Abstract
A Magnetotelluric reconnaissance survey of 39 soundings was carried out in the caldera of Nisyros, a small island volcano at the eastern end of the Hellenic Volcanic Arc (HVA), Greece, in an attempt to explore the high temperature geothermal resource of the area. Iteratively reweighted least squares was implemented to compute stable and smooth Earth response functions exhibiting 2-D to weakly 3-D attributes, as a result of induction in low-contrast local geoelectric inhomogeneities, superimposed on a dominantly 2-D background structure; coastal and island induction effects are absent due to the low offshore/onshore resistivity contrast at, and below sea level. Application of advanced hypothetical event analysis techniques to study the spatial properties of the telluric field demonstrated that convection and hydrothermal circulation is controlled by a system of antithetic NE-SW oriented active normal faults which form a graben-like structure and define the 2-D background, as well as a conjugate system of NNW-SSE normal faults which is particularly active at the SW quadrant of the island and define the main convection path. It was determined that under these conditions the data could be interpreted with 2-D inversion, which has successfully reconstructed detailed images of the structural and functional elements of the hydrothermal system. The structural elements include a number of shallow hot water reservoirs in the argillic and phyllic alteration zones and a laterally extended deep (approx. 1 km) circulation zone, all embedded in a low-resistivity with very low lateral contrasts. The functional elements include images of the most important convection conduits created by the intersection of major fault planes. The results are corroborated by the logs of two deep exploration wells. Overall, on the basis of a carefully reworked data set, our analysis has provided detailed images of the volcano’s interior and valuable insight into its structure, function and geothermal potential.
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Tzanis, A., Sakkas, V., Lagios, E. (2018). Magnetotelluric Reconnaissance of the Nisyros Caldera and Geothermal Resource (Greece). In: Dietrich, V., Lagios, E. (eds) Nisyros Volcano. Active Volcanoes of the World. Springer, Cham. https://doi.org/10.1007/978-3-319-55460-0_6
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