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.