Analysis of
Fault Network and Rock Mass Connectivity in Pull-apart Basins
Sims, Darrell W.1, Alan P.
Morris1, Kevin J. Smart1, David
A. Ferrill1
(1) Southwest Research Institute®, San Antonio, TX
Fault system geometry of pull-apart
basins is often complex and difficult to interpret from two- or even
three-dimensional seismic data. This is particularly the case for the
interpretation of steeply-dipping to vertical faults. Here we examine lateral
and vertical fault network and rock mass connectivity of a pull-apart basin
developed over a ductile detachment. We used analogue methods so that
pull-apart development in plan view could be closely observed and documented.
Our scaled models consisted of a horizontal color-layered sandpack over a thin
(0.5 cm) layer of silicone putty. Final subsurface fault geometry was obtained
by vertical, closely spaced (< 1cm) serial cross-sections coupled with map
view images of the developing model upper surface. We use the following method
to perform the analyses. The cross-sections and map view are photographed and
converted to digital images. The cross-section and final plan-view images are
co-registered to a common reference frame and imported into three-dimensional
seismic interpretation software. Fault traces and contacts between colored sand
layers are converted to two-dimensional fault and horizon surfaces to create a
three-dimensional visualization of layers and faults throughout the pull-apart
system. Fault trace maps are taken from sequential vertical and horizontal slices
through the three-dimensional visualization model. Fault network connectivity
and rock mass connectivity are then calculated for each slice. Our results
indicate that basin fault systems become increasingly complex with increased
depth, producing an overall increase in horizontal fault network connectivity
with depth and, conversely, a decrease in rock mass connectivity. Lateral
variability in connectivity at depth is observed along basin strike, and is not
predictable from surface fault trace maps.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California