Source Mechanism of Volcanic Explosions Investigated by Seismo-Acoustic Observations

Source mechanisms of explosive, volcanic eruptions are critical for understanding magmatic plumbing systems, determining the evolution and geometry of source regions, and assessing eruptive behavior as well as hazard impact. In the last two decades, volcano seismo-infrasonic observations have become an essential part of volcano monitoring systems. Because the open vent of a volcano is a corridor connecting the solid earth to the atmosphere, explosive eruptions efficiently excite both infrasound and seismic waves. Each of these mechanical waves includes characteristic information on several stages of the eruption process, and the coupling of these processes sheds considerable light into volcano dynamics. In this dissertation, details of the explosive eruption mechanism are investigated by seismo-acoustic observations at two volcanoes: Karymsky Volcano in Kamchatka, Russia, and Tungurahua Volcano, Ecuador. First, path effects of infrasound waves near volcanic craters are investigated as they pass the rim of the vent and propagate to remote stations. Next, characteristics of infrasonic sources excited by volcanic explosion are explored. Distortion due to diffraction and reflection of infrasound at the crater vent is shown to be significant and must be accounted for when interpreting explosion source physics from wave fields. To address these problems we propose an acoustic, multipole source model in a half-space for volcanic explosions. Acoustic observations at Tungurahua Volcano appear to corroborate this model. Finally, source mechanisms of explosive eruptions at Tungurahua are investigated by jointly analyzing infrasound and seismic waves. Using this approach, the time evolution and geometric orientation of the magmatic plumbing system, during a period of volcanic crises at Tungurahua, are illuminated and explained.Doctor of Philosoph