STUDY QUESTIONS

 

 QUESTIONS ON SEISMIC

  1. Give a formula which relates wavelength and frequency.

  1. Distinguish between a seismograph and a seismogram.

  1. Explain in very simple terms how a seismograph works.

  1. What are the 4 principle types of waves produced by an earthquake?
    Which of these are body waves?
    Which are surface waves?

  1. Which waves are the fastest? Gives equations for the velocities of P-waves and S-waves.

  1. What is the most important factor in determining velocity in rocks?

  1. What are SV and SH waves?

  1. Why can't S-waves travel through liquid (give a mathematical proof)?

  1. Show mathematically why P-waves are faster than S-waves.

  1. Describe the motion of a particle of rock as each of the four principle seismic waves passes.

  1. What is the effect of depth of focus on the production of surface waves?

  1. What happens when a seismic wave meets a surface of discontinuity within the Earth?

  1. What is the relation between the angle of reflection and the angle of incidence?

  1. Give Snell's Law.

  1. What happens to a wave when it meets a surface of discontinuity at the critical angle?

  1. Be able to trace the paths of earthquake waves such as PS, PcS, PKP, PKIKP, pPcP, etc.

  1. List some reflected and/or refracted waves which might be mistaken on seismograms for surface waves and for aftershocks.

  1. Explain how the epicenter of an earthquake can be located.
     

  1. How do we know that the upper mantle is partially molten?

  1. At what depths do major discontinuities exist within the Earth? What are the names of these discontinuities?
    Name 2 minor discontinuities in the Earth.

  1. What are the two methods commonly used in seismic prospecting?
    Which is most often used? Which gives the most information?

  1. What sources of energy are most often used in seismic exploration?

  1. Describe in detail how refraction profiles would be produced, and what information could be obtained from them.

  1. What kind of time/distance graph would be produced where velocity increases continuously with depth?

  1. What kind of graph would be produced where velocity first increases continuously with depth and then abruptly changes?

  1. What kind of graph would be obtained if a seismic profile was taken perpendicular to the strike of a vertical fault?
    How can the throw of the fault be determined?

  1. List 3 factors which help determine seismic wave velocity.

  1. How does one recognize a reflecting horizon on seismograms?

  1. How can the depth to a reflecting horizon be determined?

  1. How can the dip of a reflecting horizon be determined?

  1. What is seismic/earthquake tomography? What information can it provide?

  1. List and discuss possible geophysical properties which may be indicators of forthcoming earthquakes.

  1.  Hooke's Law.

  • Define

  • stress

  • strain 

  • Young's modulus

  • Poisson's ratio

  • bulk modulus

  • compressibility

  • modulus of rigidity

  • Shear modulus

 QUESTIONS ON RESISTIVITY

  1. Define potential difference. What is the difference in potential difference and voltage? What is the unit of voltage?
  2. Define:
  1. What are the units for resistivity? Give a formula for resistance.
  2. What is the most important thing that determines conductivities of rocks?
  3. When a current is passed through the ground, what effects do bodies of different conductivity produce?
  4. How can you map the electric field produced when a current is passed through the ground?
  5. Define equipotential lines.
  6. What happens to equipotential lines in the presence of a good conductor? in the presence of a good insulator?
  7. How can you study vertical differences in resistivity in the Earth?
  8. Write a good original question to add to this list.

QUESTIONS ON GRAVITY

  1. What is the approximate value for the acceleration of gravity?
  2. How do we know that the interior of the Earth must be composed of rocks denser than those on the Earth's surface?
  3. What causes the Earth's oblateness?
  4. Define:
  1. What is the name of the formula used to calculate the theoretical value of "g" at any latitude?
  2. In what two ways may one measure the actual value of g at a particular location?
  3. What is a gravity anomaly? a positive gravity anomaly? a negative gravity anomaly?
  4. Name the reasons why the actual value of g measured at a particular place is not the same as the theoretical value.
  5. What corrections are applied to:
  1. Define:
  1. Which of the three most commonly applied corrections is the least important and is often ignored?
    If not ignored, how is the corrections usually made? Why is the topographic correction always added to the measured value?
  2. What are the characteristic values for Bouguer Anomalies in the following places?
  1. How are positive anomalies produced? negative anomalies?
  2. Describe Pratt's and Airy's concepts of isostasy. Which is probably correct?
  3. What is another name for small scale anomalies which remain after regional anomalies are removed?
  4. Outline the procedure for interpreting gravity anomalies.
  5. What kinds of anomalies (sign and shape) would be produced by the following geologic features?
  1. What is the "International Gravity Formula"? What does each term in the definition signify? Explain what the formula is used for.
  2. Define Free Air, simple Bouguer and complete Bouguer anomalies. What is the significance of each term in the definitions?
  3. Explain how the three anomalies behave on a regional scale and on a local scale. Which anomaly is preferred for exploration? Explain why.
  4.  Explain several ways to separate regional and residual gravity fields. What are the advantages and disadvantages of each method? In what circumstances would each be preferred?
  5.  Compare and contrast gravity methods with other geophysical methods for solving various problems such as...
  6.  Explain how to convert gravity meter readings into gravity anomalies relative to a base station. What data do you need in addition to the meter readings?
  7. Write a good original question to add to this list.

 

 QUESTIONS ON Oceanic Lithosphere

  1. What is the lithosphere?  How are its boundaries defined?  On what evidence is its existence based?

  2. How is sea floor topography inferred from studies of gravity over the ocean?

  3. Is Earth’s mantle beneath the plates liquid or solid? Explain.

  4. How deep are the deepest earthquakes at mid-ocean ridges? At transform faults? At subduction zones?

 

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updated January 5-2005