UC Santa Barbara

Until recently, oceanic crust aquifer properties were estimated from single-borehole experiments and mathematical modeling. This dissertation presents multi-tracer data from a cross-borehole tracer experiment in a hydrothermal system on the eastern flank of the Juan de Fuca Ridge. A rapid tracer breakthrough induced by a ~548 m3 fluid injection suggests that effective porosity is several orders of magnitude lower than bulk material porosity and ridge-parallel anisotropy may have a large effect on fluid flow in shallow ocean crust. Nine years of data suggest that chaotic local convection does not operate on the 102 – 103 m scale encompassing this field site. The low effective porosity precludes application of the conventional point-source model for tracer experiments and necessitates the development of a new conceptual model to explain observed tracer breakthroughs and derive aquifer properties. The average linear flow velocity at this site is found to be ~1 m/d. At the 102 – 103 scale, the representative elemental volume (REV) is constrained for future use in more accurately modeling oceanic crust as a porous medium.