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| Title: | Analysis of Seismic Similarity in Strombolian Eruptions from Mount Erebus, Antarctica |
| Authors: | Henderson, David Brent |
| Keywords: | Interferometry
Seismic waves
Seismic prospecting |
| Issue Date: | 1-Dec-2008 |
| Abstract: | Mount Erebus has long been recognized to produce very similar seismic
signatures associated with its Strombolian eruptions. Preliminary research performed on
similar seismograms from December 1999 to January 2000 suggested a sudden
decorrelation of the coda, accompanied by relative stability in the early seismogram.
Using coda wave interferometry, this decorrelation was interpreted as a median change
within the volcano. Closer examination of this data in this thesis shows that clipping due
to event size variations as well as more subtle features controlled by event size strongly
influence such analysis techniques.
Once it became obvious that source effects were very important influences on
seismogram similarity, more sophisticated methods were implemented to better
understand them. A moving window cross correlation analysis demonstrated more
comprehensively that eruption size is a significant factor in seismogram similarity. A
surprising discovery to come out of this research was the existence of time bands of
strong correlation, probably arising from scatterers within the volcano at some distance
(km) from the lava lake, which are even visible in the late coda (30+ s). Invariance is
seen in the corresponding correlation lags associated with these scatterers, indicating
stability in medium velocity.
Clustering the whole waveform seismograms also showed that size is the primary
determiner of seismogram similarity. However, the fact that several clusters can have the
same size (and even be active simultaneously) showed that other variable source
processes must be involved as well. Videos of eruptions, as well as infrasound data,
showed that other possible source process variations that may be important in this context
include location of the bubble in the lava lake, lava lake convection phenomena (i.e., the
lava lake state during eruption), and the geometry or pressure of the eruptive gas slug.
Overall, similarities in how the initial and coda parts of the seismogram cluster also
indicate that seismogram variability is due to source processes.
Clustering the infrasound data resulted in completely different clusters then the
seismic data. The clusters for the infrasound data were very similar, except for the rate of
change of the first motion. This indicates that infrasound clusters are especially sensitive
to rupture processes, making them promising for measuring lava lake rupture process. |
| URI: | http://hdl.handle.net/10136/183 |
| Appears in Collections: | Theses
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| Henderson, David Brent.pdf | | 4172Kb | Adobe PDF | View/Open |
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