APPLIED
GEOPHYSICS
AN INTRODUCTION
FRED BEEKMAN
JEANNOT TRAMPERT
COURSE OVERVIEW
Course content
Overview of the classical potential field and seismic methods. The course
will review the basic physical principles underlying the various exploration
techniques and will show how the field data are acquired and interpreted.
Aim
Understanding the fundamental concepts of geophysical exploration
techniques and being able to put these concepts into practice.
Exercises
Through paper exercises and computer practicals the students will solve a
range of realistic problems. Students will acquire an appreciation for which
techniques are appropriate for which application.
Grading
•30% exercises+practicals
•70% written exam
COURSE OVERVIEW
Literature
“Introduction to Applied Geophysics”
by Burger, Sheehan and Jones.
Norton, 2006.
“An introduction to Geophysical
Exploration” by Keary, Brooks
and Hill. Blackwell, 2002.
“An introduction to Applied and
Environmental Geophysics” by
Robinson. Wiley-Blackwell, 2011.
“Applied Geophysics” by
Telford, Geldart and Sheriff.
Cambridge UP, 1990.
APPLIED GEOPHYSICS
Geophysics is the application of physical principles and methods to
problems in Earth Sciences
There is no clear distinction between general and applied geophysics…
…but in general geophysics methods are typically applied to solve
academic questions, whereas applied geophysics can be characterized
by the application of geophysical methods for commercial purposes
(“making money”).
Examples:
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oil, gas, coal, minerals, …
groundwater
geo-engineering (tunnels, dams, …)
archeology
pollution
…
APPLIED GEOPHYSICS
Physical methods used in applied geophysics:
 Seismic methods: refraction and reflection seismics; VSP; seismic surveys
 Gravity surveying: density contrasts; anomalies; gravimeters; corrections
 Geomagnetic surveying: induced rock magnetism; anomalies
 Electromagnetic surveying: EM fields; survey methods; ground penetrating
radar (GPR)
 Electrical surveying: resistivity; VES soundings;
 Borehole petrophysics: well logging; core sampling;
 Radiometrical surveying: radioactive decay; isotopes; dating;
 Geothermal methods: heat flow; conduction;
APPLIED GEOPHYSICS
Passive versus Active methods
 Passive methods:
Use naturally present sources/fields to investigate properties of the subsurface
Examples:
 Gravity
 Earth’s magnetic field
 Earthquakes
 Active methods:
Use man-made source to image structure of subsurface
Examples:
 Dynamite, air guns, …
 EM waves
 Electrical currents
APPLIED GEOPHYSICS
To select the most appropriate geophysical method to investigate a
certain task/problem, following aspects need to be considered:
 What are the relevant physical properties? (porosity, pemeability, seismic
velocity, density, …)
What spatial scales are relevant?
 What are the field conditions? (e.g. urban, offshore, …)
 Which acquisition geometries are optimal? (e.g. 2D vs 3D seismics)
 Is there useful a priori information?
Is there a cheaper alternative?
The answer to these questions will depend strongly on the
particular task/problem
What is applied geophysics ?
Why
applied
geophysics ?
Applied geophysics infers property contrasts inside the
earth from surface (borehole) measurements
 Remote sensing
Be aware of biased data!
The data need to record
the true signal
Noise is also an issue
Be aware of a biased interpretation!
A physical theory calculates observables given appropriate
model parameters and theory  forward modelling
The inverse problem is often non-unique!
Several geophysical methods
should be used together
Interpretation requires
geological knowledge
How many dimensions?
How many dimensions?
How many dimensions?
CLASSIFICATION OF
GEOPHYSICAL METHODS
Seismic methods (active)
• Reflection seismics
• Refraction seismics
Potential field methods (passive)
• Gravity
• Geomagnetic
Electrical methods (active)
• Electrical resistivity
• Spontaneous (Self) Potential
• Induced Polarisation
CLASSIFICATION OF
GEOPHYSICAL METHODS
Electromagnetic methods (active)
• Many methods among which ground penetrating radar
Well logging (active and passive)
SEISMIC METHODS
MAINLY MEASURE TRAVEL TIMES
AND AMPLITUDES WHICH DEPEND
ON DENSITY AND ELASTIC MODULI
SEISMIC METHODS
MAINLY MEASURE TRAVEL TIMES
AND AMPLITUDES WHICH DEPEND
ON DENSITY AND ELASTIC MODULI
POTENTIAL FIELD METHODS
Gravity measures spatial variations of the gravitational field
due to lateral variations in density.
POTENTIAL FIELD METHODS
Geomagnetics measures spatial variations of the intensity of
the magnetic field due to lateral variations in magnetic
susceptibility.
ELECTRO MAGNETICS
GROUND
PENETRATING
RADAR
MEASURES TRAVEL
TIMES OF
REFLECTED RADAR
WAVES
VELOCITY IS
CONTROLLED BY
THE DIELECTRIC
CONSTANT