1. Ambient Seismic Noise Correlation on Iceberg C16, Ross Sea, Antarctica
C53A-0286
YitanWang†
, Doug MacAyeal†
and Emile Okal††
†
Physical Sciences Division, University of Chicago; ††
Department of Earth and Planetary Sciences, Northwestern University
yitanwangnju@uchicago.edu, drm7@uchicago.edu, emile@earth.northwestern.edu
A. The Questions:
B. Field Location: Ross Sea, Antarctica.
C. Method and Results: D. Possible Interpretation:
E. Conclusions:
- 4 seismometers
on iceberg C16.
(A, B, C & D)
- 60-day deploy-
ment
- noise source:
collision zone be-
tween B15A and
C16.
- C16 is aground
- ~800 m deep
water, ~75 m ice
thickness
−1
−0.5
0
0.5
1 x 10
4 C16A: HHZ
Record section of correlation functions:
Noise correlation function:
Correlation function plots (stations B and A):
• Can ambient-noise tomography assess
structure and changing conditions of float-
ing ice shelves (and icebergs)?
• Can cross-correlation of diverse, diffuse
seismic noise signals on an iceberg between
stations help to identify seismic propagation
modes?
example of diffuse “iceberg tremor”
−500 −400 −300 −200 −100 0 100 200 300 400 500
−3
−2
−1
0
1
2
3
seconds
07−Jan−2004 02:00 - 04:00 | HHZ channels | Low Pass: < 0.1 Hz
−15 −10 −5 0 5 10 15
−10
−8
−6
−4
−2
0
2
4
6
8
10
seconds
07−Jan−2004 02:00 - 04:00 | HHZ channels | High Pass: > 10 Hz
low-pass filter:
high-pass filter:
time lag (s)
time lag (s)
7.5 s lag
fast phase
(hydroacoustic)
scaledamplitude
scaledamplitude
~100 s lag
slow phase
(flexural-gravity wave)
D−A
Bandpass filter | 2 to 6 Hz
−10
0
5
10
15
20
25
30
35
40
45
50
station−sourcedistancedifference(km)
0 10 20 30 40 50
time lag (s)
A−B
C−A
D−A
C−B
D−B
D−C
3000 m/s 1460 m/s
station pairs
screech!!
seismic waves in ice
iceberg collision
noise source
sea bed
hydroacoustic wave
(T phase)
surface flexure/gravity waves
ocean water
ice
ice
χij
(Δt) = di
(t+Δt)⋅dj
(t) dt1__
σ ⌡
⌠
di
(t) = seismic signal, station i , Δt = time lag
• Ambient noise on C16 is consistent with
specific source in iceberg collision zone that
radiates almost continuously.
• Record sections reveal multiple phases of
propagation consistent with: (a) “fast” seismic
phases in ice (or below seabed), (b) hydro-
acoustic (T-phase) waves in water layer, and (c)
“slow” flexural gravity waves.
• Potential for characterizing iceberg (or, more
valuably) ice-shelf structure from ambient
noise correlation appears possible.
• Work for future: detect and explain secular
changes in noise correlation functions (e.g.,
changing sources, source location, changing ice
thickness, etc.)
seismic
station
refracted P-phase (head wave)
collision
zone
B
C
A
D
40km
18
km
iceberg C16
B15A
B15J
Ross Island
Ross Sea
distance on vertical axis: Δ source-to-station (km)
0 6 12 15time (m)
counts
unfiltered signal
tremor
field site