The propagation and linkage of normal faults: Insights from the Strathspey-Brent-Statfjord fault array, northern North Sea

Abstract

Through examination of the scaling relations of faults and the use of seismic stratigraphic techniques, we demonstrate how the temporal and spatial evolution of the fault population in a half-graben basin can be accurately reconstructed. The basin bounded by the >>62 km long Strathspey-Brent-Statfjord fault array is located on the western flank of the Late Jurassic age northern North Sea rift basin. Along-strike displacement variations, transverse fault-displacement folds and palaeo- fault tips abandoned in the hangingwall all provide evidence that the fault system comprises a hierarchy of linked palaeo-segments. The displacement variations developed while the fault was in a pre-linkage, multi-segment stage of its growth have not been equilibrated following fault linkage. Using the stratal architecture of syn-rift sediments, we date the main phase of segment linkage as latest Callovian - Middle Oxfordian (10-14 M.yr. after rift initiation). A dense sub-population of faults is mapped in the hangingwall to the Strathspey-Brent-Statfjord fault array. The majority of these faults are short, of low displacement and became inactive within 3-4 M.yr. of the beginning of the extensional event. Subsequently, only the segments of the proto- Strathspey-Brent-Statfjord fault and a conjugate array of antithetic faults located 3.5 km basinward continued to grow to de fine a graben-like basin geometry. Faults of the antithetic array became inactive approximately 11.5 M.yr. into the rift event, concentrating strain on the linked Strathspey-Brent-Statfjord fault; hence, the basin evolved into a half-graben. As the rift event progressed, strain was localised on a smaller number of active structures with increased rates of displacement. The results of this study suggest that a simple model for the linkage of 2-3 fault segments may not be applicable to a complex multi-segment array.