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The Influence of Pre-Existing Rift Fabric on Subsequent Fault Array Evolution; An Example From the Horda Platform, Norwegian North Sea

Abstract

An extensive data set consisting high-resolution 2D/3D seismic reflection and well data from the northern Horda Platform (Norwegian North Sea) was used in this investigation of large-scale fault fabric evolution. In any such analysis the validity of interpreted structure is paramount. We present methods for ensuring that framework models are mechanically robust, allowing us to postulate their development with confidence. Many of these methods are inexplicably underused in industry leading to erroneous geometries that devalue the merit of subsequent analysis. Several key, pre-, syn- and post-rift units were identified using seismic-stratigraphic geometry and thickness patterns. A number of key stages of fault growth are observed, the largest N-S trending Permo-Triassic fault systems propagating rapidly through the Jurassic cover to define the locations of the main syn-rift depocentres. Late Jurassic extension was also accommodated by the growth of a second order (NW-SE trending) fault population. These typically occur in the hangingwall regions between the N-S faults, displaying both abutting and cross-cutting relationships with the larger structures. The cessation of this NW-SE trend was coincident with the continued development of the through-going, N-S-striking fault population and the eventual localisation of rift-related strain. The inheritance of a pre-existing rift fabric is observed to influence the scale, rate and geometry of fault system growth and fault array evolution in the cover. The degree of that influence is determined by the scale and maturity of the parent fabric and the temporal initiation of the later fabric within a superseding, rotating stress field. We present a conceptual model that describes the development of large-scale fault fabrics through time, which as an analogue can be readily applied to other parts of the North Sea and beyond.