Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics I tom.h.wilson Department of Geology and Geography West Virginia University Morgantown, WV Final review session - II

Practice exam Tom Wilson, Department of Geology and Geography

The plate and the donut hole Tom Wilson, Department of Geology and Geography

Breaking it down by parts Tom Wilson, Department of Geology and Geography

Terrain effects Tom Wilson, Department of Geology and Geography 2. Calculate the acceleration due to a ring with inner radius of 457 meters, outer radius of 680 meters and thickness of 386 meters.

Tom Wilson, Department of Geology and Geography 4. You are given the main magnetic field intensity (F E ), the declination (d) and the horizontal projection of F E : H E. What is the vertical component of the earth’s magnetic field? What is the inclination of the main magnetic field? 5. You are standing 10 feet from a point directly over the end of abandoned casing string. The top of the abandoned well casing lies 10 feet beneath the surface. The effective pole strength for the casing string is 5 ups. What is the vertical component of the anomalous field at the observation point? State your answer in nanoTeslas. From the practice final …

State your answer in nanoTeslas Tom Wilson, Department of Geology and Geography 10’ p= 5 ups HEHE Remember 1 ups/cm 2 = Oersted and 1 Oersted = 10 5 nT You should get H v =1.9 nT Don’t forget to convert feet to cm! 14.4’ You should get H=2.69 nT

Tom Wilson, Department of Geology and Geography At 8 am you start your gravity survey at Base Station 5 in your survey area. You set out to establish another base station (Base Station 6) about an hours drive from Base 5. At 8am the acceleration due to gravity at Base Station 5 is 5.3 milliGals relative to the main base station in your survey area. You make it to the new base station and take a measurement 53 minutes after making the Base 5 observation. Your reading at Base Station 6 is 4.3 milliGals. You return to Base 5 but stop for gas along the way. You finally re-measure the Base 5 acceleration at 10 am (120 minutes after your initial measurement). The reading at Base Station 5 dropped 2 milliGals during that 120 minute period. What is the acceleration at Base Station 6 relative to the main base? Problem 6 – practice final > Tide & Drift.

Tom Wilson, Department of Geology and Geography Problem 7. Another problem that can be addressed using simple geometrical analysis

Tom Wilson, Department of Geology and Geography Diagnostic positions Multipliers Sphere Z Sphere Multipliers Cylinder Z Cylinder X 3/4 = X 1/2 = X 1/4 = Repeat of a familiar analytical approach H 3/4 = 161 H 1/2 = 108 H 1/4 = 54

Tom Wilson, Department of Geology and Geography 8. What is the theoretical gravity. 9. Write out the equation that defines the theoretical gravity 10. What is the terrain corrected Bouguer anomaly? 11. Given F E, H E, and d solve for Y E, X E, Z E and i. Some general questions ….

Missile silo or buried storage tank Tom Wilson, Department of Geology and Geography Diagnostic positionsMultipliers Sphere Z Sphere Multipliers Cylinder Z Cylinder X 3/4 = 4.7 meters X 1/2 = 7.7meters21.31 X 1/4 = 12.5 meters ~15m 15.4 ~ m 10.1

Tom Wilson, Department of Geology and Geography Turn in the magnetics paper reviews today Those in the writing section turn in last writing assignment tomorrow by noon Writing section paper summaries are also due to day Exam, Tuesday December 13 th ; 3-5pm