Normal fault growth in continental rifting: Insights from changes in displacement and length fault populations due to increasing extension in the Central Kenya Rift

This study examines the scaling relationship between fault length and displacement for the purpose of gaining a better understanding of the evolution of normal faults within the central Kenya Rift. 620 normal faults were manually mapped from a digital elevation model (DEM), with 30 m2 resolution and an estimated maximum displacement of ~40–~6030 m and fault lengths of 1270 ‐ 60,600 m. To assess the contribution of fault populations to the strain accommodation from south to north, the study area has been divided into three zones of fault populations based upon their average fault orientations; zone 1 in the north is dominated by NNE striking faults, zone 2 in the centre of the rift is characterised by NNW to NNE fault trends, whereas zone 3 in the south is characterised by NNW striking fault systems. Extensional strain was estimated by summing fault heaves across six transects along the rift, which showed a progressive increase of strain from south to north. The fault length and displacement data in the three zones fit to a power law distribution. The cumulative distributions of fault length populations showed similar fractal dimension (D) in the three zones. The cumulative displacement distributions for the three zones showed a decrease in the Power-law fractal dimension with increasing strain, which implies that the strain is increasingly localized onto larger faults as the fault system becomes more evolved from south to north. Increasing displacement with increasing strain while the fault length remains almost constant may indicate that the fault system could be evolving in accordance with a constant length fault growth model, where faults lengthen quickly and then accrue displacement. Results of this study suggest that the process of progressively increasing fault system maturity and strain localization onto large faults can be observed even over a relatively small area (240 × 150 km) within the rift system. It is also suggested that patterns of fault growth can be deduced from the fractal dimension of cumulative distribution of fault size populations.