Observations of volcanic tremor during the January

Authors: Silvio De Angelis Stephen R McNutt

Publish Date: 2007/03/06

Volume: 69, Issue: 8, Pages: 927-940

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Abstract

Mt Veniaminof Alaska Peninsula is a stratovolcano with a summit icefilled caldera containing a small intracaldera cone and active vent From January 2 to February 21 2005 Mt Veniaminof erupted The eruption was characterized by numerous small ash emissions VEI 0 to 1 and accompanied by lowfrequency earthquake activity and volcanic tremor We have performed spectral analyses of the seismic signals in order to characterize them and to constrain their source Continuous tremor has durations of minutes to hours with dominant energy in the band 05–40 Hz and spectra characterized by narrow peaks either irregularly nonharmonic tremor or regularly spaced harmonic tremor The spectra of nonharmonic tremor resemble those of lowfrequency events recorded simultaneously with surface ash explosions suggesting that the source mechanisms might be similar or related We propose that nonharmonic tremor at Mt Veniaminof results from the coalescence of gas bubbles while lowfrequency events are related to the disruption of large gas pockets within the conduit Harmonic tremor characterized by regular and quasisinusoidal waveforms has duration of hours Spectra containing up to five harmonics suggest the presence of a resonating source volume that vibrates in a longitudinal acoustic mode An interesting feature of harmonic tremor is that frequency is observed to change over time spectral lines move towards higher or lower values while the harmonic nature of the spectra is maintained Factors controlling the variable characteristics of harmonic tremor include changes in acoustic velocity at the source and variations of the effective size of the resonatorThe authors are grateful to the staff of the Alaska Volcano Observatory for their efforts during the course of the eruption We thank two anonymous reviewers for their insightful comments and J Stix for a final review of the manuscript This work was supported by the Alaska Volcano Observatory and the US Geological Survey as part of the Volcano Hazards Program and by additional funds from the State of Alaska

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