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Environmental and Exploration Geophysics II

Environmental and Exploration Geophysics II. Magnetic methods. tom.h.wilson tom.wilson@mail.wvu.edu. Department of Geology and Geography West Virginia University Morgantown, WV. We’ll pick up with Magnetic Methods on Thursday. Magnetic polarity reversals on the sea floor provide.

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Environmental and Exploration Geophysics II

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

  2. We’ll pick up with Magnetic Methods on Thursday Tom Wilson, Department of Geology and Geography

  3. Magnetic polarity reversals on the sea floor provide Tom Wilson, Department of Geology and Geography

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

  5. Charged particles from the sun stream into the earth’s magnetic field and crash into the gasses of the atmosphere Tom Wilson, Department of Geology and Geography

  6. The Earth’s magnetic field http://www.windows2universe.org/physical_science/magnetism/earth_magnet_dipole_interactive.html Tom Wilson, Department of Geology and Geography

  7. Location of north magnetic pole Tom Wilson, Department of Geology and Geography

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

  9. Magnetic Fields – Basic Relationships 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 Tom Wilson, Department of Geology and Geography

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

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

  12. Magnetic Elements • three orthogonal strength components (X, Y, and Z); • the total field strength and two angles (F, d, i); or • two strength components and an angle (H, Z, d) http://gsc.nrcan.gc.ca/geomag/field/comp_e.php Tom Wilson, Department of Geology and Geography

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

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

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

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

  17. 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. Tom Wilson, Department of Geology and Geography

  18. Main field intensity Magnetic Intensity in Morgantown 11/15/2012 Total intensity = 52580nT Tom Wilson, Department of Geology and Geography

  19. Magnetic Inclination 11/15/2012 Inclination = 67.13o Tom Wilson, Department of Geology and Geography

  20. Magnetic Inclination Variations of inclination through time 11/15/2012 Inclination = 67.13o Tom Wilson, Department of Geology and Geography

  21. Magnetic Declination 11/15/2012 declination = -9.08o Tom Wilson, Department of Geology and Geography

  22. Variations of declination Magnetic Declination through time W Today, the compass points about 9 degrees west of GN Tom Wilson, Department of Geology and Geography

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

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

  25. Another site of interest http://spidr.ngdc.noaa.gov/spidr/ Tom Wilson, Department of Geology and Geography

  26. We are also interested in local induced magnetic fields Gochioco and Ruev, 2006 Tom Wilson, Department of Geology and Geography

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

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

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

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

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

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

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

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

  35. 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 - Tom Wilson, Department of Geology and Geography

  36. Magnetic Fields – Basic Relationships Magnetic monopoles p1 r12 Fm12Magnetic Force Magnetic Permeability p1and p2pole strengths Coulomb’s Law p2 Tom Wilson, Department of Geology and Geography

  37. Magnetic Fields – Basic Relationships Force Magnetic Field Intensity often written as H pt 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 (FE). Tom Wilson, Department of Geology and Geography

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

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

  40. To do list … • Hand in your paper summaries today • Hand in the gravity lab today. • Magnetic papers will be in the mail room tomorrow morning • Magnetic paper summaries will be due Tuesday, December 4th • The magnetics lab will be due December 6th. Stay tuned for specific instructions on this last lab report • Continue reading Chapter 7 – Tom Wilson, Department of Geology and Geography

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