Reflected, Refracted and Diffracted waves

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Reflected, Refracted and Diffracted waves

• Reflected wave from a horizontal layer
• Reflected wave from a dipping layer
• Refracted wave from a horizontal layer
• Refracted wave from a dipping layer
• Diffracted waves

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Applications for shallow high resolution
Reflection seismic

• Hydrogeological studies of acquifers
• Engineering geology
• Shallow faults
• Mapping Quaternary deposits
• Ground investigation for pipe and sewerage tunnel
  detection

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Applications for Refraction seismic

• Depth of groundwater level
• Depth and location of hardrock
• Elastic medium parameters
• Glaciology

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• Refraction seismic
• Refracted Waves
• Mainly horizontal Wave propagation
• Only refracted waves are used. (Lower layer must
  have higher velocity than upper layer)
• Distribution of velocity as well as the depth
  and orientation of interfaces between layers
• Reflection seismic
• Reflected Waves (Echo lot principal)
• Mainly vertical wave propagation
• Complete seismic recording is used
• Distribution of the velocity variation

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Geometrical situation
Direct wave
Refracted wave
Reflected wave
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Traveltime curve
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Receivers
Source
Receivers
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Direct wave
t
x
x
x
x
x
o
v
Velocity of direct wave is derived from the
distance and travel time
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Reflection Horizontal reflector
o
x
s
h
s
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Reflection Horizontal reflector
t
0
h
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Reflection horizontal reflector
h
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Moveout
1
2
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Normal Moveout
1
0
0
1
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-x
x
x
90?
h
?
h
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Refraction seismic
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Propagation of seismic waves
(Roth et al., 1998)
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Direct wave
Refracted wave
Reflected wave
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Traveltime curve
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h
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Refraction horizontal reflector
t
1
1
-----
-----
v
v
1
2
2
2
2h
v

v
x
2
1
t
-----
--------------------


v
v
v
2
1
2
t
i
x
t
-----t


x
i
v
2
x
cross
x
h
v
v

2
1
x
2h
------------

cros
v
v

v
2
1
1
v
2
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Huygens Principle
Every point on a wavefront can be considered as a
secondary source of spherical waves
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Surface
800 m
V1.6 km/s
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Reflection/Diffraction
Reflection
h
Diffraction
td? t02dt
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Receivers
Direct wave
Reflected wave layer 1/2
Reflected wave layer 2/3