Friday seminars of Institute of Earth Sciences, October 23th 2026 - Andy Nowacki (University of Leeds)

Abstract

Corbetti in Ethiopia is a silicic rift volcanic system where a 150 MWe geothermal power plant is planned. It is suspected from mapping, seismicity, remote geodesy (interferometric synthetic aperture radar; InSAR) and geoelectrical (magnetotelluric; MT) surveys that cross-rift faulting has led to a north–south compartmentalisation of the geothermal resource. However, how this is represented in the elastic structure is uncertain. Likewise, there is uncertainty in the nature of the deeper heat source at Corbetti. MT and InSAR also suggest that a region of high melt content is present, but estimates of its depth and likely responsibility for surface uplift do not closely agree. In this study, therefore, we seek to test these hypotheses of the presence of melt and compartmentalisation in the geothermal reservoir by comparison with seismic data. We use an existing catalogue of earthquakes and a Bayesian probabilistic approach to build an ensemble of millions of tomographic models of S-wave speeds in the subsurface below Corbetti down to ~15 km below sea level. This ensemble represents the probability of any given seismic velocity being present at each point in space. This probabilistic approach is necessary: firstly, data coverage is limited, and in this way we can obtain the uncertainty in the model everywhere; and secondly, we are able to use the probabilities we obtain to statistically test whether any existing hypothesis are supported by the seismic data. We find that the seismic evidence does not support the idea that there is a deep-seated (>2 km depth) separation between the north and south of the caldera, as suggested by InSAR, but it does weakly support the presence of a magma region at ~5 km depth. These results can be used in a risk-based framework to make future decisions on exploration at Corbetti and the work repeated at other sites worldwide.

All are welcome.