1. Seismogram Relation between seismic trace and geology Wavelets
Multiples
Resolution
Vertical resolution
Horizontal resolution

2. Seismogram of an earthquake mid atlantic ridge measured in Brasil magnitude 5 (sept 2002) 3000km
Amplitude
Unfiltered:
Time (s)
Filtered: P PP
PcP S SS
Rayleigh

3. From geology to seismogram

4. Waves Amplitude t or x Wavelength l Period t Phase 1 2 p Period t ==
---
------ f w
Wavelength l
Period t
Phase 2 p
Wavenumber k =
--- l
Velocity v = f× l

5. Important wave forms
Zero-Phase
Minimum Phase
0 time
0 time

6. Minimum phase and zero-phase wavelet
Minimum phase wavelet:
Zero phase wavelet:
Energy is maximally front-loaded
(Energy does not arrive before zero time)
Symmetric with respect to zero time
and peaks at zero time
(Energy arrives also before zero time)

7. Important waveforms
Minimum Phase
Zero Phase

8. Display of Seismogram

9. Example of a shot
Reynolds, 1997

10. Multiples

11. Air gun record
Keary and Brooks

12. Surface
Riverbed
Sediment
Bedrock
Reynolds

13. Resolution
Resolution refers to the minimum separation between two features such that we can tell that
there are two features rather than only one.
Vertical resolution
Horizontal resolution

14. Comparison of resolution of different data sets
30 Hz wave
gamma log
Big Ben (ca. 123 m)
at 2000 m/s
through oil field
(Emery and Myers)

15. Vertical resolution Rayleigh’s-criterion:
Vertical resolution depends on:
- Frequency
- Velocity

16. Resolution of two boundaries depends on wavelength

17. l/4=12 ms V1 V2 V3
<
> or
R12
R23
R12/R23= pos. V3 V1 V2
<
> or
R12
R23
R12/R23= neg.

18. Horizontal resolutionw
for z>>l

19. Sampling theorem At least two samples per (horizontal) apparent
wavelength must be obtained in order to recognize
Features (remember the time sampling theorem!!).
For example, to recognize a stream channel on a
horizontal slice generally requires bin sizes no larger
than 1/3 or ¼ the channel width.