Helicopter vs. volcanic tremor: Characteristic features of seismic harmonic tremor on volcanoes

Eibl, Eva P. S. and Lokmer, Ivan and Bean, Christopher J. and Akerlie, Eggert and Vogfjörd, Kristin S. (2015) Helicopter vs. volcanic tremor: Characteristic features of seismic harmonic tremor on volcanoes. Journal of Volcanology and Geothermal Research, 304. pp. 108-117.

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Abstract

We recorded high-frequency (> 10 Hz) harmonic tremor with spectral gliding at Hekla volcano in Iceland. Particle motion plots indicated a shallow tremor source. We observed up to two overtones beneath our Nyquist frequency of 50 Hz and could resolve a source of closely spaced pulses of very short duration (0.03 - 0.1 s) on zoomed seismograms. Volcanic tremor with fundamental frequencies above 5 Hz, frequency gliding and/or repetitive sources similar to our observations were observed on different volcanoes around the world. However, this frequency content, duration and occurrence of volcano-related tremor was not observed in the last 35 years of seismic observations at Hekla. Detailed analysis reveals that this tremor was related to helicopters passing the volcano. This study relates the GPS track of a helicopter with seismic recordings of the helicopter at various distances. We show the effect the distance, number of rotor blades and velocity of the helicopter has on the observed up and down glidings at up to 40 km distance. We highlight similarities and differences between volcano-related and helicopter tremor in order to help avoid misinterpretations.

Item Type: Article
Uncontrolled Keywords: Frequency gliding, Doppler shift, Harmonic tremor, Helicopter, Volcano,
Divisions: School of Cosmics Physics
School of Cosmics Physics > Geophysics
Date Deposited: 05 Apr 2018 12:52
Last Modified: 05 Apr 2018 12:52
URI: http://dair.dias.ie/id/eprint/381

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