Print this pageNumerical Modeling of 
Fault
-Related Folding and Associated
Fluid Flow
STRAYER, LUTHER M., and PETER HUDLESTON
Fault-related folds often show evidence for the involvement of fluids during
deformation in the form of veins, secondary minerals on fracture surfaces, and
stylolites. Fluid flow may occur: a) within the network of discontinuities that
includes bedding planes, faults, and fractures; and b) within the pores in the
continuum. We investigate such behavior using the numerical code FLAC, creating
models of fault-related folds, with and without coupled fluid flow. The rock
layers are given elastic-plastic Mohr-Coulomb constitutive relations. Dilation
angle, cohesion, porosity, and permeability are also defined. Interfaces and
faults are assigned normal and shear stiffnesses, coefficient of friction and
cohesion. In these simulations only flow through the continuum is considered.
Our results in 'dry' rock show that fold style depends on the relative
rigidity of hangingwall and footwall, friction along the fault, fault 'dip',
fault displacement, and the relative ease of local to far-field slip on the
fault. Fold styles include fault-bend and fault-propagation types. Our initial
'wet' simulations indicate there is significant fluid flow that is driven only
by pressure changes associated with fault movement. In the region around the
hangingwall and footwall layer-boundary cutoffs, voids open up during stages of
the simulation, consistent with the presence of secondary minerals in similar
locations in nature. Other simulations show strong coupling between dilational
strain, pore-fluid pressure, and fluid flow. The latter is focused within zones
of localized plastic flow that simulate brittle deformation and fault
development in nature.