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Analyses of unusual long-period earthquakes with extended coda recorded at Katmai National Park, Alaska, USA

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Abstract

A swarm of six long-period (LP) events with slowly decaying coda wave amplitudes and durations up to 120 s, was recorded by seismic stations located in the proximity of Mt. Griggs, a fumarolically active volcano in the Katmai National Park, Alaska, during December 8-21, 2004. Spectral analyses reveal the quasi-monochromatic character of the waveforms, dominated by a 2.5 Hz mode frequently accompanied by a weaker high-frequency onset (6.0-9.0 Hz). Particle motion azimuths and inclination angles show a dominant WNW-ESE direction of polarization for all the signals, and suggest that seismic energy is radiated by a stable source at shallow depth. Damping coefficients between 0.0014 and 0.0063 are estimated by fitting an exponential decay model to the signal's coda; corresponding quality factors range from 78 to 351. The source of the waveforms is modelled as a resonant cavity filled with a fluid/gas mixture.


Publication:

Geophysical Research Letters

Pub Date:
April 2006
DOI:

10.1029/2005GL025581

Bibcode:
2006GeoRL..33.7306D
Keywords:
  • Seismology: Volcano seismology (8419);
  • Volcanology: Volcano monitoring (7280);
  • Volcanology: Hydrothermal systems (0450;
  • 1034;
  • 3017;
  • 3616;
  • 4832;
  • 8135)