Fault growth and interactions in a multiphase rift fault network: Horda Platform, Norwegian North Sea Oliver B. Duffy a, * , Rebecca E. Bell a , Christopher A-L. Jackson a , Rob L. Gawthorpe b , Paul S. Whipp c a Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial College, Prince Consort Road, London SW7 2BP, United Kingdom b Department of Earth Science, University of Bergen, P.O. Box 7803, N-5020 Bergen, Norway c Statoil ASA, Sandslivegen 90, 5254 Sandsli, Norway article info Article history: Received 11 March 2015 Received in revised form 28 July 2015 Accepted 30 August 2015 Available online 4 September 2015 Keywords: Normal faulting Multiphase rifting Fault growth Fault interactions Fault throw Fault networks North Sea abstract Physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non-colinear normal fault sets. Furthermore, multiphase rifts will display a greater frequency and range of styles of fault interactions than single-phase rifts. Although these physical models have yielded useful information on the evolution of fault networks in map view, the true 3D geometry of the faults and associated interactions are poorly understood. Here, we use an integrated 3D seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern Horda Platform, northern North Sea. In particular we aim to: i) determine the range of styles of fault interaction that occur between non-colinear faults; ii) examine the typical geometries and throw patterns associated with each of these different styles; and iii) highlight the differences between single-phase and multiphase rift fault networks. Our study focuses on a ca. 350 km 2 region around the >60 km long, NeS-striking Tusse Fault, a normal fault system that was active in the PermianeTriassic and again in the Late Jurassic-to-Early Cretaceous. The Tusse Fault is one of a series of large (>1500 m throw) NeS-striking faults forming part of the northern Horda Platform fault network, which includes numerous smaller (2e10 km long), lower throw (<100 m), predominantly NW eSE-striking faults that were only active during the Late Jurassic to Early Cretaceous. We examine how the 2 nd -stage NWeSE-striking faults grew, interacted and linked with the NeS-striking Tusse Fault, documenting a range of interaction styles including mechanical and kinematic isolation, abutment, retardation and reactivated relays. Our results demonstrate that: i) isolated, and abutting interactions are the most common fault interaction styles in the northern Horda Platform; ii) pre-existing faults can act as sites of nucleation for 2 nd -stage faults or may form mechanical barriers to propagation; iii) the throw distribution on reactivated 1 st -stage faults will be modified in a predictable manner if they are inter- sected or influenced by 2 nd -stage faults; iv) sites of fault linkage and relay-breaching associated with the first phase of extension can act as preferential nucleation sites for 2 nd -stage faults; and v) the devel- opment of fault intersections is a dynamic process, involving the gradual transition from one style to another. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Faults that develop during a single phase of extension typically strike sub-perpendicular to the extension direction and show an en  echelon or colinear configuration (e.g. Gawthorpe and Leeder, 2000)(Fig. 1). Faults with strikes that are oblique to the main rift trend (herein termed ‘non-colinear faults’) can also develop during a single rift phase, commonly due to breaching of relay zones (e.g. Trudgill, 2002), flexure and gravity-driven sliding of the cover above weak layers (e.g. overpressured mudstone or and salt; e.g. Stewart and Clark, 1999) and the development of ‘release’ faults (e.g. Destro, 1995). Furthermore, non-colinear faults also develop in response to: i) perturbations in the local stress field around pre- * Corresponding author. Bureau of Economic Geology, Jackson School of Geo- sciences, The University of Texas at Austin, University Station, Box X, Austin, TX 78713-8924, USA. E-mail address: oliver.duffy@beg.utexas.edu (O.B. Duffy). Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg http://dx.doi.org/10.1016/j.jsg.2015.08.015 0191-8141/© 2015 Elsevier Ltd. All rights reserved. Journal of Structural Geology 80 (2015) 99e119