Abstract - The geometry and hydraulic properties of fault zones are investigated for Mesozoic greywacke basement
and Miocene sandstone from ca 37 km of tunnels in the southern Taupo Rift, New Zealand. Localised
groundwater inflows occur almost exclusively (>90%) within, and immediately adjacent to, fault zones.
Fault zones in the contrasting lithologies comprise fault rock, small-scale faults, and fractures with
thicknesses of 0.01ew110 m approximating power law distributions and bulk permeabilities of 10-9-10-12m2.
Variability in fault zone structure results in a highly heterogeneous distribution
of flow rates and
locations. Within basement ca 80% of the flow rate occurs from fault zones >10 m wide, with ca 30% of the
total localised flow rate originating from a single fault zone (i.e. consistent with the golden fracture
concept). No simple relationships are found between flow rates and either fault strike or hydraulic head,
with <50% of fault zones in any given orientation flowing. A general positive relationship does however
exist between fault zone thickness and maximum flow rate. Higher flow rates from larger fault zones
may arise because these structures have greater dimensions and are more likely (than smaller faults) to
be connected to other faults in the system and the ground surface.
Journal of Structural Geology, 62, 52-64.