ultra-high resolution imaging of submarine landslides: the
TRANSCRIPT
ms
- 2-w
ay
Ultra-high Resolution Imaging of Submarine Landslides: the Geoforce Boomer/Sparker Sub-bottom profiler
David C. Mosher, Geological Survey of Canada- Atlantic
Graham Standen Geoforce Group Ltd.
D. Calvin Campbell Geological Survey of Canada- Atlantic
Irena Schulten Dalhousie University
An ideal subbottom profiler has a broad frequency band, high energy, rapid trigger rate, and highly repeatable
Depending on operational water depths and survey demands, either mode can be chosen “on the fly”.
Boomer Source
Boomer Below is a Geofroce DTS profile from
source characteristics. These elements provide for maximum vertical and horizontal resolving capacity, subbottom penetration even in hard and gas-bearing sediments, shot-to-shot coherency and phase and amplitude information to facilitate interpretation. In addition, directional source characteristics limit incidental environmental noise. The Geoforce DTS optimizes these characteristics to the physical limits of modern technologies, utilizing two modes of operation: sparker and boomer.
On the far left is a picture of the housing of the boomer plates that fits within the towed fish. Rapid expansion of the boomer plates accelerates a
Deep tow of the system removes surface and vessel motion (heave, pitch and roll), eliminates the surface ghost, and stabilizes source characteristics. Digitization of received signals within the tow body eliminates cable and EM noise interference. The result is an ideal tool for resolving complex structures such as are present in mass transport deposits.
0.5
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3 1 1.5 2 2.5 3 3.5
Time (ms) 4
2
-2
3
2.5
2
1.5
1
0.5
0
15
10
5
0 5 10 15 20 Freq (kHz)
350
400
350
400
260
280
300
20 km 320
Sparker
260
280
300
Emerald Basin on the Scotian Shelf. The data were filtered and migrated and displayed here in full phase. The profile shows a variety of glacigenic geologic features including till, stacked ice- margin wedges and subbottom ice- rafted debris. Dipping beds of Tertiary bedrock can be seen below the glacial section. Two subbottom profiles of approximately the same ground from this profile are shown to the left; the top panel shows boomer data acquired with an internal, single element hydrophone and displayed as full phase. The
cylindrical plug of water mass that creates a highly directional and highly repeatable pressure wave. On the immediate left is the sparker tail protruding from
-4 15 20 25 30
Time (ms)
0
0 1 2 3 4 5 Freq (kHz)
20 km
320 bottom panel shows data collected in sparker mode and received on an external hydrophone streamer (a 12-
Boomer Plates Sparker Tip
Sambro Moraine
the rear of the tow body. In this case, discharge of energy through the wire tips within a conducting fluid (salt water) creates a spark that vapourizes a surrounding water mass. The vapour bubble collapses rapidy under ambient water pressure, creating an implosion as the impulsive sound source. Variations in ambient pressure (i.e. tow depths) can create different source wavelets, as shown in the figure to the above.
Sparker Source element array towed behind the tow- fish).
300
350
Till
Ice grounding line wedges
LaHave Clay Emerald Silt A
Emerald Silt B
100 km Pockmarks 200
250
400
450
Boulder fields (IRD) Till
Tertiary Bedrock
300
350
Flemish Pass, off of the Grand Banks of Newfoundland, is dominated by contourite deposits. These are subjected to submarine landsliding as apparent on the surface (multibeam image to the left) and in the subsurface). Geoforce DTS Sparker profiles show that these failures occurred retrogressively. Coring the headscarps allows development of the stratigraphy and creation of synthetic seismograms. Comparison of the seismograms with full phase Geoforce sparker data shows that Heinrich layers produce a strong correlateable horizon. Mutlibeam data are compliments of the Nerieida program; A NAFO sponsored project supported by Spain and Canada to map the outer banks of the Grand Banks of Newfoundland. Huntec data were acquired by Campbell et al. (2011) on Hudson expedition 2011031.
