Geophysics
Chaotic Tremor

Chaotic Tremor

Vertical component seismograms and spectrograms from January 2, 2003 recorded at broadband station E1S (0.7 km from the lava lake) and short-period station MAC (2.07 km from the lava lake). Time units are shown in seconds. This tremor episode exhibits a broad spectrum. The spatial distribution of amplitudes suggests a shallow source close to the crater. Twenty minutes after the tremor onset, a brief (approximately 2 minutes) transition to harmonic trigger-type tremor with three harmonics and a fundamental frequency of 3.0 Hz can be seen. This audio record is sped up by a factor of 100 relative to the actual seismic signal.

 
Iceberg Tremor

Tremor Sonogram
The audio file above is a time compressed harmonic tremor from Mt. Erebus. The signal representation above, called a "sonogram" or "spectrogram", shows the evolving spectral content of the audo signal as a function of time. The tremor was recorded on February 3, 2001. The audio is a vertical seismogram, with a sampling rate of 40 samples per second, sped up 100 times to transpose the very slow seismic frequencies into the audible frequency band. Thus, the true data length is 1 hour but ths sound file is compressed to less than 1 minute. The sound file is rather trombone-like in character.

 
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