Infrasonic array observations at I53US of the 2006 Augustine Volcano eruptions
The recent January 2006 Augustine eruptions, from the 11th to the 28th, have produced a series of 12 infrasonic signals that were observed at the I53US array at UAF. the eruption times for the signals were provided by the Alaska Volcanic Observatory at UAF using seismic sensors and a Chaparral microphone that are installed on Augustine Island. The bearing and distance of Augustine from I53US are, respectively, 207.8 degrees and 675 km. The analysis of the signals is done with a least-squares detector/estimator that calculates, from the 28 different sensor-pairs in the array, the mean of the cross-correlation maxima (MCCM), the horizontal trace-velocity and the azimuth of arrival of the signal using a sliding-window of 2000 data points. The data were bandpass filtered from 0.03 to 0.10 Hz. The data are digitized at a rate of 20 Hz. The average values of the signal parameters for all 12 Augustine signals are as follows: MCCM=0.85 (std 0.14), Trace-velocity=0.346 (std 0.016) km/sec, Azimuth=209 (std 2) deg. The celerity for each signal was calculated using the range 675 km and the individual travel times to I53US. The average celerity for all ten eruption signals was 0.27 (std 0.02) km/sec. Ray tracing studies, using mean values of the wind speed and temperature profiles (along the path) from NRL, have shown that there was propagation to I53US by both stratospheric and thermospheric ray paths from the volcano.