TITLE:
Resistivity Structure of the Korosi Geothermal Field, Kenya, from Three Dimensional Magnetotelluric Inversion
AUTHORS:
Claire Kimeli, Justus Maithya, Josphat Mulwa, John Githiri, Isaac Kanda
KEYWORDS:
Korosi Geothermal Field, Magnetotelluric, 3D Inversion, Resistivity, Kenya Rift
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.14 No.8,
August
20,
2026
ABSTRACT: The Magnetotelluric (MT) method is widely used to image subsurface electrical resistivity and characterize geothermal systems at depth. In this study, 81 MT soundings were analyzed to assess the geothermal resource and map the subsurface resistivity distribution of the Korosi geothermal field within the Kenya rift. Phase tensor analysis of the impedance data showed that skew angles and ellipticity increase with period, pointing to a largely three-dimensional (3D) resistivity distribution beneath the geothermal field. Consequently, the full impedance tensor was inverted using the ModEM three-dimensional inversion code. The recovered model, examined along three west-east profiles, reveals a broadly consistent three-layer resistivity structure. It comprises a thin near surface resistive layer (>100 Ωm) interpreted as relatively dry or weakly altered volcanic rocks, an extensive conductive zone (100 Ωm) that may represent higher temperature alteration zones, dense intrusive rocks or low-porosity volcanic units. The conductive anomalies vary considerably in thickness and lateral continuity across the field. Western conductors extend toward the Nakaporon fault zone, whereas eastern conductors occur toward the Nagoreti area. These conductive zones are locally separated by relatively resistive domains, suggesting that hydrothermal alteration is not uniformly distributed beneath the Korosi volcanic complex. The spatial relationship between the conductive anomalies and mapped faults suggests that these structures may influence fluid circulation, alteration patterns and compartmentalization of the geothermal system.