1. Environmental and Exploration Geophysics I tom.h.wilson tom.wilson@mail.wvu.edu Department of Geology and Geography West Virginia University Morgantown, WV Magnetics Lab Discussions

2. Anomaly associated with buried metallic materials Bedrock configuration determined from gravity survey Results obtained from inverse modeling Computed magnetic field produced by bedrock

3. Where are the drums and how many are there?

4. Part 1: 1. The magnetic field intensity of a dipole is given as Offer a mathematical argument to show that the field intensity near one end of a long magnetic dipole (for example that produced by well casing) is nearly equal to that of an isolated magnetic pole. r- and r+ refer to the distances from the point of observation to the negative and positive poles of the dipole, respectively. p denotes the pole strength. Hint: one of the poles will be at a much greater distance from the surface than the other. Draw a diagram. Show your work. Make a statement of the conclusion.

5. 2. In reference to the figure below, determine the pole strength in ups (unit pole strength) given that the magnetic field intensity at the point of observation is 500 nT. (Note that the 500nT value is the magnitude of a vector.) 20cm 40cm Observation point -+

6. Work backwards from the resultant vector dipole field intensity to the field intensity produced by a single pole (Hint: look at the layout in the above diagram). Then, determine the pole strength in ups (recall 1 Oersted =105 nT, and 1 ups equals 1 Oersted-cm2). Reproduce discussions in class that result in value of H+ and H-. Once you have H (+ or -; the magnitude will be the same for either), show how you get the pole strength p in ups. Show steps. State final result and conclusion. 20cm 40cm Observation point -+

7. What does this tell us about units of these different quantities? We refer to the magnetic field intensity as H or, more ambiguously, as F

8. Continue your reading of Chapter 7 and consider problems 7.1, 7.3, and 7.7. The next and final problem set (handed out this Thursday) will consider problems similar to the above.