Harmonic Tremor on Active Volcanoes: Seismo-Acoustic Wavefields

Harmonic Tremor on Active Volcanoes: Seismo-Acoustic Wavefields Spectrogram of Karymsky Volcano chugging, 1997. Lines represent the fundamental and possible integer harmonics of the chugging sequence.
Harmonic tremor is often observed on active volcanoes where seismo-acoustic arrays are deployed. In this presentation we review characteristic observational phenomena and discuss the continuum from monochromatic, oscillatory behavior through periodic acoustic pulses (i.e. chugging) to spasmodic drumming on numerous volcanoes world wide. Harmonic tremor can provide detailed constraints on physical parameters controlling activity in active vents through physical modeling. These include physical constraints on the vent geometry, composition and density of the multiphase fluids, and visco-elastic parameters of choked flow in the conduits. Examples will show seismic tremor with and without an associated acoustic emission, an indicator of dynamic processes occurring at the top of the active vent. While explosive activity can range widely between volcanoes, harmonic tremor often exhibits remarkably similar behavior on vents as diverse as Karymsky, Tungurahua, Reventador, and Santiaguito Volcanoes. For example, chugging activity typically has a consistent 0.7-2 Hz signal on many volcanoes world wide. Commonly observed gliding, where frequency modulates over time, suggests that conditions in the conduit are non-stationary, and must be treated with specialized time series analysis tools. We explore these phenomena and highlight possible models explaining these near surface vent emissions.
</p><p>Lees, J.M., Johnson, J.B., Ruiz, M., Troncoso, L. and Welsh, M., (2008). Reventador Volcano 2005: Eruptive Activity Inferred from Seismo- Acoustic Observation. J. Volcanol. Geotherm. Res., 176(1): 179-190, doi:10.1016/j.jvolgeores.2007.10.006.
</p><p>Lees, J.M. and Ruiz, M., (2008). Non-linear Explosion Tremor at Sangay, Volcano, Ecuador. J. Volcanol. Geotherm. Res., 176(1): 170-178 doi:10.1016/j.jvolgeores.2007.08.012
</p><p>Johnson, J. B., and J. M. Lees (2000), Plugs and Chugs – Strombolian activity at Karymsky, Russia, and Sangay, Ecuador, J. Volcanol. Geotherm. Res., 101, 67-82.
</p><p>Acknowledgements: NSF: EAR-9614639 , "Side Edge of Kamchatka Slab", June 1, 1997-July 31, 2000. NSF Proposal No: EAR-0738768 Title: Co</p>


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