hemipelagic and turbidite units whereas in Bekins et al. (1995), all sediment units were

treated as hemipelagics. In the base run, for hemipelagics, the same permeability-

porosity relationship (log (k) = -22.0+8.45n) as in Bekins et al. (1995) was used. For

turbidites a relationship with higher permeability was used (log (k) = -20.0+5.25n). In

addition, the decollement was assigned the same permeability-porosity relationship as for

the hemipelagic sediments instead of using a higher permeability value as in Bekins et al.

(1995) simulation. The results of the base run indicate that maximum k* extends from

about 4 km arcward from the deformation front and laterally extends arcward with time

(Figure 4-3). At all four time periods, the maximum k* value is contained in the area

directly below the prism. During the first 0.6 million years, the maximum X* reached a

value of 0.89 in the underthrust sediments and 0.9 in the decollement. Both values

increased by 0.03 between 0.6 and 1.3 million years. After reaching a maximum X*

values of 0.93 in the underthrust and 0.94 in the decollement at the end of 2 million years

the maximum X* values decreased to 0.90 at 2.7 million years. This decrease in k* value

with time may have result from the dissipation of pore pressures during the 2.7 million

years of subduction. It may be possible that some fluid will flow arcward within the

turbidite layer (although it cannot flow out of the arcward boundary) thus, decreasing the

peak pore pressures in the decollement and underthrust with time. Calculations by

Hanshaw and Bredehoeft (1968) shows that even if a high pore pressure region is

surrounded by a low-permeability (10-21 m2) material the pore pressures cannot be

maintained above 75 percent of the lithostatic stress for more than 10,000 years. Based

on these calculations, the excess pressures bleed off with time because the specific

storage, which is a function of the pore volume and the compressibility of water and rock