GNSS and InSAR observations at the Olkaria geothermal site in the central Kenya Rift System

The Quaternary Olkaria volcanic complex is a high-temperature geothermal system in the Central Kenya Rift located in a structural transition zone between the Mt. Longonot and Mt. Eburru eruptive centers. This region is subject to protracted crustal deformation and ground subsidence. Vertical ground motion is associated with crustal-scale processes, including magmatic intrusion and eruption, as well as normal and transfer faulting. In addition, the region has been the subject of fluid extraction associated with geothermal energy production. In the past 20 years, increased re-injection strategies were implemented in order to slow down drawdown and thereby mitigate against exponential ground subsidence. Although an extensive benchmark network for monitoring surface deformation was established in 1983, the lack of subsequent precise leveling surveys has necessitated the use of state-of-the-art geodetic techniques to quantify the magnitude and temporal evolution of ground deformation to better understand the roles of tectonic and anthropogenically induced land-surface changes.

Here we present new radar interferometry observations spanning the past decade, combining Sentinel-1 data (2016–2026) and TerraSAR-X data (2024–2026), to constrain vertical surface motion at high spatial and temporal resolution. These InSAR time series are complemented by measurements from a local GNSS network installed on and around the Olkaria dome. Our results show that rapid subsidence observed since 2016 slowed markedly around 2020 and has since largely stagnated. High-resolution X-band and persistent scatterer C-band data reveal that localized subsidence persists near fluid-extraction sites, whereas regional subsidence rates in the area of the volcanic complex have decreased by approximately an order of magnitude. Independent, statistically robust GNSS time-series analyses support these observations. We further assess different InSAR processing strategies and highlight the critical importance of rigorous atmospheric correction due to the influence of high seasonal moisture availability.

Overall, our analysis indicates that vertical land-surface deformation in the Olkaria region at annual timescales is primarily driven by deep-seated magmatic processes, while geothermal energy production has only contributed to localized subsidence through fluid extraction.