Negative structural inversion: an overview

Abstract

The same sense movement on any given fault plane occurs much more frequently compared to the cases when the sense reverses. Therefore, positive or negative structural inversions are regarded as special cases within the much more general and typical process of fault reactivation.Extensional reactivation of former reverse faults or, specifically thrust planes in thrust fold belts, designated as “negative inversion”, received much less attention by both the petroleum industry and the academia than the opposite process.Based on the structural review of many case studies of positive and negative inversion they display contrasting kinematic patterns. One of the obvious structural differences is related to the geometry of short-cut structures developed during the more advanced stage of inversion. In the case of positive inversion, a short-cut thrust develops within the footwall of the major inverted fault to better accommodate the ongoing shortening. In contrast, a short-cut normal fault develops within the hanging wall of the partially inverted master fault during negative inversion.Based on a worldwide compilation there are examples of hydrocarbon fields with valid traps associated with negative inversion. Therefore, we suggest that even though negative inversion may not be as important for petroleum exploration as its positive counterpart, yet, it may produce more traps in the internal parts of thrust fold belt than currently perceived.At present, case studies of negative inversion defined by the extensional reactivation of pre-existing thrust planes are relatively rare, compared to the more frequent documentation of positive structural inversion in published literature. Whether this disparity between negative and positive inversion is a result of non-observation in the subsurface, at the expense of the former, or it is caused by a more fundamental structural difference between the two processes, it remains to be seen.