1. The Wave Equation Modeled
We’ve looked at what happens to P-waves in the simple two-layer case...

2. The Wave Equation Modeled
…we get a direct P-wave, a refracted P-wave, and a reflected P-wave.

3. The Wave Equation Modeled
So, you can now easily find the three P-wave phases:

4. The Wave Equation Modeled
…but, as you saw in your lab field data, real data adds the complication of other phases–here, the air wave and ground roll (Rayleigh wave) are shown.

5. Multilayer Model
Remember, for refraction data you generally only need to know the first arrivals…
Distance
Direct Wave
1st Layer Refraction
Time
2nd Refraction

6. Reflection/Refraction
Refraction Advantages:
Small number of sources/receivers can work
Little signal processing is needed
Interpretation straight forward
Reflection Advantages:
Small scale features can be resolved
No restriction on velocity-depth profile
Can be used in regions of complex geology
Uses entire reflected wavefield
Subsurface directly imaged

7. Seismic Reflection
Terms:
Stacked Section/Seismic Section: A plot of seismic reflection data with substantial digital processing that represents a zero-offset profile.
Time Section: A seismic section in which the axes are offset and two-way travel time. Rarely represent correct spatial positioning of subsurface features.
Depth Section: A seismic section in which the time section has been converted to depth through a velocity model.

8. Seismic Reflection Data
Processing Steps
Unlike refraction data, there are many
processing steps to create an image
of the subsurface with seismic
reflection data. Many of these are not
trivial, and we will look at some of
them in lab.
Poorly processed seismic data can
be made to look like just about
anything. You’ve been warned!

9. Seismic Reflection Data
The basis of common midpoint
(CMP) processing is to create a
stacked profile representing a
zero-offset section. CMP processing
is the current industry standard.

10. Seismic Reflection Data

11. Seismic Reflection Data

12. Seismic Reflection Data
Processing Problems…
Best Data Poorly Processed Data

13. Seismic Reflection Data
Examining Raw Data...

14. Seismic Reflection Data
Examining Raw Data…
Be aware that
seismic data is as
varied as geologic
settings, and thus can
look very different.

15. Seismic Reflection Data
Digital filtering
is a critical
processing
step...

16. Seismic Reflection Data
You data
can be analyzed in
other domains as well
as the frequency
domain.