Studies of the aspect ratios of nearly 400 mineral-filled veins in the on-land parts of the Húsavík-Flatey fault on the Flateyjarskagi peninsula have been carried out by Á. Guðmundsson. They indicate that the average fluid overpressure with reference to the minimum compressive principal stress, at the time of vein emplacement, was around 20 MPa. In the current model on fluid transport along fault zones, it is proposed that during transport of overpressured fluids, such as are commonly associated with seismogenic faulting, the hydraulic conductivity of the damage zone can greatly increase. An overpressured fluid increases the apertures of the fractures constituting the network of the damage zone, and as a consequence the volumetric flow rate can, temporarily, be several hundred times greater than during fluid flow under hydrostatic pressure. Similarly, during periods of seismogenic faulting along the core, its hydraulic conductivity, and the associated transmissivity (conductivity times core thickness), may increase by many orders of a magnitude. As an example, a single fault plane along the core with an aperture of only 0.1-1 mm can transmit many hundred to many hundred thousand times more water than a porous fault core, tens of meter thick and with high values of hydraulic conductivity. This model may partly account for the great volumes of water that are commonly inferred or observed to be transported during seismic activity in large-scale fault zones.