Evolution of normal fault displacement and length as the continental lithosphere stretches

Continental rifting is accommodated by the development of normal fault arrays. Fault growth patterns control their related seismic hazards, as well as influencing the tectonostratigraphic evolution, resource extraction and CO2 storage potential of rifts. Our understanding of fault evolution is largely derived by observing the final geometry and displacement (D)-length (L) characteristics of active and inactive fault systems, and by making subsequent inferences on their kinematics. We rarely consider how these properties change through time, and how the growth of individual fault systems relates to the temporal evolution of their host arrays. Here we use 3D seismic reflection and borehole data from the Exmouth Plateau, NW Shelf, Australia to determine the growth of rift-related, crustal-scale fault systems and arrays over geological timescales (10^6 Ma). The excellent-quality seismic data allows us to reconstruct the entire Jurassic-to-Early Cretaceous fault array over a large area (~1200 km2). We find that fault trace lengths were established early, within the first ~7.2 Myr (8%) of rifting, and that along-strike migration of throw maxima towards the centre of individual fault systems occurred after ~28.5 Myr (33%) of rifting. We propose that D and L may scale linearly, but increase via alternating phases of fault lengthening and displacement accumulation. Growth trajectories produce inflections in D-L space, reflecting times when fault lengths and/or displacement saturate a given rock volume, possibly controlled by crustal thickness. At the array-scale, faults located in stress shadows become inactive and appear under-displaced relative to adjacent larger faults, onto which strain localises as rifting proceeds. This implies that the scatter frequently observed in D-L plots can simply reflect fault growth and array maturity. We show that by studying complete rift-related normal arrays rather than individual faults, we can better understand how faults grow and more generally how continental lithosphere deforms as it stretches.