** DRAFT SYLLABUS**
Electromagnetic Methods in Geophysics
This course could be taught in the Spring quarter under SIO239 Special
Topics in Geophysics, if there is sufficient interest.
Introduction and History.
- Motivation:
- Conductivity varies over a vast range, can use controlled sources,
depth resolution from centimeters to CMB, correlated with rock properties
-
- History:
- Foundations in physics (Ampere, Farady, Maxwell)
- Telluric and resistivity methods (Schlumberger)
- Global induction (Banks, Price)
- The MT method (Cagniard, Tikhonov)
- Controlled source EM (Ward, Stefanescu)
-
- Physics Refresher:
- Ohmic conduction
- Moving charges and magnetic fields
- Induction
Conduction in Rocks.
- Moving a charge:
- Free electrons (native metals)
- Semiconduction (sulphide ores)
- Electrolytic conduction (water, melt)
- Point defects in solids (silicate minerals), diffusion, Nerst-Einstein
equation
-
- Binary mixing laws:
- Role of geometry, tubes, films, pores
- Hashin-Shtrikman bounds
- Archie's 'Law'
-
- Surface properties:
- Clays, ion exchange capacity, streaming potential
-
- Polarization:
- What happens when a charge meets a boundary
-
- Anisotropy:
- Dependence of conductivity on direction
- Importance of scale
- - crystallographic anisotropy, textural anisotropy, structural anisotropy
Measuring Conductivity.
- Laboratory studies:
- Experimental setup
- Controlling polarization through AC current
- Cole-Cole diagrams and impedance spectroscopy
- Controlling the chemical environment
-
- DC resistivity (Earth as a resistor):
- Field practice and equipment
- Half-space theory
- 1D theory and digital Hankel transforms
- S and T equivalence
- Elementary inverse techniques
- - parameterized LS, regularized solutions, exact LS and the Bilayer
solution
-
- Self potential (Earth as a battery)
-
- Induced polarization (Earth as a capacitor)
-
- Magnetotelluric methods (Earth as an inductor):
- Geomagnetic spectrum from 10^-15 to 10^6 Hz
- Field practice and equipment
- Half-space theory and the skin depth
- 1D theory, inversion, D+ solution
- 2D and 3D solutions, finite elements and differences
- Response function estimation
-
- Geomagnetic methods:
- Banks and the P_1^0 approximation
- Global sounding using observatory data
- Local arrays, Parkinson vectors, spatial gradient method
- The 'coast' effect
- Satellites
-
- Controlled source methods:
- The many ways of coupling
- Basic theory
- Time versus frequency domain
- Equipment and field practice
- Borehole logging
-
- Radar:
- When the displacement current is used
- Conductivity and permittivity
- Propagation, attenuation
-
- Journey to the Center of the Earth
-
- Conductivity of crustal rocks:
- Importance of water, water conductivity versus P, T, salinity
- Role of conductive minerals, graphite, magnetite, illmenite
- Melt in volcanic systems
-
- The upper mantle:
- Importance of olivine
- Olivine conductivity versus P, T, Fe, O2
- High pressure phases of olivine
- Other minerals
-
- The lower mantle:
- Perovskite conductivity
-
- The core
Special to SIO- Working in the Marine Environment
- Seawater conductivity, attenuation of the geomagnetic spectrum
- Wet side of the coast effect
- Lorentz force and barotropic flow
- Equipment
- MT in the ocean
- Controlled source in the ocean
- The marine conductivity profile