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
Eight sensor array at I55US with Erebus volcano
Erebus seismic tremor infrasound 9/17/02
Trace Velocity 0.339 Km/sec
Azimuth 339 deg.
Maximum peak-To-peak Amp0.02 Pascal
Abs(fft) tremor infrasound 05:05 to 05:05:30, 260
0.86 sec
Erebus Tremor Infrasound 9/17/02,05:05:30-05:06:00 UT
Velocity 0.308 km/sec
Azimuth341 deg.
Abs(fft) tremor infrasound 12:25 to 12:26 UT day 260
0.89 sec
abs(fft) Erebus infrasound 13:05 to 13:06, day 260
1.08 sec
MCCM detector plot Erebus infrasound Sept 17,2002 12:00 to 13:00 UT
MCCM
Trace Velocity
Azimuth340 deg.
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
Phase-aligned overlay inner three sensors of tremor infrasound day 260, 04:01 to 04:10 UT
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
Scatter diagrams for velocity, slowness and wavenumber space for tremor inf. Day 260
MCCM Detector plot, I55US, 9/17/02 filtered data (0.7 to 10 Hz) inner sensors only
MCCM
Velocity
Azimuth
340 deg.
Azimuth of Arrival for 24 hours 9/17/02 I53US
340 deg.
Trace Velocity I53US 09/17/02
0.350 km/s0.30 km/s
MCCM detector plot, I55US 8/24/02, filtered (0.7 to 10 Hz)
340 deg.
MCCM plot I55US 6/03/03 filtered (0.70 to 10 Hz)
340 deg.
Tremor signal detector plot day 260 04:00 to 05:00 UT
Tremor signal detector plot day 260 05:00 to 06:00 UT
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
Impulsive Signals from Strombolian-type eruptions from
the lava lake in the Erebus Crater
Phase-aligned overlay of 8 sensor traces
Erebus Crater with lava lake eruption
Strombolian type Erebus signal 8/13/2002
Seconds
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.