Bridging Spatiotemporal Scales of Normal Fault Growth During Continental Extension Using High-Resolution 3D Numerical Models

Sophie Pan , John Naliboff, Rebecca E. Bell, Christopher Aiden-Lee Jackson 

Continental extension is accommodated by the development of kilometre-scale normal faults, which grow during metre-scale slip events that occur over millions of years. However, reconstructing the entire lifespan of a fault remains challenging due to a lack of observational data with spatiotemporal scales that span the early stage (<10^6 yrs) of fault growth. Using 3D numerical simulations of continental extension and novel methods for extracting the locations of faults, we quantitatively examine the key factors controlling the growth of rift-scale fault networks over 10^4-10^6 yrs. Early-formed faults (<100 kyrs from initiation) exhibit scaling ratios consistent with those characterising individual earthquake ruptures, before evolving to be geometrically and kinematically similar to more mature structures developed in natural fault networks. While finite fault lengths are rapidly established (<100 kyrs), active deformation is transient, migrating both along- and across-strike. Competing stress interactions determine the distribution of active strain, which oscillates locally between being localised and highly distributed. Higher rates of extension (10 mm yr-1) lead to more prominent stress redistributions through time, promoting episodic localised slip events. Our findings demonstrate that normal fault growth and the related occurrence of cumulative slip is more complex than that currently inferred from displacement patterns on now-inactive structures, which only provide a spatial- and time-averaged picture of fault kinematics and related geohazard.