Interconnectivity of Magmatic and Hydrothermal Systems of Aluto Volcano
in the Main Ethiopian Rift inferred from Seismicity
Abstract
Aluto volcano, situated in the central Main Ethiopian Rift (MER) within
the northern part of the East African Rift System (EARS) is seismically
active, with indications of unrest detected by InSAR. It hosts
Ethiopia’s first pilot project for geothermal energy. Despite extensive
studies, uncertainties remain about the mechanisms of unrest and the
existence of a shallow magma chamber beneath Aluto which could drive the
hydrothermal system, and is crucial for understanding its geothermal
potential. This study investigates Aluto’s magmatic and hydrothermal
systems using observations of seismicity in the region. We analyse
seismic data from January 2012 to January 2014, locating 2393 events,
which lie predominantly along the Wonji Fault Belt (WFB). Event depths
reach up to 40 km beneath Aluto, suggesting the presence of fluids and
perhaps a highly crystallised mush, consistent with prior
magnetotelluric and gravity studies. Deep crustal seismicity likely
relates to fluid and/or magmatic processes. High-b value of 1.97 ± 0.10
at Aluto indicates the presence of fluids. Seismicity is negligible
beneath Silti Debre Zeyt Fault Zone (SDFZ), previously identified as a
highly conductive, indicative of melt. Focal mechanisms show normal
faulting in the direction of rift extension and full-moment tensor
inversions suggest shear-failure with fluids potentially activating
existing faults. We suggest that the magmatic and hydrothermal systems
are connected through pre-existing faults. Understanding this
interaction will enhance our knowledge of the geothermal system,
volcanic risk, mechanisms of unrest, and emplacement of geothermal
brines.