1. 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, Alaska
October 17, 2003

2. Eight sensor array at I55US with Erebus volcano

3. Erebus seismic tremor infrasound 9/17/02
Trace Velocity
0.339 Km/sec
Azimuth
339 deg.
Maximum peak-
To-peak Amp
0.02 Pascal

4. Abs(fft) tremor infrasound 05:05 to 05:05:30, 260
0.86 sec

5. Erebus Tremor Infrasound 9/17/02, 05:05:30-05:06:00 UT
Velocity
0.308 km/sec
Azimuth
341 deg.

6. Abs(fft) tremor infrasound 12:25 to 12:26 UT day 260
0.89 sec

7. abs(fft) Erebus infrasound 13:05 to 13:06, day 260
1.08 sec

8. MCCM detector plot Erebus infrasound Sept 17,2002 12:00 to 13:00 UT
Trace Velocity
340 deg.
Azimuth

9. MCCM detector plot for random noise on all eight sensors at I55US
Sensor Number 1
MCCM value; 0 to 1
Trace Velocity
Azimuth of arrival
One hour of time

10. Phase-aligned overlay inner three sensors of tremor infrasound day 260, 04:01 to 04:10 UT

11. Uncertainty in velocity and azimuth for tremor infrasound day 260, 04:01 to 04:10
Velocity = 307 m/sec +/ m/sec
Azimuth = 340 +/ deg

12. Scatter diagrams for velocity, slowness and wavenumber space for tremor inf. Day 260

13. MCCM Detector plot, I55US, 9/17/02 filtered data (0
MCCM Detector plot, I55US, 9/17/02 filtered data (0.7 to 10 Hz) inner sensors only
MCCM
Velocity
340 deg.
Azimuth

14. Azimuth of Arrival for 24 hours 9/17/02 I53US
340 deg.

15. Trace Velocity I53US 09/17/02
0.350 km/s
0.30 km/s

16. MCCM detector plot, I55US 8/24/02, filtered (0.7 to 10 Hz)
340 deg.

17. MCCM plot I55US 6/03/03 filtered (0.70 to 10 Hz)
340 deg.

18. Tremor signal detector plot day 260 04:00 to 05:00 UT

19. Tremor signal detector plot day 260 05:00 to 06:00 UT

20. 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 +/ deg, with an average trace velocity of /- 3.0 m/sec
The average amplitude of these signals is 0.01 Pa, with a duration up to 5 hours

21. Impulsive Signals from Strombolian-type eruptions from the lava lake in the Erebus Crater
Phase-aligned overlay of 8 sensor traces

22. Erebus Crater with lava lake eruption

23. Strombolian type Erebus signal 8/13/2002
Seconds

24. Statistics of impulsive signals
182 Erebus signals received at I55US
Period April 2002 to March 2003
Average trace vel = / m/sec
Average Azimuth = / 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.