Determination of anthropologically induced deformation along the Kenyan Rift system using Multitemporal InSAR analysis with Sentinel-1 data.

Abstract

The Kenyan Rift system hosts various forms of land use, including residential, commercial, and agricultural. In addition, the geology of the Kenyan Rift, the geodynamic setting of the quaternary volcanoes along the rift axis, and the high temperatures associated with the hot asthenosphere along the Kenyan Rift system are favourable for the occurrence of geothermal fields, some of which have already been harnessed for the generation of electricity. The interplay of human activities along the Kenyan Rift system can cause deformation, which is also prone to deformation due to geophysical activities such as volcanism and magmatism. In our study, we utilized both conventional and optimized multitemporal InSAR analyses based on the SBAS method to quantify human-induced deformation along the Kenyan Rift. By directly estimating the tropospheric delay from Sentinel-1 SAR data, the optimized approach can reduce errors in InSAR derived displacement measurements. Nairobi, located on the eastern flank of the Kenyan Rift, has experienced significant deformation caused by urbanization and the overexploitation of groundwater. A maximum subsidence rate of approximately 55 mm/yr. was observed in one of the eight deformation units that are mainly located in residential areas. Njoro town and Nakuru town industrial zone have also been shown to be undergoing land subsidence of approximately 20 mm/yr. and 10 mm/yr., respectively, both of which are associated with the overexploitation of groundwater resources. In addition, land subsidence in the range of 20 mm/yr was observed at several flower farms in Naivasha, which can also be attributed to the overexploitation of groundwater. At Olkaria, we observed land subsidence in the seven geothermal fields in the range of 22-50 mm/yr., we also observed at Menengai Crater Land subsidence and uplift of approximately 8 mm/yr. and 6 mm/yr. respectively. There is a significant deformation in the Kenyan Rift as a result of human activities, and these results indicate that InSAR can be used to monitor deformation in regions that were previously unmonitored due to the associated costs of using other geodetic monitoring techniques. Similarly, correct estimation of tropospheric delay in InSAR not only leads to better time-series displacement estimation with a more apparent temporal trend but also reveals subtle deforming regions that are otherwise obscured by tropospheric delay in the conventional method.