Experimental and Analytical Models of Extensional Forced Folds: Applications to Gulf of Suez and Offshore Norway
Jon E. Olson, Martha O. Withjack
We have studied the structural development of extensional forced folds (i.e.,
folds that form above normal faults) using single-layer and multilayer clay
models and analytical models of dislocations in an elastic half-space. The
single-layer clay models and dislocation models show that extensional forced
folds are narrow, monoclinal flexures with steep limb dips near the tip of the
underlying master normal fault. Fold widths increase and limb dips decrease
upward. Secondary faults initiate at the tip of the master normal fault, are
subparallel to it, and curve 25°-35° into its hanging wall as they propagate
upward. Consequently, secondary fault patterns depend on the dip of the master
normal fault. If the dip is less than 60°, secondary normal faults near t e tip
of the master normal fault become high-angle reverse faults at shallow depths.
The propagation and eventual linkage of these secondary faults terminates the
development of extensional forced folds. Less folding occurs prior to fault
linkage if the master normal fault is gently rather than steeply dipping. In
multilayer clay models that allow interlayer slip, extensional forced folds are
wider and limb dips are gentler than those in the single-layer models. These
modeling
results provide guidelines for interpreting
seismic
, well, and field
data from extensional forced folds in the Gulf of Suez and offshore Norway.
AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.