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
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
Applications for Refraction seismic
• Depth of groundwater level
• Depth and location of hardrock
• Elastic medium parameters
• Glaciology
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
t
x
v
Velocity of direct wave is derived from the distance and travel time
o x x x x
t 1v---x=
v xt---=
Direct wave
Reflection: Horizontal reflector
t0
for x=0:
t(x=0)=t0=2h/v
t2v2=4h2
or
h=t0v/2
t2v2=4h2+x2
t2= x2/v2+t02
h
Reflection: horizontal reflector
t2v2 - x2 = 4h2
t2v2 = 4h2+x2
Hyperbola
t2v2
4h2 4h2x2
- =1
x>>h vxt =
h
90+
h
h
x
t2v2=4h2+x2- 4hxcos(90+)
t2v2=4h2+x2+4hxsin()
Hyperbola:
t2v2
[2hcos()]2 [2hcos()]2
[x+2hsin()] 2
- =1
-x x
X=-2hsin
Tdip
Tdip= tx-t-x =v
2xsin
v1
x
v2
ti
t xv2-----
2h 22
v12
–
v1v2--------------------+=
h
txv2-----t i+=
xcros 2hv2 v1+
v2 v1–------------=
xcrossx
t1v2-----
Refraction: horizontal reflector
v
1v1
-----
Huygens’ Principle:
Every point on a wavefront can be considered as a secondary source of spherical waves
Reflection/Diffraction
Reflection
t0=2h/v
tr t0+t
t =x2/(4vh)
td t0+2t
/Diffraction
Reflection:
Diffraction:
h