Erebus Putative Seismic-Tremor Infrasound observed at I55US on day 260, 2002, Sep.17
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Erebus Putative Seismic-Tremor Infrasound observed at I55US on
day 260, 2002, Sep.17
Charles R. Wilson, John V. Olson and Daniel L. Osborne, Geophysical Institute, University
of Alaska at Fairbanks, AlaskaOctober 17, 2003
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Eight sensor array at I55US with Erebus volcano
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Erebus seismic tremor infrasound 9/17/02
Trace Velocity 0.339 Km/sec
Azimuth 339 deg.
Maximum peak-To-peak Amp0.02 Pascal
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Abs(fft) tremor infrasound 05:05 to 05:05:30, 260
0.86 sec
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Erebus Tremor Infrasound 9/17/02,05:05:30-05:06:00 UT
Velocity 0.308 km/sec
Azimuth341 deg.
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Abs(fft) tremor infrasound 12:25 to 12:26 UT day 260
0.89 sec
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abs(fft) Erebus infrasound 13:05 to 13:06, day 260
1.08 sec
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MCCM detector plot Erebus infrasound Sept 17,2002 12:00 to 13:00 UT
MCCM
Trace Velocity
Azimuth340 deg.
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MCCM detector plot for random noise on all eight sensors at I55US
Random Noise Sensor Number 1
MCCM value; 0 to 1
Trace Velocity
Azimuth of arrival
One hour of time
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Phase-aligned overlay inner three sensors of tremor infrasound day 260, 04:01 to 04:10 UT
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Uncertainty in velocity and azimuth fortremor infrasound day 260, 04:01 to 04:10
Velocity = 307 m/sec +/- 1.35 m/sec
Azimuth = 340 +/- 0.25 deg
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Scatter diagrams for velocity, slowness and wavenumber space for tremor inf. Day 260
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MCCM Detector plot, I55US, 9/17/02 filtered data (0.7 to 10 Hz) inner sensors only
MCCM
Velocity
Azimuth
340 deg.
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Azimuth of Arrival for 24 hours 9/17/02 I53US
340 deg.
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Trace Velocity I53US 09/17/02
0.350 km/s0.30 km/s
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MCCM detector plot, I55US 8/24/02, filtered (0.7 to 10 Hz)
340 deg.
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MCCM plot I55US 6/03/03 filtered (0.70 to 10 Hz)
340 deg.
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Tremor signal detector plot day 260 04:00 to 05:00 UT
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Tremor signal detector plot day 260 05:00 to 06:00 UT
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Continuous-Type Erebus “tremor” signals
• During the year 2002 four episodes have been found in the I55US data set of very low amplitude, continuous-type infrasound from an average azimuth of 340 +/- 0.78 deg, with an average trace velocity of 329.50 +/- 3.0 m/sec
• The average amplitude of these signals is 0.01 Pa, with a duration up to 5 hours
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Impulsive Signals from Strombolian-type eruptions from
the lava lake in the Erebus Crater
Phase-aligned overlay of 8 sensor traces
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Erebus Crater with lava lake eruption
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Strombolian type Erebus signal 8/13/2002
Seconds
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Statistics of impulsive signals
• 182 Erebus signals received at I55US• Period April 2002 to March 2003 • Average trace vel = 320.5 +/- 6.32 m/sec• Average Azimuth = 336.5 +/- 0.39 deg• The impulsive signals were filtered in the
passband 0.70 to 10 Hz to eliminate the microbarom background
• Impulsive signals are coherent over the entire 8 sensor array of aperture 1.9 km.