3D seismic reflection analysis of fault growth, rift basin geometry and the role of pre-existing structural fabrics Dr Christopher Jackson Dr Rebecca Bell The growth and linkage of fault segments to form continuous, basin-bounding normal fault zones is recognised as a first-order control on the size and shape of rift basins, their geomorphology and their sedimentology and stratigraphy (e.g. Prosser 1993; Anders and Schlische 1994; Gawthorpe et al. 1994; Gawthorpe and Leeder 2000; Cowie et al. 2000, 2006). Large normal fault systems develop when strain localises in the lithosphere, and pre-existing basement structure plays an important role in determining where and how fast strain becomes localised because of its influence on lithospheric strength. Fault segmentation and branching, as well as the distribution of displacement in 3D, are also strongly determined by underlying basement and cover structure (e.g. Henza et al. 2010, 2011; Frankowicz and McClay 2010; Allken et al., 2011). These factors have a major impact on the size, geometry and compartmentalisation of normal faultrelated structural traps and on the localisation of fluid migration pathways at both geological and production timescales. Basement structure also plays an important role in determining the paleotopography/bathymetry and the paleogeography as well as the source areas and sediment routing at the onset of extension. The pre-rift landscape becomes modified as normal fault growth changes the distribution of uplift/subsidence and hence the geomorphic rates and processes also change. The way in which the landscape responds to this ‘tectonic perturbation’ has important implications for understanding synrift stratigraphy and particularly the location, geometry and heterogeneity of syn-rift reservoirs. Furthermore, recent work (e.g. Maniatis et al. 2009) suggests that syn-rift erosion and deposition, through transferring mass from one location to another, will feedback to also control the structural style and activity on normal faults and rift basin geometry. Although many rift basins have undergone multiple phases of rifting, a detailed understanding of the influence of pre-existing structure on fault growth and synrift stratigraphy is lacking. For example, the Jurassic North Sea rift system was built on the Permo-Triassic rift, which in turn was influenced by earlier basement heterogeneities, many of which were related to the Caledonian orogeny and post-Caledonian Devonian transtension. Any in-depth attempt to relate fault orientations and fault growth during the later rift events must therefore consider the impact of structures existing prior to the particular extension phase. The main aim of this project is therefore to develop a fundamental understanding of how pre-existing structures in both basement and cover influence the evolution of normal faults and normal fault populations on rifted margins. We will use this understanding to analyse the geomorphological evolution of rifts and the impact this has on erosion, sediment transport pathways and the overall evolution of syn-rift depositional systems. Our main aim will be achieved through a series of specific objectives: To investigate how pre-existing basement and cover structures influence the nucleation, growth, interaction and linkage of normal fault segments and their organisation and evolution within multi-phase rift basins. To establish how pre-existing structures influence the evolution of rift basins and use this analysis to understand the controls on rift topography, sediment sources, major sediment transport pathways and depositional systems in multi-phase rifts. To quantify the effects of erosion, deposition and mass redistribution at the Earth’s surface on fault evolution and rift basin morphology where pre-existing structures exert a strong control on fault development. To achieve these objectives we will use a large (1000 km2), high-resolution (25 m line spacing), 3D seismic reflection dataset from offshore NW Australia. In these data a number of fault populations, which display different geometric relationships are clearly imaged. Detailed three-dimensional mapping of key faults and seismic horizons will form the foundation for a detailed, quantitative analysis of the present-day geometry of the fault network, and investigation of the temporal evolution of the fault population. The results of this study will be used by the petroleum industry to: a) understand more clearly the controls on, and variability of, structural traps related to normal faulting, and b) develop models for subtle syn-rift plays. Thus the project will contribute to reducing exploration risk and increasing the sophistication of synrift reservoir models. Although we will use seismic reflection data from offshore Australia, the generic understanding of normal fault growth and the associated evolution of syn-rift sedimentary systems will be applicable to rifted margins world-wide.