48°30'N
C’
0 3 6 9 12 15 Kilometers
Below are two profiles of the same data crossing core site Pc2011031012. One is displayed as envelope of the trace and the other as full phase. Controlled source subbottom systems, such as Chirps, record data in this form as they do not recover useable phase information. The loss in resolution is readily apparent and comparison with core stratigraphy is much less certian. Full phase data allow comparison with detailed core stratigraphy, as shown below and to the right.
Synthetic Seismogram PC2011031-10
1300
1350
1400
B B’
1000
1050
48°25'N
48°20'N
A’’’
A’’ B’
A’
C
A B
C’
1100
1200
1300
1400
1500
0
5
10 PC2011031-12
0
5
10
Synthetic Seismogram
1450
10
12
8 km
2 km
C
900
1000
1100
0
200
400
600
800
PC2011031-10
1100
0
200
400
600
Density (g/cm3)
PC2011031-12
Impedance
Synthetic Seismic Trace
Mag. Susc. (SI)
Shear Strength (kPa)
1450 1550 1650 1750 1.6 1.8 2 2.2 2.42.4 2.8 3.2 3.6 4
velocity(m/s)
-100 0 100 1.5 2.5 8 12 16 20
45°50'W 45°45'W
45°40'W
45°35'W
1600 1200
1400 1500 1600 1700
velocity(m/s)
1.2 1.6 2
Density (g/cm3)
1.5 2.5 3.5
Impedance
-100 0 100
Synthetic Seismic Trace
0 10 20
Shear Strength (kPa)
0 100 200 300
Mag. Susc. (SI) Core stratigraphy is from Cameron et al (2014) and compliments to K. Jarrett for providing physical property data.
1100
A’’’ A 500
2.0
10 km
1200
5 km Headwall (100 m) 900
2500
1300
1400
1500
1600
Burial of debris flow
A’’
Debris Flow Deposit
A’ Slump
1000
1100
1200
2.0
10 km
2.5
3.0
Perspective- Looking south
75 m high escarpment
outcrop of units 1 and 2
This Geoforce DTS Sparker profile was acquired in ultra deep water off of the Laruentian Fan. It shows how the fan levees consist of MTD deposits,
3.5 3D seismic slice through the Barrington Submarine Landslide
bedforms escarpment buried
even on the very surface and shows details of the failure, even on its lower bounding surface (from
Water Depth 10 m
escarpment Normandeau et al., this conference volume). 2.25 10 km
350 m 5 km bedrock high recent failure deposits
W
bedrock
eroded seabed
multiple
50 ms twtt
2 km
135 m
165 m
stacked E failure deposits
4-5
3
6.5
6.75
Direction of Movement Erosional Groves
Emergence
Erosional Pit
4900
5000
5100
2.5
Geoforce DTS Sparker profile of the Scotian Slope, duplicating the 3D industry seismic profile shown above. These sparker data were migrated and plotted here as full phase. They show that, although the slump is reflected at the seafloor and looks relatively recent in bathymetry and on the industry seismic profile. The slump is buried by approximately 70 ms (50 m) of stratified sediment making it Pleistocene in age. (from Mosher and Campbell, 2006)
Geoforce DTS profile in a shallow water region (St. Lawrence River Estuary), showing multiple stacked MTDs (from Campbell et al., 2008)
20 km
Sea surface return multiple
Sea surface return
Depth (m
)
Depth (m
) D
epth (m)
Depth (m
)
Depth (m
)
Water D
ept (m)
Depth (m
)
Tim
e (m
s 2-
way
)
Tim
e (m
s 2-w
ay)
Trav
eltim
e (s
)
Tim
e (m
s 2-w
ay)
ms
- 2-w
ay
Tim
e (m
s 2-w
ay)
Bar
-met
res
Bar
-met
res
Tim
e (s
2-w
ay)
dept
h(cm
)
Pow
er S
pect
ral D
ensi
ty
Pow
er S
pect
ral D
ensi
ty
met
res
Tim
e (m
s 2-
way
) Ti
me
(ms
2-w
ay)
Tim
e (s
2-w
ay)
dept
h(cm
)