural configuration and stress fields within the triple junction region. These results may have direct implications for the on-going geothermal operations in terms of the spatial variability of structural permeability and induced seismicity hazards.