PHYS/GEOL 406 Homework
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   Homework #1: Due Friday January 30 by 5:10pm Reading:
  • Chapter 1 (yes, it's short, but note the advantages as well as the limitations of using geophysical methods)
  • Chapter 6 up until the end of section 6.3.3.
  1. Consider a gravity survey that is to begin at a base station whose latitude is 42° 37' 27''N; the radius of Earth at this location is 6,368.38km. What is gravity on the geoid (not at this elevation) at this latitude? Express your final answer twice, once in units of cm/s2 as well as in mgal.
  2. By how much would your answer change if you were to move 565.0m to the south of where you are located.
  3. Your company wants you to do a gravity survey with a gravimeter that can measure down to 0.03mgal. What is the maximum distance in meters north (or south) for a gravity survey line that would not require you to do a latitude drift correction for your data? For simplicity, assume you are in Radford, with φ=37.14°.
  4. Find the theoretical difference in gravity 'dg' from the first floor of Reed Hall to the third floor. The floors are 4.0m high. Earth's mass is 5.976x1024kg. Assume Earth's radius at sea level here is 6,370.38km, and that the first floor of Reed is 558.0m above sea level.
  5. A big-box store thinks there may be a void under their floors caused by the extensive karst in the area. You come in and measure a gravity anomaly of 0.09mgal over the presumed location of this void. Other geophysical methods reveal the top of the anomaly is 0.50m below the surface, and the anomaly itself has a radius of 2.6m. The background matrix has an average density of 2,670kg/m3. If the void is filled with air, then it could easily be pumped full of sand/concrete. If the void is filled with water then that's a problem since that water has a source and could be making the void larger by the minute. Determine whether this void is filled with air or water by (a)calculating a relevant number, and then (b) explaining how that number lets you determine your answer.
   That's all for homework #1.