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| Titel |
A comparison of active seismic source data to seismic excitations from the 2012 Tongariro volcanic eruptions, New Zealand |
| VerfasserIn |
Arthur Jolly, Ben Kennedy, Harry Keys, Ivan Lokmer, Jon Proctor, John Lyons, Gillian Jolly |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089004
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| Publikation (Nr.) |
 EGU/EGU2014-3185.pdf |
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| Zusammenfassung |
| The 6 August 2012 eruption from Tongariro volcano’s Te Maari vent comprised a complex
sequence of events including at least 4 eruption jets, a large chasm collapse, and a debris
avalanche (volume of ~7x105 m3) that propagated ~2 km beyond the eruptive vent. The
eruption was poorly observed, being obscured by night time darkness, and the eruption
chronology must be unravelled instead from a complex seismic record that includes discrete
volcanic earthquakes, a sequence of low to moderate level spasmodic tremor and an intense
burst of seismic and infrasound activity starting at 11:52:18 UTC that marked the eruption
onset. We have discriminated the timing of the complex surface activity by comparing active
seismic source data to the eruptive sequence. We dropped 11 high impact masses from
helicopter to generate a range of active seismic sources in the vicinity of the eruption
vent, chasm, and debris avalanche areas. We obtained 8 successful drops having
an impact energy ranging from 3 to 9x106 joules producing seismic signals to a
distance of 5 to 10 km and having good signal to noise characteristics in the 3-12 Hz
range. For the 8 drops, we picked first-P arrival times and calculated amplitude
spectra for a uniform set of four 3-component stations. From these, we obtained a
distribution of amplitudes across the network for each drop position which varied
systematically from the eruption vent and avalanche scar to the debris avalanche
toe. We then compared these proxy source excitations to the natural eruption and
pre-eruption data using a moving window cross-correlation approach. From the correlation
processing, we found evidence for the debris avalanche a few minutes prior to the
eruption in both the broad spectrum and narrow frequency (5-10 Hz) analysis. The
total seismic energy release calculated from the new method is ~8x1011 joules,
similar to an independently estimated calculation based on the radiated seismic
energy. The inferred seismic energy release for the debris avalanche (~109 Nm) is
several orders of magnitude smaller than the available potential energy, a result
that suggests that these surface excitations are inefficiently coupled into seismic
waves. We conclude that active source seismic mass drops are suitable proxies for
seismic surface processes, offering an easy and effective method to estimate the
location and energy release for a wide range of energetic surface mass movements. |
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