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[SVC29-07] Temporal changes in volcanic seismicity before eruptions based on the generic volcanic earthquake swarm model (McNutt, 1996)
Keywords:volcanic seismicity, pre-eruption time, McNutt model
It is known that volcanic seismic activity increases before a volcanic eruption. The generic volcanic earthquake swarm model (McNutt, 1996) (hereinafter referred to as the “McNutt model”) is a classical scenario model that qualitatively explains pre-eruption activities.
In this study, we examined the pre-eruption seismic history in 27 eruptions that have occurred in Japan in recent years, while referring to the McNutt model. As a result, most eruptions occur a while after the peak of seismic activity, with the exception of three cases: the 1977 eruption of Mt. Usu, the 2008 eruption of Mt. Shinmoedake, and the 2018 eruption of Mt. Motoshirane.
The former two eruptions had no peak of seismic activity before the eruption, and the latter had no seismic activity at all before the eruption.
The McNutt model is based on eight magma eruptions. However, in this study, the 24 eruptions other than the three mentioned above also included many phreatic eruptions. The McNutt model can be explained not only by magma but also by high temperature and large amounts of volatile substances.
Furthermore, a high negative correlation was found between the logarithm of eruption volume and the logarithm of the “pre-eruption time”. (Pre-eruption time is defined as the period from the day when the number of earthquakes exceeds the number of earthquakes at the time of the eruption to the day of the eruption in the 90 days before the eruption.) This result indicates that eruptions with larger ejecta tend to have shorter the pre-eruption times. Monitoring seismic activity leading up to an eruption may be able to evaluate the scale of an eruption that will occur afterwards.
In this study, we examined the pre-eruption seismic history in 27 eruptions that have occurred in Japan in recent years, while referring to the McNutt model. As a result, most eruptions occur a while after the peak of seismic activity, with the exception of three cases: the 1977 eruption of Mt. Usu, the 2008 eruption of Mt. Shinmoedake, and the 2018 eruption of Mt. Motoshirane.
The former two eruptions had no peak of seismic activity before the eruption, and the latter had no seismic activity at all before the eruption.
The McNutt model is based on eight magma eruptions. However, in this study, the 24 eruptions other than the three mentioned above also included many phreatic eruptions. The McNutt model can be explained not only by magma but also by high temperature and large amounts of volatile substances.
Furthermore, a high negative correlation was found between the logarithm of eruption volume and the logarithm of the “pre-eruption time”. (Pre-eruption time is defined as the period from the day when the number of earthquakes exceeds the number of earthquakes at the time of the eruption to the day of the eruption in the 90 days before the eruption.) This result indicates that eruptions with larger ejecta tend to have shorter the pre-eruption times. Monitoring seismic activity leading up to an eruption may be able to evaluate the scale of an eruption that will occur afterwards.