Bailey Lathrop, Christopher Aiden-Lee Jackson , Rebecca E. Bell, Atle Rotevatn

Understanding how normal faults grow is key to determining the tectono-stratigraphic evolution of rifts, and the distribution and size of potentially hazardous earthquakes. According to recent studies, normal faults tend to grow in two temporally distinct stages: a lengthening stage, followed by a throw/displacement accumulation stage. However, this model is still debated and not widely supported by many additional studies. Relatively few studies have investigated what happens to a fault as it becomes inactive, i.e. does it abruptly die, or does its at-surface trace-length progressively shorten by so-called tip retreat? We here use a 3D seismic reflection dataset from the Exmouth Plateau, offshore Australia to develop a three-stage fault growth model for seven normal faults of various sizes, and to show how the displacement-length scaling relationship changes as a fault dies. We show that during the lengthening stage, which lasted <30% of the faults life, faults reached their near-maximum lengths, yet accumulated only 10-20% of their total throw. During the throw/displacement accumulation stage, which accounts for c. 30-75% of the faults life, throw continued to accumulate along the entire length of the faults. All of the studied faults also underwent a stage of lateral tip-retreat (last c. 25% of the faults lives), where the active at-surface trace-length decreased by up to 25%. This work has implications for our understanding of the temporal evolution of normal faults, in particular how they grow and how they die, with the final stage of tip retreat typically being absent from more fault growth models.