The magmatic plumbing system of the Acoculco volcanic complex (Mexico) revealed by ambient noise tomography

Abstract

The GEMex project is a Mexican-European cooperation in geothermal energy focusing on enhancing the Acoculco geothermal system. The volcanic system belongs to the northeastern part of the Trans-Mexican Volcanic Belt. In this study, we present ambient noise seismic tomographies of the anisotropic shear wave velocities and reveal the magmatic plumbing system. The tomographies result from the joint inversion of the multi-mode Rayleigh and Love surface wave velocities and Horizontal to Vertical Spectral Ratios (HVSR or H/V). We also discuss the advantage of this technique compared to traditional ambient noise tomography methods and underline the importance of considering multiple surface wave modes to correctly reveal velocity anomalies buried a few kilometers in depth. A reservoir is identified at about 5 km depth at the northeast outside of the caldera. This reservoir is linked to the south caldera surface via a conduit that follows the caldera's eastern border, mainly the Chignahuapan graben. An intermediate reservoir is also observed at about 2.5 km depth, just below the three most recent monogenetic volcanoes. Results agree well with geological studies, the caldera collapse, its temporal evolution, and other geophysical studies recently reported.