Kenya Rift Valley Break-up – Focus on Velocity, Trend, and Vertical Displacement

Abstract

Position time series files processed by GAMIT/GLOBK with extension velocities in the Victoria-Nubia reference frame processed by the rot program from thirteen continuous Global Navigation Satellite System (GNSS) station along the East African Rift System (EARS) from 2017 to 2021 were used to constrain plate tectonic motion to observe the Kenya rift extension rates between the Victoria microplate and the Somalian plate. These position time series files for the GNSS stations close to the major lakes along the Kenyan Rift Valley were also used to compare monthly rainfall averages from nine rainfall stations close to the GNSS stations. The GNSS stations in the Northern Kenyan Rift (NKR) showed slower extension rates with XTBI and XTBT measuring 0.8mm/yr and 2.1mm/yr velocity break-up rates respectively. On the other hand, the Central Kenyan Rift (CKR) GNSS stations showed faster extension rates with KYN6, KYN4, KYN3, KYN2, and KYN7 measuring 1.7mm/yr, 1.5mm/yr, 3.0mm/yr, 2.0mm/yr, and 3.3mm/yr velocity break-up rates respectively. The GNSS stations in the NKR show slower geodetic rifting rates unlike the GNSS stations in the CKR. The difference in the break-up velocity rates could be possibly due to the influence of Gravitational Potential Energy (GPE) that is higher in the CKR due to high topography, unlike the NKR, which is generally a depression, thus having lower GPE. The position time series also recorded surface amplitude change that portray an inverse relationship with rainfall time series. Thus, this inverse relationship shows a systematic correlation between vertical displacements portrayed by crustal subsidence and continental water loading (CWL), where increase in rainfall leads to crustal subsidence, and little or no rainfall leads to crustal flexure. Key Words: East African Rift System, Kenya Rift Extension Rates, Vertical Displacement, Gravitational Potential Energy, and Continental Water Loading.