Degassing mechanism change regarding an eruption in 2009 at Mt. Asama revealed by volcanic gas and seismic studies
Abstract
Volcanic gas has a close relationship with geophysical phenomena involving eruptive activities. In particular, previous studies suggested that very-long-period (VLP) seismic signals are caused by fluid (i.e., gas and/or magma) within a volcano (e.g., Chouet et al. 2010). Investigation for VLP seismic source is crucial not only for volcanic seismology but also for understanding degassing processes at depths. In this study, at Mt. Asama, Japan, we examine VLP seismic source model of the volcano and change of degassing mechanism before and after an eruption in Feb. 2009 by means of a linkage between volcanic sulfur dioxide emission and VLP seismic moment, which was revealed by Kazahaya et al. (2011). This linear relationship between them implies that volcanic gas injected into the VLP seismic source causes a VLP pulse. Complementing it with volcanic gas composition data, we calculated pressure/volumetric changes at the VLP seismic source both by volcanic gas amount and by seismic analyses; and found a significant difference between them. We propose the VLP seismic source filled with pressure (porous) medium so as to explain this discrepancy. This linear relation between volcanic gas and VLP seismic signal allows us to calculate gas amount triggering VLP pulses from seismic record. The long-term time series of volcanic gas emission which gives rise to VLP pulses were examined; the ratio of gas emission regarding VLP pulses showed drastic change before and after the eruption in Feb. 2009. The novel timeline data suggest that degassing mechanism at the depth within the volcano changed by the eruption to excite VLP seismicity easier. GPS and infrasonic data may give constraints to comprehend the volcanic structure such as magma supply and gas exhalation, respectively. Collaboration of geochemical and geophysical studies opens up the possibility to get brand new insights within the volcano.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V53B2827K
- Keywords:
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- 7280 SEISMOLOGY / Volcano seismology;
- 8400 VOLCANOLOGY;
- 8414 VOLCANOLOGY / Eruption mechanisms and flow emplacement;
- 8430 VOLCANOLOGY / Volcanic gases