Experimental and Analytical Models of Extensional Forced Folds: Applications to Gulf of Suez and Offshore Norway: ABSTRACT

Abstract

The authors 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. Folds 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/degree/-35/degree/ 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/degree/, secondary normal faults near the 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,more » well, and field data from extensional forced folds in the Gulf of Suez and offshore Norway.« less