vertical flow, this relationship may be more appropriate for the simulations than the best

fit equation. However, if the high excess pore pressures suggested by Screaton et al.

(2002) or Saffer (2003) are correct, permeabilities must be even lower, requiring either a

bulk permeability represented by log (ko) = -20.82, a low permeability (<10-20 m2) barrier

above the decollement, or a combination of lower bulk permeability and permeability

barrier. Alternatively, other factors must contribute, such as recent prism growth rates

greater than the time-averaged rates simulated here.

 The magnitude of pore pressures in the underthrust sediments demonstrated only

slight sensitivity to added lateral stresses in the prism, although the profile of the pore

pressure ratio is affected. Results further illustrated that the simulations with low-

permeability barrier and lateral stress both produced a sharp increase in porosities below

the decollement zone, as is observed in the measured values. Furthermore, in both

scenarios, maximum excess pore pressure ratios were found at the decollement, which

could contribute to stable sliding of the decollement zone.