The Growth and Interaction of Faults in Multiphase Rifts: Horda Platform, Norwegian North Sea

Friday, 19 December 2014: 3:10 PM
Oliver B Duffy1, Rebecca E Bell2, Christopher A-L Jackson2, Rob L Gawthorpe3 and Paul S Whipp4, (1)Imperial College London, London, SW7, United Kingdom, (2)Imperial College London, London, United Kingdom, (3)University of Bergen, Department of Earth Science, Bergen, Norway, (4)Statoil Norway Bergen, Bergen, Norway
Analogue models predict that multiphase rifts which have experienced a change in extension direction between stretching phases will typically develop non-colinear normal fault sets and hence will display a greater frequency and range of styles of fault interactions than single-phase rifts. We test these model-based predictions by studying a natural fault network in the northern Horda Platform, northern North Sea using an integrated 3D seismic reflection and borehole dataset. We focus on the >60 km long, N-S-striking Tusse fault that has over 500 m of throw and was active in the Permian-Triassic and again in the Late Jurassic-to-Early Cretaceous. The Tusse Fault forms part of a non-colinear fault network that also comprises numerous smaller (2-10 km long), lower throw (<100 m) and predominantly NW-SE-striking faults that were only active during the Late Jurassic to Early Cretaceous. We examine how the second-stage NW-SE-striking faults have grown and interacted with the N-S-striking Tusse Fault, noting a range of end-member styles of interaction including: i) no interaction; ii) hanging-wall abutting; iii) footwall abutting; iv) cross-cutting; and v) hybrid. To constrain the nucleation and growth history of each of these interaction styles, we systematically apply throw-versus-length (T-x) plots, throw-versus-depth plots (T-z) and 3D throw contouring. This quantitative 3D analysis of the fault network demonstrates: i) pre-existing (first-stage) faults can act as sites of nucleation for second-stage faults; ii) abutting relationships are common and can develop by second-stage faults nucleating either at, or away from pre-existing faults; iii) the throw distribution on reactivated first-stage faults will be modified in a predictable manner if they are intersected or influenced by second-stage faults; and iv) fault segment boundaries, and fault kinks or corrugations along first-stage faults, can act as preferential nucleation sites for second-stage faults, and facilitate the development of complex cross-cutting relationships. In addition to furthering our fundamental understanding of the geometric and kinematic evolution of rift-related normal faults, our results also have broader implications for understanding the physiographic and tectono-stratigraphic evolution of multiphase rift basins.