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Lecture 6

EOSC 114 Lecture Notes - Lecture 6: Elastic-Rebound Theory, Beno Gutenberg, Linear Elasticity

Department
Earth and Ocean Sciences
Course Code
EOSC 114
Professor
Brett Gilley
Lecture
6

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Seismology, Earthquake Magnitude/Intensity
What is an earthquake?
- 1. A fault…
- 2. Elastic deformation
- 3. Brittle failure
Elastic rebound → How faults store and release energy.
Earthquakes: elastic rebound after cool, brittle rocks break
The waves produced by elastic rebound after cool, brittle rocks break in the
lithosphere (mostly in the upper lithosphere or crust)
Usually caused by forces from plate tectonic movement/motion
Learning Goals
- Describe what an earthquake is:
- what happens within the lithosphere?
- what do we feel at the surface?
- Understand concepts of
- stress causing strain
- elastic vs plastic vs brittle deformation
- Describe the motion and speed that different types of elastic waves travel through the
earth or over its surface:
- Body waves (compression (p) and shear (s))
- Surface waves (Rayleigh and Love)
- Explain why shear waves cannot propagate through fluids while compressional waves
can
Earthquakes:
- The waves produced by elastic rebound
- after cool, brittle rocks break in the lithosphere (mostly in upper lith. or crust)
- usually caused by forces from plate tectonic motion
- Brittle crust ruptures at hypocentre.
- Elastically deformed crust rebounds and vibrates, waves propagate away in all directions
Earthquake Magnitude: a quantitative measure of the “size” of an earthquake
Earthquake magnitudes define the amount of shaking or ground motion
the amount of ground motion is related to the amount of energy released.
Magnitude (energy released) affects everything else abt earthquake hazards
As magnitude increases, the earthquake:
shakes longer
damage more building
Earthquake Magnitude Scales…
Local (Richter) Magnitude (M(v)L)
Charles Richter and Beno Gutenberg (1935)
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