Characterization of 3D fault structures in the Paka geothermal field using TDR and HGM filters on Bouguer gravity data: Implications for geothermal fluid flow dynamics in the northern Kenya Rift

Abstract

Gravity data from the Paka geothermal field in the northern Kenya Rift were analysed using tilt derivative (TDR) and horizontal gradient magnitude (HGM) methods, along with 3D modelling via the VOXI Earth Modelling tool, with the aim to characterize subsurface fault structures. Understanding these faults is crucial for characterising their trends, distribution, depths, and their influence on geothermal fluid flow. The TDR and HGM procedures were applied to Bouguer gravity data, while 3D structural analysis was performed using the VOXI Earth Modelling tool within the Geosoft Oasis software. The results reveal that most local fault structures trend in NW–SE and N–S directions, aligning with regional tectonic structural patterns. The tilt depth technique (TDT) estimated the depths of these local faults to range from 0 to 1500 m. A dome-shaped fault structure, that is connected to the caldera ring fault and underlying magma chamber, was identified at depths of 1–4 km. Additionally, a deeper rift-related fault structure trending N–S was observed at depths of 2–5 km. These features were delineated using HGM, TDR, and 3D inversion analysis. The 3D inversion results suggest that most fault structures dip steeply, approximately 90 $°$, with some showing slight vertical tilts. These faults play a critical role in controlling the movement of geothermal fluids within the Paka volcanic complex. The volcano is characterized by interconnected vertical faults trending NW and extending from the surface down to about 5000 m. Given that geothermal resources in this area are structurally controlled, the identified faults are likely to serve as key conduits or hosts for geothermal fluids.