Recent Developments in Analyzing Infrasonic Signals Observed at I55US

1
Recent Developments in Analyzing Infrasonic
Signals Observed at I55US

• Kenneth M. Arnoult, John V. Olson,
• Charles R. Wilson, C. A. L. Szuberla,
• and D. Osborne
• Infrasound Group, University of Alaska Fairbanks

Presented at the Infrasound Technology
Workshop Scripps Research Institute, UC San Diego
2
I55US Windless Bight, Antarctica
I55US, the CTBT infrasound site, is located on
the Ross ice shelf approximately 30 km from
McMurdo base.
3
CTBT Array Geometry
The UAF CTBT installations are constructed using
8 sensors in the form of a pentagram surrounding
a triangle. This provides broad-band coverage of
the k-spectrum. Data are taken at 20 Hz.
4
Previously Explained Signals

• Strombolian Signals from Erebus
• Signals from Vee Cliffs
• Mountain Associated Waves (MAWs) from New Zealand
• Microbaroms

5
Strombolian signal from Erebus
Mt. Erebus, located approximately 25 km from the
infrasound site, is an active volcano producing
occasional small strombolian eruptions.
6
Strombolian signal from Erebus

• Statistics for 1 year
• 182 signals observed
• ( 1 signal every 2 days)
• Trace Velocity
• 320.5 /- 6.32 m/s
• Azimuth
• 336.5 /- 0.39o
• Duration
• 5 s

Sensors
Overlay
7
Vee Cliffs Ice Avalanche

• Common Characteristics
• Trace velocity
• 327.4 /- 1.5 m/s
• Azimuth
• 19.0 /- 2.0o
• Duration
• 10s 30s

Sensors
Overlay
8
Mountain Associated Wavesfrom New Zealand

• Common Characteristics
• Frequency
• 0.015 0.100 Hz
• Duration
• Hours to Days
• Low correlation
• Seasonal Variation

Sensors
Overlay
9
Microbaroms

• Common Characteristics
• Frequency
• 0.2 Hz
• Low Spatial Correlation
• Seasonal Variation

Inner 3 Sensors
Overlay
10
Recently Explained Signals

• Signals from Erebus Tremors
• Signals from Ice Shelf/Island Interface

11
Signal from Erebus Tremors

• 4 Signals Observed
• Trace Velocity
• 329.5 /- 3.0 m/s
• Azimuth
• 340.0 /- 0.78o
• Average Amplitude
• 0.01 Pa

Inner 3 Sensors
Overlay
12
Ice Shelf Signal

• Common Characteristics
• Azimuth
• - Highly Variable
• - Usually Northern
• Duration
• 5s 30s
• Highly Variable Waveforms
• High Correlation

Sensors
Overlay
13
Locator function

• Assumptions
• Spherical wave propagation
• (Temperature is constant and uniform)
• No wind
• Earth is flat
• Precise Tau Precise Location
• Sampling Delta Tau Ovals

14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
Summary

• Erebus Study
• Recently Explained Signals
• Signals from Erebus Tremors
• Signals from Ice Shelf/Island Interface
• Near Field Source Locator