Geophysics

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Applied geophysics – Introduction
Techniques and targets
Introduction to geophysical methods:
Reference:
Sharma p1-10
Reynolds p1-27
Applied geophysics – Introduction
What do we mean by applied geophysics?
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Applied geophysics – Introduction
Remote sensing
Constraining the Earth’s sub-surface with observations at the surface
Geophysical techniques measure physical phenomena:
• Gravity
• Magnetism
• Elastic waves
• Electricity
• Electromagnetic waves
Which are sensitive to sub-surface physical properties:
• Density
• Magnetic susceptibility
• Seismic wave velocity and density
• Resistivity
• Conductance/inductance/permitivity
Oh, and it’s relatively cheap
Applied geophysics – Introduction
Active and passive
Active
Transmit a signal into the subsurface and record what comes back
• Seismic arrival – explosions
• Electrical current
• Electromagnetic waves
Passive
Measure naturally occurring phenomena
• Gravity field
• Magnetic field
• Seismic arrivals - earthquakes think scale
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Applied geophysics – Introduction
Our scale …meters to kilometers
The techniques we’ll talk about are used in the fields of
• Environmental geophysics
• Engineering geophysics
• Exploration geophysics
Applied geophysics – Introduction
Planning a survey
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Applied geophysics – Introduction
Target identification
Applied geophysics – Introduction
Magnetics
Examples
Main use: locating steel drums and pipes
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Applied geophysics – Introduction
Examples
Seismic reflection
Applied geophysics – Introduction
Seismic reflection
Examples
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Applied geophysics – Introduction
Ground penetrating radar
Examples
Applied geophysics – Introduction
Ground penetrating radar
Examples
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Applied geophysics – Introduction
Techniques and targets
Magneto-telluric Resistivity s P P m m
EM – Ground penetrating Permitivity, conductivity m P P P s P P P radar EM - VLF Conductance, inductance m m P m s s s m m
Electromagnetic (EM) Conductance,