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GEOL
440: Geophysics (Spring 2005)
Solid
earth geophysics is introduced and put in the context of its role in
the establishment of our modern understanding of the dynamic Earth.
The course stresses general approaches of quantitative analysis when
linking surface observables with physical and structural models of
the inaccessible interior of our planet. Topics include kinematics of
plate tectonics, the magnetic and gravity field and their anomalies,
earthquakes, seismic wave propagation, reflection and refraction
seismics, geochronology, heat transport, mantle convection, and deep
Earth composition and dynamics. Includes required applied geophysics
field trip with seismic and gravity experiments (March 24 – 26,
2005)
Prerequisite:
MATH 126; co-requisite: PHYS 135bL or PHYS 152L; i.e. some
exposure to math (calculus and linear algebra) and physics is
helpful, but special permission may be obtained from instructor.
Instructor:
Prof. Thorsten Becker, ZHS269, 213-740-8365, twb
-at- usc.edu
Office
hours: Monday, 1pm, and by appointment
Course
Structure
Lectures:
Tue and Thu 9:30 - 11am; ZHS123
Lab:
to be arranged, 2 hours
Grading:
Homework: 40%, Discussion group participation 20%, Midterm (oral
exam) 10%, Field trip report: 30%:
Letter
grades: 90-100%: A, 80-90%: B, 70-80%: C, 60-70%: D, 50-60%: F.
Grades may be improved by good attitude and working on optional
assignments.
Late
policy for homework: Homework problems are due one week after
they are handed out. Up to one day late: 10% off your score; one to
two days late: 25% off your score; later than two days: zero score.
If you have special circumstances that keep you from working on the
homework, you may be granted an exception on a case to case basis.
Texts
Fowler,
C. M. R. The Solid Earth : An Introduction to Global Geophysics,
2nd edition, Cambridge University Press.
Additional
books on reserve at the Science & Engineering Library in order of
relevance for the course:
Mussett,
M; Khan, M. A.: Looking into the Earth : An Introduction to
Geological Geophysics. Cambridge University Press, 2000. (Nice
intro with focus on applied geophysics methods.)
Lowrie,
W. L.: Fundamentals of Geophysics, Cambridge University
Press, 1997. (Comprehensive geophysics intro book, a bit more
advanced and quantitative than Fowler.)
Turcotte,
D.; Schubert, G.: Geodynamics. 2nd ed., Cambridge
University Press, 2002. (Standard geodynamics textbook.)
Stacey,
Frank D.: Physics of the earth. 2nd ed., Wiley,
1977. (A classic, now a bit outdated. Nice quantitative treatment of
general geophysics problems.)
Schubert,
G., Turcotte, D., and Olson, P.: Mantle Convection in the Earth
and Planets, Cambridge University Press Press.
Syllabus
Week
1: The Earth and planets (01/09 – 01/13)
Introduction
to Geophysics, methods, applications. Celestial mechanics, Euler's
laws. Age of the Earth I. Origin of the solar system. Composition,
shape and character of the Earth and terrestrial planets.
Reading:
Web material on comparative planetology (linked from course web
page); Turcotte & Schubert, chap. 1; Schubert et al., chap.
14.
Lab:
Possible tectonic origin of features on Mars and Venus. Role of plate
tectonics on shaping the surface of planets. The role of water and
the biosphere for tectonics, and vice versa. The origin of the moon.
Week
2: Plate tectonics (01/16 – 01/20)
Types
and definition of plate boundaries. Continental vs. oceanic
plates. Kinematic description of plates on the surface of a sphere.
Present day plate motions from geology, seismicity and geodesy.
Behavior of triple junctions.
Reading:
Spherical trigonometry handout; Fowler p. 5 – 24; Continental
drift movies (linked on web site)
Lab:
Reconstruction of past continental locations and apparent polar
wander curves. Evaluating triple junction stability using geometric
methods.
Week
3: Earth's magnetic field (01/23 – 01/27)
Character
of the Earth's field. Electromagnetic fields and potentials. Core
convection and the dynamo. Magnetic substances, thermo-remanent
magnetization. Measurement and interpretation of frozen-in
magnetization for plate tectonics.
Reading:
Fowler p. 43 - 67, 373 – 381; Math hand out; Review articles on
the core dynamo (optional)
Lab:
The Rikitake dynamo: coupled rotating disks, the Lorentz force.
Using Matlab to solve coupled ordinary equations. Nonlinear dynamics:
bifurcations, mode switching, critical dependence on initial
conditions. What is chaos?
Week
4: Present and past plate motions (01/30 – 02/03)
Reconstruction
of plate motions. Global and regional tectonophysics. block
rotations. Super-continental break-up, rifting, the Wilson cycle.
Intra-plate deformation as seen from geodesy. Rock rheology, elastic
and viscous behavior on different timescales.
Reading:
Fowler p. 67 – 99.
Lab:
The Global Position System. Measuring relative travel times,
trigonometry to locate position, technical aspects of using GPS.
Accuracy and precision, resolving velocity and strain fields.
