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GEOL 106 Lecture Notes - San Andreas Fault, Silly Putty, Plate Tectonics

Geological Sciences and Geological Engineering
Course Code
GEOL 106
John Hanes

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GEOL 106 March 1, 2013
Transform fault margins under water, in the Mid-Atlantic Ridge
Right angle cracks
o Like ripping news paper
Two plates are sliding against each other an rubbing
o In between the two plates = transform margin
o Ex. San Andreas fault
Plate tectonics will not stop anytime soon
Where do earthquakes occur?
99% occur at plate margins
1% of earthquakes occur not at plate margins: intraplate earthquakes,
most are along former plate margins
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o Rivers are often faults ex. St. Lawrence, Ottawa, and Mississippi
Epicentres of earthquakes are down the river
The rivers used to be plate margins because during
Pangea, a bunch of cracks opened up in 3s, forming rivers
Failed arm: one of the 3 cracks that failed to open up
Still potentially prone to earthquakes
o 20,000 years ago there were ice sheets covering continents, ex.
Canada, which caused stress
o 12,000 years ago, the ice sheets were lifted up, causing
readjustment and potential cracks
o Knowing plate boundaries is important for Seismic risk
90% at depths less than 100 km
o Constructive margin
o Collision of plates in the Subduction zone
o On transform faults
10% at depths between 100 and 700 km
o Subduction zones from the destructive margins
Destructive margins are most dangerous because they
cause reverse dip slip faults
Earthquakes cannot occur in the asthenosphere because it is plastic
Lithosphere can continue until 700 km in the cracks created by the
destructive margins
- End of Seismic Risk-
Volcanic Risk
o Rocks formed when liquid (magma) cools and “crystallizes”, forming
mineralized grains, turning into ropy lava
Volcano: a place where magma comes to surface
Magma (liquid “rock)
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