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.
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Publication:
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Geophysical Research Letters
Pub Date:
- April 2006 DOI:
- Bibcode:
- 2006GeoRL..33.7306D Keywords:
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- Seismology: Volcano seismology (8419);
- Volcanology: Volcano monitoring (7280);
- Volcanology: Hydrothermal systems (0450;
- 1034;
- 3017;
- 3616;
- 4832;
- 8135)