Source mechanisms of vulcanian eruptions at Mt. Asama, Japan, inferred from volcano seismic signals
Published:January 01, 2008
Takao Ohminato, 2008. "Source mechanisms of vulcanian eruptions at Mt. Asama, Japan, inferred from volcano seismic signals", Fluid Motions in Volcanic Conduits: A Source of Seismic and Acoustic Signals, S. J. Lane, J. S. Gilbert
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During the 2004 Asama volcanic activity, five summit eruptions, accompanied by the broadband seismic signals, were observed. We re-analyse the broadband waveform data analysed by Ohminato et al. (2006) using relaxed restrictions. The results are essentially the same as those shown in the previous study. The results of the waveform inversions that assume a point source show that the force system is dominated by vertical single-force components. The source depths with dominant single-force components are 200–300 m beneath the summit crater. In the source-time history of the vertical single-force component, two downward forces separated by an upward force lasting for 5–6 s are clearly seen. We conduct a grid search for the best combination of two point sources, each consisting of a single-force component. The best waveform-match solution was obtained when one of them is positioned near the top of the conduit, and the other source is positioned 2000 m below the upper source. When a combination of single-force and moment-tensor components is assumed for the two-point source model, the moment source is located out of the vertical hypocentre distribution, suggesting a steeply inclined conduit.
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Fluid Motions in Volcanic Conduits: A Source of Seismic and Acoustic Signals
Volcanoes become active when fluids are in motion, and erupt when these fluids escape into the atmosphere. Volcanic fluids are a mixture of solid, liquid and gas. These mixtures result in a complex range of flow behaviour, especially during interaction with conduit geometry. These processes are not directly observable and must be inferred from interpretations of field observation and measurement. One of the outcomes of this complexity is the generation of pressure and force transients as high-density phases accelerate and decelerate during unsteady flow. These transients are one means of flexing the conduit wall, a process that manifests itself as ground motion and is detectable as volcano seismic signals. On eruption, volcanic fluids interact with the atmosphere and generate acoustic and thermal signals. In this Special Publication we present a series of papers based on field, numerical and experimental approaches that seek to establish links between geophysical signals and fluid motion in volcanic conduits.