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J. V. Olson, K. Arnoult, C. A. L. Szuberla, C. Wilson

IMS Infrasound Station Observations of the Recent Explosive Eruptions of Okmok and Kasatochi Volcanoes, Alaska. J. V. Olson, K. Arnoult, C. A. L. Szuberla, C. Wilson Wilson Infrasound Observatory, Geophysical Institute, University of Alaska Fairbanks, M. Garces ISLA, University of Hawaii,

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J. V. Olson, K. Arnoult, C. A. L. Szuberla, C. Wilson

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  1. IMS Infrasound Station Observationsof the Recent Explosive Eruptions of Okmok and Kasatochi Volcanoes, Alaska J. V. Olson, K. Arnoult, C. A. L. Szuberla, C. Wilson Wilson Infrasound Observatory, Geophysical Institute, University of Alaska Fairbanks, M. Garces ISLA, University of Hawaii, M. Hedlin, L2A, IGPP, University of California, San Diego S. McNutt Alaska Volcano Observatory, Geophysical Institute, University of Alaska Fairbanks Presented at the 2008 International Technical Workshop, Bermuda

  2. The Pacific Basin • Kasatochi volcano • 52.169N, 175.51W • Eruption times: • five major explosive eruptions • beginning ~22:00 UT, 7 Aug • ending ~04:35 UT, 8 Aug • ash emissions became continuous after these events reaching altitudes > 35,000 ft asl I53US Kasatochi Okmok I56US I57US • Okmok volcano • 53.397N, 168.166W • Eruption time: • Explosion: 12 July 08, 19:43 UT with continuing ash emissions • ash cloud top 30-35,000 ft asl I59US ITW Workshop, Bermuda 2008

  3. Eruption Details atat www.avo.alaska.edu Expl’n Date Start Duration # (UTH) (min) 1 7 Aug 22:01 69 2 8 Aug 01:50 27 3 8 Aug 04:35 35 4 8 Aug 07:12 46 5 8 Aug 12:06 26 Kasatochi • Great circle distances to US IMS stations • Kasatochi Expected Travel Time • @ 0.3km/sec • I53US: 2104km @ 241o ~1.95 hrs • I56US: 4060km @ 299o ~3.76 hrs • I57US: 5067km @ 313o ~4.69 hrs • I59US: 4002km @ 340o ~3.71 hrs Kasatochi, 17:00 UT, 8 Aug 08 Photo by JT Ford ITW Workshop, Bermuda 2008

  4. IMS Sites Near the Pole Seventeen IMS infrasound sites are located within about 10,000 km of the volcanic events. The sites labeled with green stars are either under construction or the data was not available to us at this time. The sites labeled with blue stars, I10, I18, I30, I53, I56, I57, I59 will be the subject of this review. I37 I31 I51 I18 I46 I34 I10 I53 I15 I56 I45 I57 I44 K O I30 I58 I60 I59 ITW Workshop, Bermuda 2008

  5. Kasatochi – IMS Arrays(within ~6000 km) I18 I10 I53 I56 I57 K I30 I59 ITW Workshop, Bermuda 2008

  6. Kasatochi Waveforms & SpectraI53US Infrasound amplitudes for the Kasatochi eruptions reached ~ 1 Pa at I53US and I56US ITW Workshop, Bermuda 2008

  7. Signal Detection • Infrasound array data, signal detection • Compute MCCM on sliding window • Lease-Squares azimuth/velocity estimation • Pure-State filter (www.inframatics.org, Sept 04) • Re-compute least-squares azimuth/velocity Pure-State filtering increases the signal-to-noise level and enables detection over longer periods of time Detection: Pure-State filtered data Detection: Raw Data ITW Workshop, Bermuda 2008

  8. Kasatochi: I53 DetectionsPure-State Data I53 Azimuth: 244o Trace velocity: 358 m/sec The MCCM detector along with the least-squares estimates of azimuth, velocity and the residuals (στ) are computed using a sliding window 500 sec long, updated every 50 sec ITW Workshop, Bermuda 2008

  9. Kasatochi: Detections (1)Pure-State Data I18 Azimuth: 299.9o Trace velocity: m/sec I10 Azimuth: 304.8o Trace velocity: m/sec ITW Workshop, Bermuda 2008

  10. Kasatochi: Detections (2)Pure-State Data I56 Azimuth: 300o Trace velocity: 374 m/sec I53 Azimuth: 244o Trace velocity: 358 m/sec ITW Workshop, Bermuda 2008

  11. Kasatochi: Detections (3)Pure-State Data I59 Azimuth: 336o Trace velocity: 312 m/sec I57 No signal found ITW Workshop, Bermuda 2008

  12. Kasatochi: Detections (4)Pure-State Data I30 Azimuth: 47.8o Trace velocity: 370 m/sec ITW Workshop, Bermuda 2008

  13. Kasatochi Simple Back Azimuth Location I18 I53 K I10 I56 K I30 I59 Simple back-azimuth projections along the great-circle between IMS stations results in an average location that is approximately 200 km Southwest of Kasatochi and encompasses a region several hundred km wide. ITW Workshop, Bermuda 2008

  14. Okmok – IMS Arrays(within ~6000 km) I18 I34 I10 I53 I56 I57 O I30 I59 ITW Workshop, Bermuda 2008

  15. Okmok Waveforms (1)I53, I56 ITW Workshop, Bermuda 2008

  16. Okmok Waveforms (2)I57, I59 ITW Workshop, Bermuda 2008

  17. Okmok: Detections (1)Pure-State Data No signal found I53 Azimuth: 236o Trace velocity: 360 m/sec ITW Workshop, Bermuda 2008

  18. Okmok: Detections (2)Pure-State Data No signal found ITW Workshop, Bermuda 2008

  19. Summary • Both eruptions were strong, exposive eruptions lasting several hours and producing extensive ash plumes • Kasatochi: • Amplitudes ~1Pa observed at distances to 4000 km • Simple great-circle back-azimuths give a location ~200 km Southwest of the source • Okmok: • Observed only at I53US, amplitudes ~0.01 – 0.1 Pa • We are collecting atmospheric data: • Effects of wind • Estimate signal paths through time delays ITW Workshop, Bermuda 2008

  20. END ITW Workshop, Bermuda 2008

  21. Eruption Details atat www.avo.alaska.edu Okmok Okmok, 20:00 UT, 3 Aug 08 Photo by Mees, Burke ITW Workshop, Bermuda 2008

  22. Kasatochi Waveforms (2)I57, I59 ITW Workshop, Bermuda 2008

  23. Kasatochi Waveforms (2)I10, I30 ITW Workshop, Bermuda 2008

  24. Kasatochi Spectra ITW Workshop, Bermuda 2008

  25. Kasatochi Spectra ITW Workshop, Bermuda 2008

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