9/11/2012 7:40:00 AM
Earthquake shaking/vibration of ground rocks undergo deformation and
break suddenly along a fault. (rocks break in a brittle fashion and then get
offset.)
Earth’s surface made of tectonic plates, which are always in constant
morning. (egg – crust of earth, shell of egg) made of cold material and
breaks brittly. (dropped egg, cracks (plate) boundaries between pieces
which are tectonic plates, they are mobile).
Plate tectonics Constant movement of the plates
Divergent
Convergent
Transform
Question: The most powerful and destructive earthquakes occur:
A. along divergent plate boundaries
B. along convergent plate boundaries (subduction zones)
Divergent margins
Magma is injected into crack (boundary between two plates), plates are
forced apart, cools and becomes new crust. Spreading rate, 1 – 15 cm per
year.
Example: Atlantic ocean is a divergent margin, being torn, the two plates are
separating continuously at a rate of several cm/y.
Example 2: Red sea, like the atlantic ocean except its younger, started to
spread apart much more recently. Arabian plate, volcanism is evident as a
result of rifting. Middle of red sea in submarine, hydrothermal springs,
magma being erupted by volcanoes, along that specific margin of Red Sea.
Convergent margins (subduction zones)
Instead of two plates moving apart, when you have two plates coming
together, the friction with the plates rubbing off each other, earthquakes are
very large and frequent. Oceanic plate dives/slides beneath continental
plate, recycling material back into mantle of earth process known as
subduction. Subduction environments large earthquakes. Older denser goes down, younger less denser above.
Convergent margins II
If two continental plates collide, do not subduct they are too buoyant.
Intense compression with crustal shortening and thickening occur, large
destructive earthquakes also are generated in this situation. (crust becomes
thick).
Example: Alps in Europe/Himalayas
Thickness of continental crust in Himalayas: 5 km
Normal oceanic crust from sea floor to mantle, is normally 5 km - thinnest
Thickness – 100 km
India has been driving north into the rest of Asia, by creating the Himalayas.
Transform margins/Transform plate boundary
The third type of plate margin is called a transform boundary.
Chile/Alaska/Indonesia/Japan potential good papers.
Pacific Rim of Fire
This notorious zone is characterized by SUBDUCTION ZONES
Earthquakes here are violent
Friction from subduction produces large destructive earthquakes.
Faults associated with earthquakes
Linear planes of weakness along earth, when rocks break fast, earthquake
happens.
Three types of dominantly vertical faults
Normal fault: Generated in an area where things are being torn apart
(divergent), it is the result of tensional forces/rifting. Pulling rock apart.
Reverse and thrust faults are the result of: horizontal compression.
Faults whose movement is dominantly horizontal
These faults are termed strike slip faults
Use upper block to evaluate if moving left or right relative to the lower block
They are a small scale version of transform tec
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