Seismicity East of The Southern Kenya Rift Valley, Kenya

Abstract

A new seismicity map that accounts for the seismic behavior, tectonic complexity, and potential seismic hazards in the eastern part of the southern Kenya Rift Valley is presented. The results are based on the analysis of 224 earthquakes recorded for 103 years, from 1917 to 2020, with magnitudes ranging from 2.5 to 5.6 Mw, confirming moderate to high seismicity and subsequently moderate to high-stress levels. Data from fifteen catalogs is collated and homogenized; magnitudes are unified to Mw. The seismicity is diffuse with pockets of seismic clustering, delineating seven seismic zones, namely the Simba-Mutito zone, Oloitokitok-Kimana-Chyulu zone, Mzima Springs-Mashetani Lavas zone, the Yatta-Voi zone, the Tertiary-Quaternary sediments (north) zone, the Tertiary-Quaternary sediment (south) zone, and the Mwananyamala-Davie fracture zone. Seismicity does not sorely straddle the surface faults; this is attributed to the reactivation of buried faults oriented northwest-southeast, north-south, and northeast-southwest. Further, the study infers an east-west trending shear zone running from the Mzima Springs and across the Yatta shear zones to the coastal sediments. We affirm that the seismicity is not confined to the Southern Kenya Rift but extends off the rift eastwards, re-emphasizing the need for comprehensive seismic monitoring and hazard assessment beyond the main rift zones.