Seismic Absorption and Scattering Imaging at Aluto Volcano in the Main Ethiopian Rift

Understanding the distribution of fluids in subsurface reservoirs within volcanic systems is important for geothermal energy development, the exploration of critical-metal-bearing brines, and other applications, including forecasting volcanic eruptions. Seismic attenuation tomography can be used to map fluids and structural features beneath a volcano. Here, we use coda wave attenuation and peak delay time, which measure absorption and scattering, respectively, at the Aluto volcano. Aluto volcano is located in the central part of the Main Ethiopian Rift (MER) and is Ethiopia’s first pilot site for geothermal exploration. Absorption is highly effective in detecting fluids, high temperatures, and melt, while scattering is effective in detecting lithological variations and structural features such as faults and fracture systems. We analysed seismic data from January 2012 to January 2014, locating 2,393 events that predominantly lie along the Wonji Fault Belt (WFB) using non-linear location methods. We selected 312 events for 3D attenuation tomography based on the number of phases and a coda-to-noise ratio of three or higher. High inverse coda quality factor is spatially correlated with high-temperature areas, zones with hydrothermal manifestations and elevated CO₂ flux, and around productive geothermal wells with high temperature and high enthalpy. High scattering is spatially correlated with areas of structural features such as faults and fracture systems, which act as fluid pathways and with the most permeable geothermal wells. These methods better constrain the distribution of fluids, high-temperature areas, and lithological and structural variations and can be used in geothermal exploration. High absorption and scattering areas are ideal for geothermal exploration, as they indicate hot fluids in fractured permeable rock.