ELASTIC MODELING OF FAULT-DRIVEN MONOCLINAL FOLD PATTERNS

The traces of buried dip-slip faults are often reconstructed by assumi ng that they follow the plan-view patterns of the overlying monoclines and by interpolating between seismic profiles. To place constraints o n such reconstructions, the uplift pattern produced by prescribed slip on a set of buried reverse faults is calculated, assuming that the ov erall plan-view fold pattern is determined by faulting-induced elastic strain, while inelastic relaxation and gravitation only modify the de tails of the finite cross-sectional geometry of the folds. Faults are represented by dislocation planes embedded in an elastic medium which is otherwise continuous and uniform. These assumptions are applied to the monoclines of the Negev (Israel), driven by high-angle reverse fau lts. A first model closely follows the existing structural map, which is based on field mapping and seismic profiles, and is characterized b y long, continuous faults. Slip is taken as uniform and proportional t o fault length. Such a model does not produce either the pattern or th e relative structural elevation of the overlying monoclines, and in pa rticular the observed fold-axis variations. In a second model, we intr oduce fault en-echelon discontinuities and slip gradients at fault ter minations. Relative slip on faults underlying various structures is pr oportional to their observed structural elevations. These features pro duce a reasonable approximation of the overall observed structural con figuration of the monoclines. It can thus be concluded that: (1) the o verall patterns of fault-driven folds are determined by the (coseismic ?) elastic strain field; (2) fault segmentation is a major cause of ob served axis undulations of fault-driven folds; (3) finite dip slip off set at depth is proportional to the observed structural elevation; and (4) along-strike slip gradients account for variations of the structu ral elevation in that direction.