Hydrothermal fluids and where to find them: Using seismic attenuation and anisotropy to map fluids beneath Uturuncu volcano, Bolivia

Abstract

Fluids are present in much of Earth's crust. Mapping where and why these fluids accumulate, as well as identifying their composition are critical questions in the earth sciences. For example, understanding where magma resides is important for volcanic hazard assessment, mapping the extent of geothermal systems is pertinent for maximizing production efficiency, and identifying the location and properties of metal-rich brines is relevant for mineral exploration. The question that this study addresses is: can seismic attenuation combined with seismic anisotropy be used to map the location of fluids and, in combination with auxiliary data, identify fluid composition? Here, we test this hypothesis at Uturuncu volcano, Bolivia.Uturuncu volcano sits within the Bolivian Andes. The volcano last erupted 250,000 yr ago (Muir et al., 2015), yet has exhibited significant uplift at rates of up to 1 cm/yr (Gottsmann et al., 2018;Pritchard et al., 2018). Uturuncu lies ∼20 km above the Altiplano-Puna Magma (or Mush) Body (APMB), Earth's largest body of silicic partial melt (Pritchard et al., 2018). This melt heats the crust above and potentially provides a source of ascending metalrich volatiles (Blundy et al., 2021). Uturuncu provides an ideal location for attempting to image and identify fluids, since the host crust isolated from the volcanic system is likely predominantly unsaturated except near surface rivers/lakes, while a shallow, partially saturated hydrothermal system likely exists under the volcano that is sustained via heat and volatiles from the APMB (Gottsmann et al., 2022).

Hydrothermal Fluids and Where to Find Them: Using Seismic Attenuation and Anisotropy to Map Fluids Beneath Uturuncu Volcano, Bolivia

“…All the seismic data used in this study are available on the publicly accessible IRIS data repository (YS and XP network codes [see Pritchard, 2009;West & Christensen, 2010]) (https://ds.iris.edu/ds/nodes/dmc/). The earthquake catalog used is detailed in Hudson et al (2022) and the gridded tomography data are available on Zenodo (Hudson, 2023b). The software used to measure path-average attenuation for each earthquake is SeisSrc-Moment (Hudson, 2020), available open source.…”