presentation chapter 4: interpretation of raw seismic records
TRANSCRIPT
Overview ta3520Introduction to seismics
• Fourier Analysis• Basic principles of the Seismic Method• Interpretation of Raw Seismic Records• Seismic Instrumentation• Processing of Seismic Reflection Data• Vertical Seismic Profiles
Practical:• Processing practical (with MATLAB)
The seismic record
Body waves:
Surface waves:
A seismic shot record on land
Linear event:Direct/refraction
Linear event:Slower, Direct
Slightly hyperbolicevent: Reflection
Linear event:Very slow, Direct
Interpretation of seismic land record
thic
kn
ess 2
00
m
source detector
offset
air wave
surface wave(velocity 1850 m/s)
refraction
velocity 340 m/s
velocity 3500 m/s(P waves)
velocity 4800 m/s
Modelling of seismic land record
Observed data Modelled data
(ray theory approx.)
refraction
direct P-wave
surface wave
reflection
reflection
direct air wave
A seismic shot record at sea
Linear event:Refraction
Many Hyperbolic events: Reflections
Linear event: Direct
First hyperbolic event: primary reflection
Hyperbolic event at twice timeof primary reflection: multiple
Interpretation of marine record
30
0 msource detecto
r
offset
direct P wave
refraction velocity 240 m/s
velocity 1500 m/s(P waves)
velocity 1500 m/s(density different)
25
0 m
reflection
multip
le
reflection
Modelling of marine record
Observed data Modelled data
(ray theory approx.)
refractiondirect P-wave (water)
reflectionsmultiple reflectionmultiple reflection