Quantifying the growth history of seismically imaged normal faults Edoseghe E. Osagiede a, b , Oliver B. Duffy b, * , Christopher A.-L. Jackson b , Thilo Wrona b a Department of Earth Sciences, University College London, WC1E 6BT, UK b Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial College, London SW7 2BP, UK article info Article history: Received 21 January 2014 Received in revised form 28 April 2014 Accepted 31 May 2014 Available online 9 June 2014 Keywords: Normal fault growth Fault kinematics Seismic reflection data Vertical seismic resolution Seismic forward modelling abstract Throw-depth profiles and expansion index plots are typically used to constrain the growth history of seismically imaged normal faults. However, the ability to accurately correlate displaced stratigraphic horizons across faults and hence constrain stratigraphic thickness changes is typically limited by the vertical resolution of, and noise within, the seismic reflection dataset. Vertical seismic resolution is a function of seismic velocities and the source wavelet frequency used during data collection. Here, we test how variations in source wavelet frequency and seismic noise influence imaging of normal faults, and our ability to determine the fault growth history from the construction of throw-depth profiles and expansion index plots. To achieve this, two input models were developed to mimic the geometry and growth history of polycyclic growth faults and blind normal faults. These models provided an input for a series of 2D seismic forward models from which we produced synthetic seismic profiles. The models were run at different peak frequencies and seismic noise levels, so as to mimic variations in seismic data quality associated with changes in the depth of burial. Throw-depth profiles and expansion index plots were derived from the synthetic seismic profiles and used to constrain the fault kinematics, and these results were compared to those derived from the input models. Our results indicate that, at lower peak frequencies and higher seismic noise levels, fault height can be underestimated, and strikingly, that the fault growth history can be misinterpreted. The results of our study indicate that geologists need to be aware of the imaging resolution of seismic reflection data when using these data to determine fault growth history of normal faults. Furthermore, hydrocarbon explorationists should be aware that seismic reflection data, the principal exploration tool, may not allow accurate determination of fault length and height, which may impact risking of hydrocarbon traps that require at least a component of fault seal. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Constraining the growth histories of normal faults Normal faults typically grow via one or a combination of the following two mechanisms: i) growth of a single fault via a sys- tematic increase in displacement, length and height (e.g., Watterson, 1986; Marrett and Allmendinger, 1991); and ii) growth as a result of along-strike or along-dip linkage of previously isolated fault segments (e.g. Segall and Pollard, 1980; Martel et al., 1988; Peacock and Sanderson, 1991; Mansfield and Cartwright, 1996; Pollard and Fletcher, 2005; Jackson and Rotevatn, 2013). To constrain the depth of nucleation and growth history of a normal fault using outcrop, seismic or model-derived data, two types of plots are constructed based on quantitative analyses of fault throw: i) throw versus depth plots, herein termed ‘T-z’ plots; and ii) expansion index plots (e.g. Thorsen, 1963; Bischke, 1994; Cartwright et al., 1998; Pochat et al., 2004, 2009; Hongxing and Anderson, 2007; Baudon and Cartwright, 2008a,b,c; Jackson and Rotevatn, 2013; Tvedt et al., 2013). In the case of an idealised blind isolated fault, the T-z profile will be symmetrical, with fault throw progressively and smoothly decreasing from a maximum at the fault centre to zero at the upper and lower tips (Kim and Sanderson, 2005); the site of fault nucleation is usually taken to correspond to the point of maximum throw on the T-z plot (Fig. 1) (e.g. Cartwright et al., 1998; Hongxing and Anderson, 2007). However, T-z and expansion index plots may also be influenced by factors such as variations in mechanical properties and/or lithology (e.g. Roche et al., 2012), tectonic reactivation and/or inversion (Mansfield and Cartwright, 1996; Cartwright et al., 1998; Hongxing and Anderson, 2007), and fault segment linkage (e.g. Kim and Sanderson, 2005; Jackson and Rotevatn, 2013; Tvedt et al., 2013). * Corresponding author. E-mail address: o.duffy@imperial.ac.uk (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.2014.05.021 0191-8141/© 2014 Elsevier Ltd. All rights reserved. Journal of Structural Geology 66 (2014) 382e399