Abstract
Volcano seismicity is one of the key parameters to understand magma dynamics of erupting volcanoes. However, the physical process at the origin of the resulting complex and broadband seismic signals remains unclear. Syn-eruptive very long period (VLP) seismic signals have been explained in terms of the sudden expansion of gas pockets rising in the liquid melt. Their origin is linked to a magma dynamics which triggers the explosive process occurring before the explosive onset. We provide evidence based on acoustic, thermal, and ground deformation data to demonstrate that VLP signals at Stromboli are generated at the top of the magma column mainly after the explosion onset. We show that VLP amplitude and duration scale with the eruptive flux which induces a decompression of 103–104 Pa involving the uppermost ~ 250 m of the feeding conduit. The seismic VLP source represents the final stage of a ~ 200 s long charge and discharge mechanism the magma column has to release excess gas accumulated at the base of a denser and degassed magma mush. The position of the VLP seismic source coincides with the centroid of the shallow mush plug and tracks elevation changes of the magma free surface.
Highlights
Volcano seismicity is one of the key parameters to understand magma dynamics of erupting volcanoes
In this paper we present evidence incorporating thermal imagery, acoustic pressure, and ground deformation data to produce a new physical model that explains the seismic very long period (VLP) as the final stage of recurrent charge/ discharge of the excess gas accumulated in the shallow part of the feeding conduit, connecting the VLP source to the surface of the magma column and to the eruptive flux
Quasi-static displacement modelling of vertical ground motion[54,57], using an unprecedented seismic network deployment in very near field conditions, indicates that the source of seismic VLP is located within the crater area and it has an extension of ~ 250 m below the craters
Summary
Volcano seismicity is one of the key parameters to understand magma dynamics of erupting volcanoes. Syn-eruptive very long period (VLP) seismic signals have been explained in terms of the sudden expansion of gas pockets rising in the liquid melt. Their origin is linked to a magma dynamics which triggers the explosive process occurring before the explosive onset. This interpretation has contributed to picturing the geometry of the shallow feeding system at Stromboli and to explaining the VLP source process as a pressure source within an opening/
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