| 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 and geoelectrical surveys that cross-rift faulting has led to compartmentalization 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. Magnetotelluric and interferometric synthetic-aperture radar observations agree 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 present hypotheses of the presence of melt and effect of fractures on the geothermal reservoir by comparison with seismic data. We use a catalogue of earthquakes and a Bayesian probabilistic approach to build an ensemble of millions of tomographic models of P- and 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—such as differing elastic parameters across a known fault—are supported by the seismic data. We present our results and interpret them in terms of the current state of the Corbetti geothermal system. |