Week
5: Rocks and wave seismology (02/06 – 02/10)
Stress
and strain, elasticity, isotropic and anisotropic materials. The wave
equation, body and surface waves. Normal modes. Snell's law. Phases
and phase picking on seismograms. 1-D Earth models, PREM.
Reading:
Fowler, p. 101 – 110, 126 – 129; Plane wave handout;
Lab:
Solutions to the wave equation, vector and scalar potentials.
Harmonic solutions to the vibrating string problem. Spherical
harmonics.
Week
6: Earthquakes (02/13 – 02/17)
Elastic
rebound theory, the seismic cycle. Measures of earthquake size and
intensity. Energy, moment, magnitude. Gutenberg-Richter and Omori
laws. Types of faulting and beach balls. Global seismicity
distribution.
Reading:
Fowler, p. 110 – 125, 130 – 140; Optional homework 1: Regional
Harvard CMTs.
Lab:
Determining earthquake magnitude and location from regional
seismograms. Review for midterm.
Week
7: Midterm (oral) – Refraction seismics (02/27 – 03/03)
Refraction
seismics. Reflection, refraction, and transmission coefficients.
Elastic properties of crustal rocks.
Reading:
Fowler, p. 140 – 157.
Lab:
Refraction survey techniques: Interpretation of layered structure
signals, inclined layers, ondulations of strata. Methods of inducing
energy for seismic surveys.
Week
8: Reflection seismics I (03/06 – 03/10)
Reflection
seismic surveys. Sources and receiver technology.
Reading:
Fowler, p. 157 – 196. Matlab introduction handout. Mussett &
Khan, chap. 3
Lab:
Using Matlab to plot data. Fourier transforms, filtering of data.
Week
9: Gravity (03/20 – 03/24)
Newton's
law, gravity. Gravity potentials, acceleration. Shape of the Earth,
the geoid. Gravity anomalies.
Reading:
Fowler, p. 193 – 213; Gravity anomaly handout.
Lab:
Interpreting simple gravity anomalies, buried sphere, faults,
sheets. Free-air, Bouguer, and other corrections. Non-uniqueness of
inversions. Characteristic lengths, self-similar solutions.
Required
fieldtrip: March 24 – 26.
Excursion
to Death Valley to conduct refraction seismic survey on fault scarps
and measure gravity profiles to detect depth to basement of buried
normal faults.
Week
10: Processing and interpreting fieldtrip results (03/27 – 03/31)
Applying
gravity data corrections. Plotting results on a map and in profiles.
Interpreting gravity anomaly curves. Interpreting refraction survey
results.
Reading:
Musset & Khan: excerpts from chaps. 6 & 8.
Lab:
Using Matlab to fit data. Mean and standard deviation.
Least-squares with errors. Curve-fitting. Inverse theory, L-curves,
trade-off between misfit and model complexity.
Week
11: Reflection seismics II and EM methods (04/03 – 04/07)
Interpretation
of seismic sections. Analogy of reflection seismology with
electro-magnetic prospective methods, georadar. Electrical
resistivity surveys.
Reading:
Fowler, p. 157 – 196. Matlab introduction handout. Mussett &
Khan, chap. 3
Lab:
Using Matlab to plot data. Fourier transforms, filtering of data.
Week
12: Heat I: transport and budgets (04/10 – 04/14)
Heat
transport by conduction and convection. Geotherms. Half-space cooling
and oceanic bathymetry. Global heat flow maps. Continental and
oceanic heat budgets.
Reading:
Fowler, p. 269 – 303. Finite difference method handout.
Lab:
Solving the diffusion equation with finite differences using Matlab.
Stability and accuracies of numerical schemes. Diffusion timescales.
Week
13: Heat II: Convective transfer (04/17 – 04/21)
Thermal
convection, Rayleigh number. Thermal boundary layers. Thermal
structure of the Earth. Mantle convection simulations.
Reading:
Fowler, p. 353 – 370, 303 – 324.
Lab:
Using Virtual Earth (CU Boulder) online mantle convection
simulations to understand the role of the Rayleigh number on the
style of convection. Discuss movies of convection for temperature and
stress dependent viscosities.
Week
14: Whole Earth structure from Geophysics (04/24 – 04/28)
Mechanical
constraints: post-glacial rebound and geoid constraints on the
viscosity of the mantle. Oceanic lithosphere: ridges, transforms and
subduction zones. Continental lithosphere: collision and rifts.
Seismic tomography. Deep Earth structure.
Reading:
Fowler, p. 214 – 230, 326 – 353.
Lab:
Using the Adams-Williamson equation to infer a 1-D density and
temperature model. Variations from a 1-D Earth model, plates, plumes,
and slabs. Resolution of seismic tomography.
Reports
on Field Trip are due May 5, 2005.
Disability
notice
Students requesting
academic accommodations based on a disability are required to
register with Disability Services and Programs (DSP) each semester. A
letter of verification for approved accommodations can be obtained
from DSP when adequate documentation is filed. Please be sure the
letter is delivered to us (or to your TA) as early in the semester as
possible. DSP is open Monday-Friday, 8:30-5:00. The office is in
Student Union 301 and the phone number is (213) 740-0776.
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