1. Final Report Due Friday 22 March 5:00 PM Format =paper
ESS135 Winter 2013 Review
Final Report Due Friday 22 March 5:00 PM
Format =paper

2. Final Report Abstract Introduction Experiments Results Discussion
Conclusions
Acknowledgments
Bibliography

5. As a first approximation the Earth has an ellipsoidal shape, wider at the equator.
A better approximation is the geoid (height) which measures the variation of shape relative to the ellipsoid. This variation is caused by mass heterogeneities

12. Snell’s Law
Consider the refraction of a plane wave at a plane boundary, as in Fig. 1. Each point in a wavefront may be regarded as a source for further propagation of the wave and the distance travelled in time dt is proportional to the wave speed, which is different in the two media, as illustrated. The angles i1 and i2 are related by considering the triangles ABC and ABD.
Thus
and
so that
This is Snell’s law of refraction.

13. Critical Refraction
Head waves are due to Huygen wavelets from the refracted wave in layer 2 that travel in layer 1
Note

14. Head waves up arrows direct wave and reflected waves

15. Head wave speed
Head wave travels along the surface at the same speed as the waves in layer 2

16. Travel Time Curves

18. Correction is t=DR/v1-DRv/v2

19. Moveout

20. Reflection Hyperbola

21. Multiple Layers assuming you have vrms

26. Magnetic Field
Horizontal and Vertical Components +

27. Field from a dipole - +
NOTE

28. 400 nT
800 nT

29. Theory r1 r2 V I r3 r4

30. VR
resistance V VL
Voltage in inductor
Leads voltage in
Resistor by 90 degrees
Total voltage leads
Current by Ф
Inductor V VL Ф VR

31. Steel at 6.9 meters distance?x h

32. Inducing field
Bocos(wt)
emf from Faraday’s law
Current=> BS IR
I L
emfT
Secondary field is less than 90+ degrees out of phase
With the primary inducing field.
Good conductor
Poor conductor

33. Magnetotellurics

34. Magnetotellurics Theory (After Telford et al.,)

35. Magnetotellurics Theory (After Telford et al.,)

36. Wires connected to the ground are used to measure E
Wires connected to the ground are used to measure E. A coil or magnetometer
measures H at right angles. The data is band pass filtered at frequency to
obtain apparent resistivity as a function of frequency. Then tomographic methods
Are used to image resistvity at depth – similar to the resistivity surveys we did.

37. The End
Good Luck