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 (V) and Exam Review session 1

2. On tap for the day Tom Wilson, Department of Geology and Geography Just a reminder to hand in the pole strength problem (done in class the Thursday before Thanksgiving break) and Tuesday’s group problems (these count 20 points - total) Group problems are posted on the class page. I also have copies raise hand if you want one. Review and discuss solutions Review material for the exam Your questions Example test questions for take-home study Hand in problems 7.1-3 and 4 & 5 before leaving or put in my mail box this afternoon (these count 50 points)

3. Breakout problems > Group 1 Tom Wilson, Department of Geology and Geography

4. Each group had one of these source geometry evaluation problems Tom Wilson, Department of Geology and Geography

5. In each case, you start by noting diagnostic positions along the anomaly profile Tom Wilson, Department of Geology and Geography

6. For group 1 Tom Wilson, Department of Geology and Geography 1.25 2.05 2.9 Sphere or vertical cylinder? Depth?

7. For groups 2 and 3 Tom Wilson, Department of Geology and Geography Group 2: cylinder – 10km Group 3: cylinder – 10km

8. Group 2 – problem 1 Tom Wilson, Department of Geology and Geography

9. Problem 1 Tom Wilson, Department of Geology and Geography In the class problem set handout, the depth z was set equal to 1.9m. Think about the rationale involved in deciding on the depth to the center of the cylindrical approximation of the wall. Using 1.9m we get Z max =4.3nT. Using 1.75m, we get 5.46 nT. Although a minor difference, which do you think yields the better approximation? Neither anomaly would be detectable above a background noise level of ±5nT. Actually worked for you in the problem set handout. z in either case represents depth to center!

10. If you double the depth, the anomaly amplitude drops by … Tom Wilson, Department of Geology and Geography At a depth of 1 meter Z max is 29.26. At a depth of 2 meters Z max is 3.66. Z max varies inversely as the cube of the depth. If the depth is doubled, Z max will decrease to one-eighth of its former value.

11. Group 3 – problem 1 Tom Wilson, Department of Geology and Geography The first question usually asked before beginning a geophysical investigation of any kind is “Will this method provide the information I want?” That usually means “Can I detect the object(s) I want to find?” R=1m Z=3m Burial Chamber Relative susceptibility contrast =-0.0001emu. Surface

12. And here? Tom Wilson, Department of Geology and Geography

13. The anomalies in group problems 2 and 3 Tom Wilson, Department of Geology and Geography hold another lesson: where is 0?

14. Problem 2 – groups 2 and 3 Tom Wilson, Department of Geology and Geography

15. General review problems – see handout Tom Wilson, Department of Geology and Geography

16. Problems 2 and 3 are similar Tom Wilson, Department of Geology and Geography

17. 4 & 5 … Tom Wilson, Department of Geology and Geography

18. Look over the remainder of these problems for next time – see if you have any difficulties Tom Wilson, Department of Geology and Geography And bring questions to class!

19. Bring a pencil, ruler, eraser and calculator Show your work! Tom Wilson, Department of Geology and Geography I will hand out an equation list. It will look something like that posted on the class page. See http://pages.geo.wvu.edu/~wilson/geol454/equationlist.pdf Or access from link on session 30.

20. For now, let’s get started on three group problems – Problem 1: Tom Wilson, Department of Geology and Geography

21. Problem 2: Underground storage tank or missile silo. See diagnostic relationships Tom Wilson, Department of Geology and Geography

22. Another – gravity vs mag Tom Wilson, Department of Geology and Geography

23. Just some reminders Tom Wilson, Department of Geology and Geography Remember - hand in the pole strength problem (done in class the Thursday before Thanksgiving break) and Tuesday’s group problems. (these count 20 points) ALSO - Hand in problems 7-1 through 7-3, 4 & 5 before leaving or put them in my mail box. We will go over them next Tuesday Bring your questions to class for a final review session, next Tuesday, December 9 th. Work over the group problems and general review problems. We will review these at the start of next Tuesday’s session. Final is from 11am-1pm on Tuesday, December 16 th.