Cascadia OBS Noise

Cascadia OBS Noise
Deep Water- Vertical and pressure from J45A 2747m
J45A Z, X, Y, Z −XYP
J45A P
6
10
−8
10
Vertical Acceleration
Pressure DPG
microseisms
noise from shipping, etc.
Infragravity waves
microseisms
4
10
−10
10
horizontals effected by current
2
10
−12
10
Pa2/Hz
m/s2)2/Hz
sms
0
10
−14
10
−2
10
−16
10
Infragravity wave loading
−4
10
−18
10
−3
10
−2
10
−1
10
Hz
0
10
1
10
−3
10
−2
10
−1
10
Hz
0
10
1
10
Run spectra on 4 day long sections of data
from entire data set. (may include some data
during OBS recovery). Some spectra shown
have more d.o.f, and lower resolution by a
factor of 8 than others (shows up in the min
freq. and std dev. of spectra).
Sort and bin spectral data and determine 0, 10,
20%.. 100% spectral values. Dark blue is the
median value. 0 and 100% values (max and min)
are cyan.
Wave Pressure Noise and Wave Loading
Webb and Crawford, BSSA, 2010
APG DATA
1908m
1540m
154m
54m
Pressure Vertical Acceleration from FN07 154m
FN07A P
10
FN07A Z
10
Infragravity waves
8
−8
10
10
−10
10
6
m/s2)2/Hz
10
Pa2/Hz
Infragravity wave loading
4
10
2
−12
10
−14
10
10
0
10
−16
10
−2
10
−18
10
−3
10
−2
10
−1
10
Hz
0
10
1
10
−3
10
−2
10
−1
10
Hz
0
10
1
10
FN07A Coherence
1
The coherence between vertical
acceleration and pressure is very high in
the infragravity wave band, allowing very
accurate calculation of the vertical
deformation from wave loading from the
pressure record and removal from the
vertical component record.
0.998
0.996
0.994
0.992
0.99
0.988
0.986
FN07A Coherence
coherence (expanded scale)
−2
−1
10
1
10
FN07AHz
Compliance
0.9
coherence
0.8
−8
10
0.7
0.6
−9
(m/s2)/Pa
10
0.5
0.4
−10
10
0.3
0.2
0.1
0 −4
10
−11
10
−3
10
−2
10
−1
10
Hz
0
10
1
10
2
10
transfer function between
pressure and vertical
acceleration
−2
−1
10
10
Hz
Vertical Acceleration from J42A 1540m
Vertical original
Vertical after using pressure signal and
compliance function to remove wave
loading noise
Vertical Acceleration from FN07A 154m
Vertical after using pressure signal and
compliance function to remove wave
loading noise
Vertical original
FN07A Z
FN07A Z−XYP
−8
−8
10
10
−10
−10
10
m/s2)2/Hz
m/s2)2/Hz
10
−12
10
−14
−14
10
10
−16
−16
10
10
−18
10
−12
10
−18
−3
10
−2
10
−1
10
Hz
0
10
1
10
10
−3
10
−2
10
−1
10
Hz
0
10
1
10
Removal of infragravity wave
loading signal from vertical
acceleration record. (Webb
and Crawford, BSSA, 1999).
Trawl Shields- Shielding of Horizontals from Current
FN14 173m, trawl
shielded LDEO OBS
J50 1908m, unshielded
standard LDEO OBS
Langseth Airgun from site FN07A, 154m depth
APG
Z
high pass filtered at 1 Hz
Coherence between diff(Z) and diff(pressure)
from short airgun record
Spectra of diff(Z) and diff(P)
from short airgun record
and background spectrum

Download Report