Strain localisation and population changes during fault system growth within the Inner Moray Firth, Northern North Sea

Abstract The evolution of fault populations is established for an area within the Late Jurassic Inner Moray Firth sub-basin of the North Sea. Sedimentation rates outstripped fault displacement rates resulting in the blanketing of fault scarps and the preservation of fault displacement histories. Displacement backstripping is used to establish the growth history of the fault system. Fault system evolution is characterised by early generation of the main fault pattern and progressive localisation of strain onto larger faults. This localisation is accompanied by the death of smaller faults and an associated change in the active fault population from power-law to scale-bound. Fault length populations evolve from a power-law frequency distribution containing all faults, to a power-law distribution with a marked non-power-law tail containing the largest faults. This change in population character is synchronous with the development of a fully-connected fault system extending across the mapped area and the accommodation of displacements almost exclusively on the largest faults. Strain localisation onto fewer and better connected faults represents the most efficient means of accommodating fault-related deformation and is considered to be a fundamental characteristic of the spatio-temporal evolution of fault systems. Progressive strain localisation requires complementary changes in the characteristics of associated earthquake populations.