Ultra and Very Long Period Seismic Signatures of Unsteady Eruptions Predicted From Conduit Flow Models

• Explosive volcanic eruptions radiate seismic waves as a consequence of pressure and shear traction changes within the conduit/chamber system. Kinematic source inversions utilize these waves to determine equivalent seismic force and moment tensor sources, but relation to eruptive processes is often ambiguous and nonunique. In this work, we provide an alternative, forward modeling approach to calculate moment tensor and force equivalents of a model of eruptive conduit flow and chamber depressurization. We explain the equivalence of two seismic force descriptions, the first in terms of traction changes on conduit/chamber walls, and the second in terms of changes in magma momentum, weight, and momentum transfer to the atmosphere. Eruption onset is marked by a downward seismic force, associated with loss of restraining shear tractions from fragmentation. This is followed by a much larger upward seismic force from upward drag of ascending magma and reduction of magma weight remaining in the conduit/chamber system. The static force is upward, arising from weight reduction. We calculate synthetic seismograms to examine the expression of eruptive processes at different receiver distances. Filtering these synthetics to the frequency band typically resolved by broadband seismometers produces waveforms similar to very long period seismic events observed in strombolian and vulcanian eruptions. However, filtering heavily distorts waveforms, accentuating processes in early, unsteady parts of eruptions and eliminating information about longer (ultra long period time scale depressurization and weight changes that dominate unfiltered seismograms. Our workflow can be utilized to directly and quantitatively connect eruption models with seismic observations.Plain Language SummaryVolcanic eruptions radiate seismic waves that can be recorded by seismometers placed on and around a volcano. Analysis of seismic data enables one to study eruptions, in particular the processes occurring in the magma-filled conduit and chamber that feeds the eruption. One process of particular interest is fragmentation, in which magma containing a mixture of liquid melt and gas bubbles breaks apart in the conduit and erupts explosively from the vent. We perform computer simulations of explosive eruptions and then use the output of those simulations to predict seismic radiation. We examine the seismograms produced by this workflow to identify features that are diagnostic of process, such as fragmentation, that occur at different times in the eruption. These predictions will guide interpretation of seismic data from real eruptions.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geofysik (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geophysics (hsv//eng)

Nyckelord

volcano seismology

volcanic source representation

unsteady conduit flow modeling

Geophysics with specialization in Seismology

Geofysik med inriktning mot seismologi

Beräkningsvetenskap

Scientific Computing

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