Investigation of Rift Evolution Through Examining Scaling Properties of Fault Populations Within the Central Kenya Rift

Abstract

Fault scaling relations for three different fault populations within the central Kenya rift have been quantitatively analysed and compared in order to characterize the behaviour of fault growth and distribution of strain accommodation, and therefore inform our understanding of the evolution of this part of the rift. 500 surface faults were mapped from digital Elevation Model data, and three fault population zones (zone1, zone2& zone3) were defined based upon their average fault orientations as NNE, NNE to NNW and NNW respectively. Estimations of extensional strain obtained from three different methods revealed a general increase of strain from the south to the north. Relationship between fault lengths and their throws for the picked faults fit reasonably to a power-law distribution. Fault length populations in the three zones showed similar power-law exponent, hence fault throw populations were used to examine deformation in this region. the Power-law exponents for throw populations in the three zones decrease with increasing strain, which implies that the strain is increasingly localised onto larger faults as the fault system becomes more evolved as we move from south to north along the rift, this decrease of power law exponent could indicate different stages of fault evolution, which may suggest that faults in zone3 in the south are in a less mature stage of growth than zone2 faults in the centre, and zone2 fault population is in a less developed phase of growth than faults in zone1 in the northern part of the study area. Analysis of the spatial distribution of fault throw populations exhibits three domains of deformation in the three zones; distributed faulting in zone3 and localized faulting deformation in zone1, with the transition between the two occurs in zone2. Isolated faults in zone3 seemed larger in displacement comparing to that of zone2 but fault trace length appear to be to some extent comparable in the two zones, which may suggest a rapid propagation of fault length at an early stage of fault growth. The results showed that this part of the central Kenya rift displays a range of variations, not only in fault orientation, but also in the total amount of strain, strain accommodation and fault evolution along the axis of the rift. These results also underline that the processes of progressive fault system maturity and strain localization onto large faults could occur even at relatively small scale of fault populations within the rift system.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017