Combined Multi-Scale Inversion of Regional and Local Magnetotelluric Data from the Main Ethiopian Rift

Abstract:

Ethiopia aims to overcome energy poverty by increasing renewable energy generation and is increasing its efforts to expand geothermal energy extraction. High geothermal energy potential in Ethiopia is linked to the Main Ethiopian Rift (MER) and its abundant magmatism. Therefore, a better understanding of magma distribution in the MER is an important factor for successful geothermal power plant development. The magmatic-hydrothermal system of the only producing geothermal field at the dormant volcano Aluto was only recently imaged by a high-resolution magnetotelluric (MT) survey by ETH Zürich and the Geological Survey of Ethiopia (GSE). The question was raised if Aluto’s magmatic plumbing system might have a common deep-rooted source with an off-rift axis magmatic system in the Silti-Debre Zeyit Fault Zone (SDFZ), which was imaged by the first regional 2D MT cross rift profile from the RiftVolc project.

The aim of this study is to investigate the relation of these magmatic systems by combining the two existing MT datasets. The regional 2D cross rift dataset (RiftVolc project) consists of 27 stations along a 120 km profile and the high-resolution local dataset (ETH Zürich, GSE) consists of a selection from more than 200 sites that were installed on Aluto. We combine the regional profile data with a subset of profile-aligned stations from the local Aluto dataset, in order to obtain a multiscale 2D model with higher resolution below Aluto. For inverse modelling we use a novel FEM code (GoFEM) that allows for accurate incorporation of topography and uses frequency-dependent automatic mesh refinement techniques.

This study aims to gain new insights into the deeper magmatic plumbing system below Aluto that were so far limited by the sparse site distribution of the regional profile and the limited aperture of the local dataset from Aluto. Our goal is to provide an improved understanding of the deep distribution of melt in this part of the MER and how it connects to the shallow magmatic system of Aluto. This knowledge is crucial to assess possible reactivation of the volcanoes magma reservoir, which is crucial for risk assessment and geothermal energy generation at the geothermal power plant located on Aluto.