Geophysics 3413 - Principles of Geophysics

Course Description

3413 Principles of Geophysics. Prerequisite: Mathematics 2423; Physics 2524; or equivalent or permission. A survey of current methods of geophysical measurements and their interpretations. The earth's gravity, magnetic, seismic, mechanical and thermal properties will be discussed. (Sp)

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Judson L. Ahern
Office Hours: Energy Center Tower Room 924, by appointment
Contact: 325-4480,


Homework sets: 10  2  20
Tests 1 and 2  20  40
Test 3 30 30
Quizzes    10
 Total  100


Mostly open-notes problems, some closed-notes short questions. Exams are over material covered since last exam (i.e., no comprehensive final). Third exam on scheduled final exam day.


Wednesday, January 20 First Day of Classes
Wednesday, March 4, 2009 Exam 1 (see below)
Saturday, March 14 - March 22, 2009 Spring Break
Wednesday, April 8, 2009 Exam 2 (see below)
Friday, May 8 Last Day of Classes
Thursday, May 14, 2009, 8-10 AM Final Exam (see below)

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Text (See also References)

Fundamentals of Geophysics, William Lowrie, Cambridge University Press, 1997.

*on reserve, Geology Library

Note: "The University of Oklahoma is committed to providing reasonable accommodation for all students with disabilities. Students with disabilities who require accommodations in this course are requested to speak with the professor as early in the semester as possible. Students with disabilities must be registered with the Office of Disability Services prior to receiving accommodations in this course. The Office of Disability Services is located in Goddard Health Center, Suite 166, phone 405/325-3852 or TDD only 405/325-4173.

Some possible Test 1 questions/problems (neither limited to nor inclusive!):

Closed book, closed notes: mass of Earth; radius of Earth; Kepler's laws, in words; density of ocean and continental crust, mantle; Earth's oblateness, as a fraction and as a per cent; g(r) for point mass or radially symmetric body; U(r) for point mass or radially symmetric body;

Problems: orbital radius vs. period problem; planetary surface surface temperature problem; computing g from U; computing U (or delta U) from work done against g; escape velocity problem; g(r) inside homogeneous planet; g(r) outside an infinite cylinder;

Some possible Test 2 questions/problems (neither limited to nor inclusive!): As of 4/6/2009, for test on April 8, 2009

Closed book, closed notes: Be able to convert from m/s2 to mgals, µgals, without a calculator (it's moving a decimal point); what is the difference between absolute and relative gravity - why do we need both? What is the difference between a stable and an unstable mass-spring system (gravimeter)? Which do we use? What are the two ways normally used today to remove tidal variation in gravity? Define the Standard Bouguer Anomaly in terms of observed gravity and the various corrections (numbers not necessary - what corrections need to be made?). How do filtering, smoothing, upward/downward continuation, derivatives help us interpret a gravity profile or map? What is the uniqueness or ambiguity problem in gravity (geophysics)?

Problems: For a simple mass on a spring, how much would an x meter long spring change due to a y mgal change in g? Drift correction problem; latitude, free-air, Bouguer correction problem(s); Total error due to dependent and independent contributing errors; Given a gravity profile, draw a (qualitative) corresponding second-derivative anomaly profile below it.

Some possible Test 3 questions/problems (neither limited to nor inclusive!):

Closed book, closed notes: Magnetics: Similarities between grav and mag; differences between grav and mag; What are the three parts of the Earth's total magnetic field - describe briefly; difference between N & S mag poles for best-fit dipole vs. N dip pole and S dip pole;

Closed book, closed notes: Seismic: What is the P-wave shadow zone? where does it occur? what causes it? What is the S-wave shadow zone? where does it occur? what causes it?  Snell's law, general case, reflection, refraction, mode conversion; plane-wave velocity of P waves, S waves; Can there be a reflection between two layers but no refraction? How? Can there be a refraction between two layers but no reflection? How? Can there be a reflection and a refraction between two layers? How?

Problems: Magnetics: Convert between |FT|, D, i, X, Y, Z, H. Find inclination of the magnetic field  for a dipole field for a given magnetic colatitude. What is the strength of the total magnetic field for a dipole field at a given magnetic colatitude (in terms of, say, B0). Assume that the Earth's magnetic field is a dipole. At what distance above the Earth's surface is the magnitude of the field a given fraction of its value at the surface?

Problems: Seismic:  Find velocities and depths from refraction survey data for two layers on a half-space. Find velocities and dip from refraction survey data for dipping layer on a half-space. Find the reflection coefficient between two layers given velocities and densities. Will there be a polarity reversal? Find the velocity and depth to a single, horizontal layer using reflection times for different offsets. Given N geophones, and the array is moved n geophone spacing each time, what fold coverage will result? When N signals (and noise) are summed, how much is the signal amplitude increased? the noise? What is the improvement in the signal-noise ratio?

Copyright 2007, Judson L. Ahern