and increasing to more than 80% of lithostatic pressures at total depth (Moore and
Vrolijk, 1992).
Basics of Fluid Flow Related to Subduction Zone
Although sediments found in accretionary prisms are highly deformed during
subduction, it is assumed that the high density and interconnectedness of the fractures in
accretionary prisms approximate Darcian flow (Moore and Vrolijk, 1992). The fluid
produced during the accretionary process can be evaluated using the two principles that
govern fluid flow in the subsurface. They are the principle of conservation of mass and
Darcy's law. The principle of conservation of mass states that for an arbitrary control
volume, the rate of mass accumulation within the volume plus the net mass flux out of
the volume must equal the rate of mass generation within the volume (Bird et. al., 1960).
If we consider a very small volume of the aquifer known as a control volume, we can
approximate the flow through the matrix using Darcy's law. The most basic form of
Darcy's law states
Q/A=-K dh/dl
where Q/A is flow per area or linear velocity [LT-1], K is hydraulic conductivity [LT1],
and dh/dl is hydraulic gradient. The hydraulic conductivity (K), which is a
proportionality constant, represents both properties of the fluid and the porous media. It
is given by
K= kpg/[t
where k is intrinsic permeability [L2], which is representative of the properties of the
porous medium, p is the fluid density [ML-3], [[ is the fluid viscosity [L-1 T-1] and g is the
gravitational constant [L T-2]. Intrinsic permeability depends on variables such as grain