Introduction Geophysics

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Grading Basis
The breakdown for the grading is as follows.

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Final project:

20%

Mid-term exam:

20%

Final exam:

40%

Quizzes:

20%

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Geophysics?
• Apply the principles of physics to the study of the Earth
• Investigation of the interior of the Earth involves taking measurements at or
near the Earth´s surface that are influenced by the internal distribution of
physical properties. The analysis of these measurements reveals information
on the Earth´s interior

This could be the
discovery of the century.
Depending, of course, on
how far down it goes…
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Geophysical measurements:
tool to obtain an image of the subsurface
• Mapping of geological structure
• Detect objects

Source Receiver
S


Measurement
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R

S

R

Processing

Image
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Aim of the course
• Complete overview on geophysical methods (potential, diffusive and
wave field methods)
• Understand the possibilities and limitations of geophysical techniques
• Understand the basis in qualitative and quantitative interpretation
of geophysical data
• Give general basis for more advanced studies

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Investigating the Near Surface

Often use a combination of
geophysical methods to remove
interpretation ambiguities

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Recommended textbooks:


Reynolds, J., 2011, An introduction to Applied and Environmental Geophysics, Wiley-Blackwell. ISBN:978-0-471-485360.



Rubin,Y. and Hubbard, S.S., 2005, Hydrogeophysics (Water Science and Technology Library), Springer, 523 pp, ISBN:
1402031017

Additional References:

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


Butler, D.B., Editor, 2007, Near Surface Geophysics, Investigations in Geophysics #13, Society of Exploration
Geophysicists, Tulsa, OK.



Reynolds, J. M., 1997, An Introduction to Applied and Environmental Geophysics, John Wiley & Sons.



Kelly, W.E. and Mares, S., 1993, Developments in water science 44: applied geophysics in hydrogeological and engineering
practice, Elsevier Science Publishers.



Meju, M.A., 1994, Geophysical data analysis: understanding inverse problem theory and practice. SEG Course Notes
Series, Volume 6 (S.N. Domenico, Editor), Society of Exploration Geophysicists.



Milson, J., 2003, Field Geophysics, Third Edition, The Geological Field Guide Series, John Wiley & Sons.



Sharma, P. V., 1997, Environmental & engineering geophysics, Cambridge University Press.



Sheriff, R. E., 1994, Encyclopedic dictionary of exploration geophysics, Third Edition,




Geophysical Reference Series 1, Society of Exploration Geophysicists.



Telford, W.M., Geldart, L.P. and Sheriff, R.E., 1990, Applied Geophysics, Second Edition, Cambridge University Press.



Vogelsang, D., 1995, Environmental geophysics: a practical guide, Springer-Verlag. Ward, S. H., 1990, Geotechnical and
environmental geophysics, Volumes I-III, Society of Exploration Geophysicists.
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Geophysical methods
Potential methods:
• Gravimetry methods
• Magnetic methods
• Electrical methods

Diffusive methods
• Electromagnetic methods

Wavefield methods
• Georadar
• Seismic methods

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Structure of a lecture
Each topic will cover:
1.
2.
3.
4.
5.

Physical properties of rocks/geology
Basic equations for the method
Survey strategies and interpretation
Summary of the method: case histories and examples
Conclusions

Exercises will strengthen the explanations

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What is geophysics?
• Physics of the solid Earth
• Exploration of the structure and dynamic of the solid
Earth using physical methods
• Non-expensive and non-invasive methods
• Geophysical information is less discrete than
information from boreholes (and less expensive…). But
does not dispense with the need for drilling! Geophysics
can often optimize drilling requirements

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What is geophysics?
Various scales...
• Global geophysics
103 to 106 m
• Exploration geophysics
103 to 106 m
• Environmental and engineering geophysics <102 m

Various sources...
• Natural field sources or artificially generated sources
• Natural field source methods are more simple to carry out
but give less resolved pictures than artifical source methods

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Why Study Geophysics?

Who hires geophysicists?
 Energy Companies $$$
 Mining Companies $$$
 Government Jobs
 Engineering Consultants
 Environmental Consultants
 Bottom line…geophysics is highly employable
 /> />
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Why is Geophysics Useful?

Some sweeping generalizations…
 Geology:
 Limited to the surface of the Earth
 Geologists must infer the 3rd dimension
 Boreholes are an exception, but are expensive and only give limited information (<13 km depth).

 Gives extremely detailed data about small areas.
 Provides information about the past.

 Geophysics
 Adds information about the 3rd dimension.
 Can truly “look into the Earth”
 Gives less detailed information about much larger areas.
 Results are often “non-unique”
 Usually cannot give information about the past
 Exceptions are radiometric dating and paleomagnetism.

 Can study non-tangible things…e.g. forces
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How Do Geophysicists “Look at” Rocks?
 Geologists mainly look at rocks visually
 Map rock occurrence
 Visually identify mineral content
 Optical microscopes

 SEM
 “Direct” approach.
 Geophysicists “look at” rocks differently
 Measure properties such as density, resistivity, magnetic properties, elastic

moduli, radioactivity, etc…
 Use these properties to infer rock type / composition
 “Indirect” approach, but offers information that is not possible to visually obtain.
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Geology vs. Geophysics
 At the end of the day geology and geophysics are both useful

when studying the Earth.

 Geophysics does not replace traditional geologic study; it

compliments it.

 The best geologists understand and appreciate geophysics
 The best geophysicists understand and appreciate geology

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Definition: model
A model is a simple and ideal view of a physical reality

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Operative physical properties
•
•
•
•
•
•
•
•

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Seismic: density and elastic moduli
Gravity: density
Magnetic: magnetic susceptibility and remanence
Electrical resistivity: electrical conductivity

Electrical induced polarization: electrical capacitance
Self potential: electrical conductivity
Electromagnetic: electrical conductivity and inductance
Radar (GPR): dielectric constant

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Definition: contrast
To characterize different material using geophysics, a contrast
must exist (i.e. a difference in the physical properties)

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Environmental/engineering geophysics
• Hydrogeology
• Exploration of waste sites and pollutant
• Exploration for bulk mineral deposits (sand and gravel)
• Ground stability, permafrost, glaciology
• Archaeology
• Cavity detection, cable location etc
• Subsurface geological imaging for civil engineering
• Bulk modulus and shear modulus for civil engineering

• Alternative energy sources

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Environmental Geophysics

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Engineering Geophysics

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Noise in geophysical data acquisition

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Gravity

micro-gravimetry
in urban environment

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Magnetic

magnetic surveys on landfills

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