1. Seismic Reflection
3D seismic reflection image of the Nankai Subduction zone, Japan

2. Seismic Sources: Land Surveys
Many options! Hammer, weight-drop, dynamite, vibroseis
What frequencies are needed?
What energy level is needed (what distances do you need to cover)?
Image courtesy USGS

3. Seismic Sources: Marine Surveys
Historically, dynamite was used, but due to environmental concerns air guns are now used.
If internet access is available, supplement with youtube video examples
(Langhammer, 1994)

4. Source Signals
Land - Vibroseis Source
Marine – Airgun Source

5. Airgun array

6. Land Recording
Each recording point is a small array

7. Marine recording- hydrophones on a “streamer”

8. Random Noise Noise that is transient in space or time. Examples
Environmental noise (winds, swaying trees, wave noise, animals)
Electronic interference (portable equipment)
Human activity (traffic, people walking by, boat noise)
Quiet!
Seismic Equipment!

9. Coherent Noise
Signals that repeat on many traces and/or at different times that are not desired.
Typically represents a long-term feature or type of wave.
Examples:
Ground roll
Multiples
Electronic interference (power lines)

10. Does this reduce coherent
Stacking
Stacking is the summation of recorded waveforms/seismograms/traces that reflected off of the same point.
Does this reduce coherent
or random noise?
Duplicate records helps us raise the signal-to-noise ratio, giving us clearer images and improved resolution.
Here, we are looking at a Common Mid-Point Gather (CMP Gather).

11. Stacking
Stacking is simply adding & normalizing multiple traces or seismograms.
Constructive Interference
Destructive Interference + + =

12. Gathers – how to organize the data

13. Normal Moveout

14. Normal Moveout
t2(x) = to2 + x2/v2

15. Now these traces can be stacked to reduce noise!
Normal Moveout
t2(x) = to2 + x2/v2
Now these traces can be stacked to reduce noise!

16. Velocity Analysis
Ecker et al. 2000,1998