Geoph 325

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Geoph 325

• Gravity, Magnetic and Electrical Techniques
• Instructor Mathieu Dumberry

(Special thanks to Martyn Unsworth)
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• A1 What is Geophysics?
• The study of the Earth using the basic principles
  of physics.
• Once pursued as an individual discipline, but now
  realized that geophysics is most effective when
  seen as integral part of the Earth Sciences
• Interpretation of geophysical data requires input
  from other branches of Earth science such as
  structural geology, geochemistry, fluid
  mechanics, etc. (and vice versa)

Geodynamics
Exploration geophysics
How we find out what is inside the Earth?
How does the Earth work?
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(No Transcript)
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A2.1 Radial structure of the Earth
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Depth 5 km Temperature 50 C Layer
Crust Rock Sedimentary Oil and gas
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Depth 30 km Temperature 300 C Layer
Crust Rock Granite
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Depth 100 km Temperature 500 C Layer Upper
mantle Rock Silicate minerals Olivine, spinel
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Depth 1000 km Temperature 2000 C Layer
Lower mantle Rock Silicate minerals Perovskit
e
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Depth 3000 km Temperature 4000 C Layer
Outer core Rock Liquid iron
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Depth 5000 km Temperature 5000 C Layer
Inner core Rock Solid iron
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Depth 6371 km Temperature 6000 C Layer
Inner core Rock Solid iron
Vancouver to East coast
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A2.2 Surface structure of the Earth
North American Plate
Eurasian Plate
African Plate
Pacific Plate
South American Plate
Indo-Australian Plate
Antarctic Plate
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Plate Boundaries

• 1) Convergent (destructive) boundaries

a) Ocean-Ocean (e.g. Tonga trench)
b) Ocean-Continent (e.g. Andes)
http//pubs.usgs.gov/gip/dynamic/dynamic.html
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Plate Boundaries

• 1) Convergent (destructive) boundaries

c) Continent-Continent (e.g. Himalayas)
http//pubs.usgs.gov/gip/dynamic/dynamic.html
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Plate Boundaries

• 2) Divergent (constructive) boundaries

a) Mid-ocean ridges (e.g. mid-atlantic)
b) Continental rifting (e.g. Afar)
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Plate Tectonics
A synthesis of ideas leading to an understanding
of the dynamic nature of the planet that explains
a wide variety of geological and geophysical
observations.
http//pubs.usgs.gov/gip/dynamic/dynamic.html
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A2.2 Surface structure of the Earth
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A2.2 Surface structure of the Earth
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A2.2 Surface structure of the Earth
Chi-Chi earthquake, Taiwan, 1999
San Andreas Fault, 1906
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A2.2 Surface structure of the Earth
Rupture of 1999 Izmit and Duzce earthquakes,
Western Turkey
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A3 Overview of exploration methods
Active/passive methods
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A3 Overview of exploration methods
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Local Gravity anomalies
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Global Gravity anomalies
mgal
(Lmax 10)
(Lmax 200)
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Electrical resistivity methods
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Local magnetic exploration methods
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Global Magnetic field at the surface
Vertical component between 1590-1990
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Magnetic field at the CMB
Vertical component between 1590-1990