7. Moab fault, Utah (Imber et al.)

The Moab Fault is a steep normal fault which cuts and exposes a sequence of interbedded sands and argillaceous units ranging from Late Permian to Mid Cretaceous age. Throws of up to 960 m are observed in surface exposures. The footwall and hanging-wall strata are deformed into a series of long-wavelength normal drag folds of variable amplitude that trend NW, approximately parallel to the strike of the Moab Fault. The Moab virtual fieldtrip has been created using terrestrial laser scanning methods to illustrate the sizes and shapes of normal drag zones and the effect of normal drag on fault throw distributions and juxtapositions. From the fieldtrip we can quantify the along-strike variability which places constraints on how to model in flow simulators. In the Moab fault example, drag accounts for c. 30–50% of total throw with a steep inner drag zone (bed dip < 50°) up to 150 m wide, and a more gently dipping outer drag zone (bed dip < 15°) up to 350 m wide. The along-strike 'drag wavelength' of at least 800 m is larger than the grid cell size of a typical flow simulator, implying that normal drag zones should be modelled explicitly to capture their effect on across-fault juxtapositions.