1. 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

2. Geometrical situation
Direct wave
Refracted wave
Reflected wave

3. Traveltime curve

4. Receivers
Source
Receivers

5. Velocity of direct wave is derived from the distance and travel time1 v
--- x = x x x x x v x t
--- = o v
Velocity of direct wave is derived from the distance and
travel time

6. Refraction seismic

7. Direct wave
Refracted wave
Reflected wave

8. Traveltime curve

9. Interpreting first arrivals
Direct arrivals from Layer 1
Refracted arrivals from Layer 2
The different arrival times and the rates at which the first arrivals come in are used to make interpretations of the depth to the different subsurface layers.
Image obtained on 8/12/2005 from

10. h

11. Refraction: horizontal reflector1 1
----- v
----- 1 v 2 2 2 2h v – v x 2 1 t =
----- + v v v t 2 1 2 i x t =
-----t + x v i x 2
cross x h v + v x = 2h 2 1
cros v – v v 2 1 1 v 2

13. For small slopes ( < 100):

14. For small slopes ( < 100):

15. Surface
800 m
V=1.6 km/s

16. Reflection/Diffraction
t0=2h/v
tr t0+dt
dt =x2/(4vh) h
/Diffraction
Reflection
Diffraction:
td t0+2dt

17. Source
Receivers
Receivers x t
Direct wave
Reflected wave layer 1/2
Refracted wave layer 2/3
Reflected wave layer 2/3
Refracted wave layer 1/2

18. West
East

19. West
East

20. East
West

21. West
East

22. West
East

23. West
East

24. East
West