Decomposition, location, and persistence of seismic signals recovered from continuous tremor at Erta ʹAle, Ethiopia

Subband decomposition and reconstruction (SDR) provides a quantitative, semi-automated, rapid means of analyzing volcanic tremor, which can recover signals that dominate different parts of the frequency spectrum while preserving polarization and phase. Here, applied to data from a two week experiment at Erta ʹAle in Nov–Dec 2003, we demonstrate that the SDR method can identify signals corresponding to source processes active in several different physical regions of the Erta ʹAle caldera. Different recovered signals suggest that the continuous tremor at Erta ʹAle is a composite of several seismic sources, including conduit resonance, bubble bursting phenomena, and degassing at fumaroles. These signals are seen throughout the 2003 experiment, suggesting that several competing source models of volcanic tremor can produce signals at the same volcanic conduit system simultaneously.