1. Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics I tom.h.wilson tom.wilson@mail.wvu.edu Department of Geology and Geography West Virginia University Morgantown, WV Magnetic Methods (I)

2. Tom Wilson, Department of Geology and Geography -0.5 0 Max = Min ~ sign Residual Separation Problem 6.3 – F-Ring Correction …. -16.3

3. Tom Wilson, Department of Geology and Geography Questions about Problems 6.3 – 6.5? 6.5 Radius of the smallest equidimensional void 6.8 Extract and interpret 0

4. Tom Wilson, Department of Geology and Geography 6.8 Extract residual and evaluate Right click and add trendline including the trendline equation If needed I can take a few minutes at the end of class to illustrate

5. Tom Wilson, Department of Geology and Geography Problem 6.9

6. Tom Wilson, Department of Geology and Geography On a more local scale, consider the ocean surface... Is the ocean surface a flat surface?

7. Tom Wilson, Department of Geology and Geography Map of the ocean floor obtained from satellite radar observations of ocean surface topography. SeaSat

8. Tom Wilson, Department of Geology and Geography Locating Trench Boundaries Theoretical model Examination of trench for internal magnetic anomalies. actual field data Gilkeson et al., 1986

9. Tom Wilson, Department of Geology and Geography Trench boundaries - field data Trench Boundaries - model data Gilkeson et al., 1986

10. Tom Wilson, Department of Geology and Geography From Martinek Abandoned Wells

11. Tom Wilson, Department of Geology and Geography From Martinek Abandoned Well - raised relief plot of measured magnetic field intensities

12. Tom Wilson, Department of Geology and Geography Locating abandoned wells

13. Tom Wilson, Department of Geology and Geography Gochioco and Ruev, 2006 Using the GEM 2 to locate abandoned wells

14. Tom Wilson, Department of Geology and Geography Falls Run Coal Mine Refuse Pile Magnetic Intensity Wire Frame

15. Tom Wilson, Department of Geology and Geography Data Acquisition

16. Tom Wilson, Department of Geology and Geography Magnetic and terrain conductivity responses over the refuse area

17. Tom Wilson, Department of Geology and Geography Magnetic monopoles p1p1 p2p2 r 12 F m12 Magnetic Force  Magnetic Permeability p 1 and p 2 pole strengths Coulomb’s Law Magnetic Fields – Basic Relationships

18. Tom Wilson, Department of Geology and Geography Force Magnetic Field Intensity often written as H p t is an isolated test pole The text uses F instead of H to represent magnetic field intensity, especially when referring to that of the Earth (F E ). Magnetic Fields – Basic Relationships

19. Tom Wilson, Department of Geology and Geography The fundamental magnetic element is a dipole or combination of one positive and one negative magnetic monopole. The characteristics of the magnetic field are derived from the combined effects of non-existent monopoles. Dipole Field Magnetic Fields – Basic Relationships

20. Tom Wilson, Department of Geology and Geography monopole vs. dipole Toxic Waste Magnetic Fields – Basic Relationships

21. Tom Wilson, Department of Geology and Geography The earth’s main magnetic field

22. Tom Wilson, Department of Geology and Geography Steve Sheriff’s Environmental Geophysics CourseEnvironmental Geophysics Proton Precession Magnetometers Tom Boyd’s Introduction to Geophysical Exploration CourseIntroduction to Geophysical Exploration Measuring the Earth’s magnetic field water kerosene & alcohol

23. Tom Wilson, Department of Geology and Geography Source of Protons and DC current source Proton precession generates an alternating current in the surrounding coil Magnetic Fields – Basic Relationships

24. Tom Wilson, Department of Geology and Geography Proton precession frequency (f) is directly proportional to the main magnetic field intensity F and magnetic moment of the proton. L is the angular momentum of the proton and G is the gyromagnetic ratio which is a constant for all protons (G = M/L = 0.267513/  sec). Hence -

25. Tom Wilson, Department of Geology and Geography Magnetic Elements

26. Tom Wilson, Department of Geology and Geography Magnetic Elements

27. Tom Wilson, Department of Geology and Geography Magnetic Elements

28. Tom Wilson, Department of Geology and Geography Magnetic Elements

29. Tom Wilson, Department of Geology and Geography Magnetic north pole: point where field lines point vertically downward Geomagnetic north pole: pole associated with the dipole approximation of the earth’s magnetic field. The compass needle points to the magnetic north pole.

30. Tom Wilson, Department of Geology and Geography Magnetic Intensity

31. Tom Wilson, Department of Geology and Geography Magnetic Inclination

32. Tom Wilson, Department of Geology and Geography Magnetic Inclination

33. Tom Wilson, Department of Geology and Geography Magnetic Declination

34. Tom Wilson, Department of Geology and Geography W Magnetic Declination

35. Tom Wilson, Department of Geology and Geography Magnetic Elements for your location http://www.ngdc.noaa.gov/geomagmodels/struts/calcPointIGRF

36. Tom Wilson, Department of Geology and Geography Today’s Space Weather http://www.swpc.noaa.gov/today.html Magnetic Elements http://www.ngdc.noaa.gov/geomag/magfield.shtml

37. Tom Wilson, Department of Geology and Geography Anomaly associated with buried metallic materials Bedrock configuration determined from gravity survey Results obtained from inverse modeling Computed magnetic field produced by bedrock Introduction to the magnetics computer lab

38. Tom Wilson, Department of Geology and Geography Where are the drums and how many are there?

39. Tom Wilson, Department of Geology and Geography Turn in gravity lab today. Turn in Part 2 (problems 3-5) of gravity problem set 3, Tuesday, November 18 th.