significance of the low-permeability barrier, if fluid could escape along the decollement

zone. Similarly, lateral fluid escape along the decollement may decrease the impact of

lateral stresses within the prism on k* values within the underthrust sediments. Because

the decollement has been speculated as a possible, yet controversial, pathway for lateral

flow it will be valuable to address in future investigations.

 Implications

 Both simulations using the added lateral stress and low-permeability barrier show a

sharp increase in k* near the decollement zone at both Sites 1174 and 808 (Figure 3-7

and Figure 3-8). However, each scenario generated a distinct k* profile. The k* profile

generated by the added lateral stress demonstrate a gradual increase in pore pressures

both above and below the decollement, and the k* value peak at the decollement. The

maximum k* corresponds to the maximum simulated porosity found near the top of the

decollement zone (Figure 3-7). In contrast, the k* profile generated by the low-

permeability barrier shows an abrupt increase of pore pressures at the lower part of the

decollement. Above the decollement, the k* profile shows a very slight decrease with

depth while below the decollement k* decreases more gradually. As observed in both

scenarios, the maximum k* is located near the decollement, consistent with previous

inferences (e.g., Hubbert and Rubey, 1959) that pore fluid pressures play a major role in

the mechanics of thrust faulting.

 The excess pore pressures observed near the decollement can also be related to the

sliding of the decollement as proposed by the critical wedge theory (Davis et al., 1983).

Critical wedge theory predicts that pore pressures significantly greater than hydrostatic

are needed to maintain small taper angles such as at the Muroto Transect of Nankai.