Seismic Modeling of a Strongly Emergent Thrust Front, West Spitsbergen Fold Belt, Svalbard

Abstract

To improve our understanding of the seismic signature of contractional structures in foreland fold-and-thrust belts, seismic modeling of a strongly emergent thrust front was carried out. The modeled structures are a set of well-exposed imbricated fault-bend folds with steep forelimbs and moderately dipping backlimbs, occurring in silicified Upper Permian carbonates and schists. These structures, present at the frontal part of the West Spitsbergen fold-and-thrust belt, are developed above a decollement layer in Permian evaporites. To simulate a synthetic migrated seismic section, image ray modeling was carried out. The acoustic impedances used in the modeling were obtained from laboratory measurements of rock samples. A significant apparent structural (time high), a well as non-real folds and faults, were created by the seismic reflection technique. Without the excellent field control, these structures would have been interpreted as real, indicating deformational features also structurally below the sole thrust in the area. The time high would most certainly survive a traditional depth conversion procedure, and could easily have been misinterpreted as a hydrocarbon trap. High-quality seismic reflection profiles in Isfjorden, paralleling the contraction direction and along strike from the modeled onshore section, show many of the same structural features as in the synthetic model. The seismic modeling demonstrates that care should be exercised when interpreting seismic sections in areas with contractional structures, and suggests that modeling of xposed structural analog is a necessary supplement in detailed seismic studies of such complex contractional geometries.