GEOL 414 Applied Geophysics

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GEOL 414 Applied Geophysics

• Fall Semester 2006
• Principles of various geophysical methods and
  their application to geologic problems.
  Prerequisites Geology 101, Mathematics 213,
  Physics 204 or 206. 3 credits.

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Applied Geophysics
Textbook Burger, Sheehan, and Jones,
Introduction to Applied Geophysics, 2006, W.W.
Norton Co. Inc., ISBN 0393-92637-0 Course
Goals To give students an understanding of the
physical principles of geophysical methods so
that they will appreciate the strengths and
limitations of the methods. After certain
fundamentals have been mastered, the students
study the procedures used in data acquisition and
use the department's equipment to conduct
geophysical surveys. The final phase of each
section of the course gives students training in
interpretation of geophysical data.
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Geol 414 Topic Sequence

• Section 1 Introduction to Geophysics -Methods,
  Units, Applications, Geophysical Societies,
  Geophysical literature
• Section 2 Gravity fundamentals
• Gravity surveying
• Gravity data reduction and analysis
• Section 3 Magnetic fundamentals
• Magnetic surveying
• Magnetic data reduction and analysis
• Section 4 Combined gravity and magnetic survey
  field project
• Section 5 Electrical Methods and Surveying
• Section 6 Seismology fundamentals
• Section 7 Refraction seismology
• Section 8 Reflection seismology
• Section 9 Thermal methods

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American Geological Institute IndexGeology
Disciplines

• Geology
• Economic Geology
• Geochemistry
• Geophysics
• Paleontology
• Hydrology
• Soil Science
• Engineering Geology
• Oceanography
• Planetology

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American Geological Institute IndexSub-discipline
s in Geophysics

• General Geophysics
• Experimental Geophysics
• Exploration Geophysics
• Geodesy
• Geomagnetism paleomagnetism
• Gravity
• Heat Flow
• Seismology
• Marine Geophysics

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American Geological Institute IndexSub-discipline
s in Geophysics

• Extraterrestrial Geophysics
• Soil Physics
• Mathematical Geology
• Mineral Physics
• Stable Isotopes

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American Geophysical Union Sections

• Atmospheric Sciences
• Biogeosciences
• Geodesy
• Geomagnetism and Paleomagnetism
• Hydrology
• Ocean Sciences
• Planetary Sciences
• Seismology
• Space Physics and Aeronomy
• Tectonophysics
• Volcanology, Geochemistry, and Petrology

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Topics in some Geophysics Textbooks Applied
GeophysicsTelford, Geldart, Sheriff

• Gravity Methods
• Magnetic Methods
• Seismic Methods
• Electrical Properties of Rocks and Minerals
• Natural Electrical Sources
• Electromagnetic Methods
• Resistivity Method
• Induced Polarization
• Radioactivity Method
• Geophysical Well Logging

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Applied and Environmental GeophysicsReynolds

• Potential Field Methods
• Applied Seismology
• Electrical Methods
• Electromagnetic Methods

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Gravity

• Units - gals 1 gal 1 cm s-2
• Absolute gravity
• Relative gravity
• Range 983164 to 978049 mgals
• Property of Earth density distribution
• F Gmm r-2
• g Gm r-2

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Heat Flow

• Units mW m-2
• Q ??
• Q Q0 Ab
• A A0 e-z/b
• Range 103 to 0
• Mean 84 mW m-2

Laplaces equation
Poissons equation
The diffusion equation
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Magnetics

• Units nanoTeslas nT
• 7 measurable components
• Declination
• Inclination
• F (total field)
• X (north)
• Y (east)
• Z (vertical)
• H (horizontal)

Coulombs Law
Field Strength
Magnetic Intensity
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Magnetics

• Units nanoTeslas nT
• Main field 60,000 to 30,000 nT
• Core dynamo
• External field 10s nT
• Diurnal, seasonal, ionization of atmosphere
  solar wind currents, storms
• Anomalous field 1000s nT
• Magnetic susceptibility of crust

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Seismology

• Measured units time distance
• Interpreted units velocity
• Application interpretation rock type, structure
• Refraction
• Reflection
• Earthquakes

The Wave Equation
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Resistivity

• Units ohm m
• V iR
• R rA/L
• Various arrays with characteristic electrode
  spacing

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Bouguer Gravity of the Lake St. Martin Impact
Structure
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Residual Gravity of the Lake St. Martin Impact
Structure
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Surprise Valley, California
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Surprise Valley, California
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Surprise Valley, California Digital elevation
model
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Surprise Valley, California Bouguer Gravity
contours Red lines are seismic lines Black lines
are gravity profiles seen in next two slides
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Surprise Valley, California
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Surprise Valley, California
Surprise Valley, California Bouguer gravity
profiles
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Surprise Valley, California Vertical derivative
of the Bouguer gravity profiles
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The Geoid
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Gravity at UND

• The predicted gravity is given in units of
  'milligals' 1 gal 1 cm sec-2 1 kilogal
  1000 gal 1 milligal 1/1000 gal Latitude
  47.91877432
• Longitude 97.06790622
• MSL Height 252.9
• Predicted gravity 980798 /- 2 milligals