Bailey Lathrop, Frank Zwaan, Timothy Schmid, Christopher Aiden-Lee Jackson , Rebecca E. Bell, Atle Rotevatn, Guido Schreurs

Exploring how normal faults evolve is important for understanding the dynamic processes underlying the initiation and evolution of rift systems. Early-stage fault growth has been largely under-explored due to resolution limitations in seismic reflection data and the lack of three-dimensional exposures in the field. Physical analogue modelling offers a unique way to visualize and analyse early-stage fault growth. Here, we present results from an innovative analogue modelling approach that allows us to resolve fault growth in 4D through the use of a medical-grade, X-ray computed tomography (CT) scanner, as well as top-view time-lapse photography and digital image correlation (DIC) analysis.
We show that faults establish their vertical height at the earliest stage of deformation and laterally grow via a cyclical growth pattern, alternating between periods of rapid lengthening associated with relay-breaching and segment linkage, and periods characterised by throw accumulation. As extension continues, strain is partitioned onto increasingly fewer, optimally spaced and orientated faults, which continue to lengthen via segment linkage; faults in stress shadows, and/or with double conjugate boundaries, become inactive. It is the first time that fault lengthening and throw have been tracked in 4D with such high-fidelity and that this style of cyclical fault growth has been resolved, representing significant advances in our understanding of normal fault growth from segment-scale to network-scale, made possible only by the innovative use of X-ray CT-scanning.