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 Intro to magnetic methods

2. Tom Wilson, Department of Geology and Geography The Earth’s magnetic field

3. Magnetic polarity reversals occur on average about 4 to 5 times per million years Tom Wilson, Department of Geology and Geography

4. Location of north magnetic pole Tom Wilson, Department of Geology and Geography http://www.compassdude.com/compass-declination.shtml

5. The Earth’s magnetic field is also very dynamic on short time scales Tom Wilson, Department of Geology and Geography Charged particles from the sun stream into the earth’s magnetic field and crash into the gasses of the upper atmosphere

6. Tom Wilson, Department of Geology and Geography Protons and electrons in the solar wind crash into earth’s magnetosphere.

7. Comet ISON has two tails! Tom Wilson, Department of Geology and Geography

8. Field surveys Tom Wilson, Department of Geology and Geography

9. Making measurements of the Earth’s magnetic field 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 Water, kerosene & alcohol

10. 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

11. Tom Wilson, Department of Geology and Geography Proton precession frequency (f) is directly proportional to the main magnetic field intensity F and magnetic dipole moment of the proton (M). 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 -

12. Locate trench boundaries and map distributions of metallic debris Tom Wilson, Department of Geology and Geography Theoretical model Examination of trench for internal magnetic anomalies. actual field data. Gilkeson et al., 1986

13. Abandoned wells Tom Wilson, Department of Geology and Geography From Martinek

14. Tom Wilson, Department of Geology and Geography Gochioco and Ruev, 2006 We are also interested in local induced magnetic fields produced by metallic objects Where are the abandoned wells?

15. Anomalous fields from abandoned wells often produce large distinctive anomalies Tom Wilson, Department of Geology and Geography Locating abandoned wells

16. Raised relief display Tom Wilson, Department of Geology and Geography From Martinek raised relief plot of measured magnetic field intensities

17. Measurement of different field components: total, vertical and horizontal gradients Tom Wilson, Department of Geology and Geography

18. Test site Tom Wilson, Department of Geology and Geography

19. Results of field tests Tom Wilson, Department of Geology and Geography

20. 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

21. 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

22. Magnetic fields – basic relationships 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

23. Tom Wilson, Department of Geology and Geography monopole vs. dipole Toxic Waste Magnetic fields – basic relationships

24. The Earth’s main magnetic field Tom Wilson, Department of Geology and Geography

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

26. 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. Magnetic field intensity in Morgantown, WV Tom Wilson, Department of Geology and Geography The drop is associated with the westerly rotation of the earth’s magnetic field.

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

32. Magnetic inclination in the Morgantown area Tom Wilson, Department of Geology and Geography westerly rotation of the earth’s magnetic field produces the current decrease in inclination

33. Magnetic declination Currently the compass point west of true north Tom Wilson, Department of Geology and Geography

34. Magnetic declination and its variation through time Tom Wilson, Department of Geology and Geography West declination is negative

35. Tom Wilson, Department of Geology and Geography Magnetic Elements for your location http://www.ngdc.noaa.gov/geomag-web/#declination

36. Magnetic elements Tom Wilson, Department of Geology and Geography 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. Let’s get started Tom Wilson, Department of Geology and Geography Where are the drums and how many are there?

39. Tom Wilson, Department of Geology and Geography Items on the list …. Gravity paper summary(s) (both sections) due today, Nov. 14th Gravity lab will be due on Thursday November 21 st (writing section submission is self-reviewed showing track changes). Gravity lab – last chance for questions this coming Tuesday Keep reading Chapter 7. We will have two final exam review sessions: December 5 th and December 10 th. Final is from 3-5pm on December 13 th.

40. Regular section submissions Tom Wilson, Department of Geology and Geography All those in the regular section submit paper copies of your paper summaries and lab reports.

41. Writing Section reminders (electronic submissions only) Tom Wilson, Department of Geology and Geography Revised paper summary 1 and self-reviewed paper summary 2 are due today. The gravity lab is self reviewed and is due on Thursday, November 21 st. All those in the writing section submit their papers and lab electronically. Don’t forget to turn on track changes while doing your self- review. Only submit the self-reviewed file.

42. What’s coming up? Some due date reminders Tom Wilson, Department of Geology and Geography