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.