Seismic Reflection profiling

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• Seismic Reflection profiling
• Seismic system 3 components
• Source (sparker, airgun, watergun, boomer,
  dynamite,
• depth charges!!!)
• 2) Receiver (geophone, hydrophone streamers)
• 3) Recorders (paper records, tape recorder,
  digital receiver)
• 4) Navigation (Loran, GPS)

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Basic principles 1) Sound waves reflect off
interfaces back to receiver 2) What interfaces
A) rocks or sediments have 2 properties of
significance for seismic reflection-
1-velocity (sonic)-speed that sound
travels through medium
2-saturated bulk density-function of grains and
porosity as well as density of
rock B) Product of two components - v
? is acoustic impedance
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C) Amount of acoustic energy returned
is f (n) of rate of change of
impedance reflection coefficient
RC ?2v2 - ?1 v1
__________
?2v2 ?1 v1
Consequently
large changes in density or velocity should give
high amplitude reflectors-no change (or
contrast) gives no reflectors
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Travel time and vertical exaggeration 2-way
travel time- sonic wave travels through a medium
at a certain velocity, which is a property of
that medium. Generally the denser the material,
the higher the velocity Seismic data is recorded
as a function of the time it takes for the sonic
wave to travel through the medium, reflect offan
interface and return to the receiver. This is
known as 2-way travel time. This can only be
converted to depth (i.e. metres) if the velocity
structure is known-e.g. For water this
equation is xseconds x 1500m/sec

________________
2 Vertical
exaggeration immense on seismic records
Vertical axis in time horizontal axis is in shot
number which is a function of ship speed and
firing rate
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Artifacts
Multiples caused by
ringing inside two layers or high contrast
boundaries peglegs Bowties.

Details in the
handout from class Resolution
A
function of the wavelength (?) of the sound
wave-generally the resolution is half of the ? so
if the

wavelength is 1m then you can resolve a layer of
50cm. Descriptions
Continuity-
coherent/continuous incoherent/discontinuous

Amplitude- depends on density
contrasts between reflectors-if it is high then
you have a high amplitude

(strong) reflector

Frequency- generally frequency and ? are
related-high frequency is usually short ?

Relationships- stratigraphic principles
apply-use these relationships and echo traces to
interpret Interpretation

Produce isopach maps, combine in 3-D seismic
grids
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System For shipboard use
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Peg-legs and multiples
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3-D seismic fence diagram
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USGS Line 25 At least 4 DSDP/ ODP Legs Drilled
on This line
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Raw seismic
Line 25-parallel To slope edge
Interpreted seismic
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Line 25-across the slope
Raw seismic
Interpreted seismic
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High resolution Huntec seismic from the Scotian
Shelf
Oldest Quaternary section
Seabed surface
Holocene boundary
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Scotian Shelf section in 300m of water
Holocene sediments
Glacial sediments
Surface multiple