Normal Fault Kinematics and the Role of Lateral Tip Retreat: An Example From Offshore NW Australia

Abstract

Understanding how normal faults grow is key to determining the tectono-stratigraphic evolution of rifts. 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, that is, does it abruptly die, or does the at-surface trace-length progressively shorten by so-called tip retreat? We, here, use a 3D seismic reflection data set 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 throw-length scaling relationship changes as a fault dies. We show that during the lengthening stage, which lasted <30% of the faults’ lives, 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’ lives, 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%. The results of our study may have broader implications for fault growth models, slip rate variability during fault growth, and the way in which faults die, in particular the role of lateral tip-retreat.