EPSC 185 Lecture Notes - Lecture 7: Epicenter, Elastic-Rebound Theory, Plate Tectonics
23 Jun 2018
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Plate tectonics
-In the beginning of the 20th century a controversial hypothesis was proposed by Alfred
Wegener. He proposed that continents were not fixed masses of land on the earth’s surface, but
rather moving continents on a Molten earth’s interior.
-His reasoning was actually quite simple at first - the continents of south america and Africa fit
together like a puzzle
-At first there must have been one large continent - Wegener named it Pangaea
-The edges of certain continents overlap- Wegener
-He was first to propose that all continents are moving. The continents began as one mass
theory.
-The mountain ranges on edges of two continents have the same composition so maybe they
were at one point all together. The Foggia.
-Mountain rangers on either side of the atlantic are the same - which brings us to the conclusion
that the land masses were once together as one.
-The mountain ranges were once beneath the Atlantic.
-Similar or identical fossils are found on both sides of the Atlantic
-If we remove the oceans, the first things we see are mountain ranges.
-In Iceland you can see the magma and mountain ranges forming at the surface and the magma
coming up is pushing two plates.
Plate tectonics: divergent, convergent, transform
Types of stress:
Compressional
a) non rotational
b) rotational (shear)
Tensional
Three types of dominantly vertical faults:
-A normal fault is the result of tensional forces (e.g. rifting)
-Reverse and thirst faults are the result of horizontal compression
-Dip-slip faults - a reverse fault occurs primarily across lithological units whereas a
thrust usually occurs within or at a low angle to lithological units
-Strike-slip faults - vertical dip, can not define hanging wall or footwall
Elastic rebound theory:
-The elastic rebound theory is an explanation for how energy is released during earthquakes
-As rocks on opposite sides of a fault are subjected to force, they accumulate energy and slowly
deform until their internal strength is exceeded
-At that time, a sudden movement occurs along the fault, releasing the accumulated energy, and
the rocks snap back to their original undeformed shape
-The deeper the rock in question, the more ductile it is
—> Warmer
-Rock that is deep enough to undergo plastic deformation will not generate earthquakes
-What is an earthquake?
—> An earthquake is the result of a sudden release of energy in the earth’s crust that
creates seismic waves
-Why are earthquakes so violent under compressive forces?
—> Killer earthquakes are located on the pacific
—> Mid oceans are kinder
—> Under compression the rocks are very strong
—> The higher the elastic limit is the more energy we store into the rock, so whenever we
reach the elastic limit the rock will snap loose which causes the killer earthquake
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
In the beginning of the 20th century a controversial hypothesis was proposed by alfred. He proposed that continents were not xed masses of land on the earth"s surface, but rather moving continents on a molten earth"s interior. His reasoning was actually quite simple at rst - the continents of south america and africa t together like a puzzle. At rst there must have been one large continent - wegener named it pangaea. He was rst to propose that all continents are moving. The mountain ranges on edges of two continents have the same composition so maybe they were at one point all together. Mountain rangers on either side of the atlantic are the same - which brings us to the conclusion that the land masses were once together as one. The mountain ranges were once beneath the atlantic. Similar or identical fossils are found on both sides of the atlantic.
