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GEOG 140 Study Guide - Comprehensive Final Exam Guide -


Department
Geographical Sciences
Course Code
GEOG 140
Professor
Keith Yearwood
Study Guide
Final

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GEOG 140

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Earthquakes, Tsunamis, Volcanoes 3/7/2016 11:45:00 PM
EARTHQUAKES
What are earthquakes and what causes them to take place?
[Definition:] Earthquake: an earthquake is a trembling or shaking
movement of the Earths surface
Earthquakes that occur in the bottom of the sea are not considered natural
disasters
- What causes these movements?
Seismic Waves
o Underground waves
o These are waves that move through the earth(also the water)
Waves are created by movement
Movement of magma into the crust in volcanoes create seismic
waves
o This is how scientists are able to tell if a volcano is going to
become active
Huge man-made explosions cause movement too!
The tectonic plates are under tension and sometimes they move
suddenly
o This movement is accompanied by a sudden release of energy
This creates the seismic (underground) waves
o The point where the movement occurs is called the focus
The waves radiate from the focus in all directions
o The point above the focus on the earth’s surface is called the
epicenter
The waves are strongest nearest the epicenter
o The fault is the crack that separates the two sides of the
earth
- What are plate margins (or boundaries) and why are earthquakes
associated with them?
The earths crust is not one huge solid slab of rock
Rather the crust is made up of about 20 huge slabs of the earth
called tectonic plates (or crustal plates)
o Tectonic Plates = Crustal Plates
The plates are separated by huge cracks called faults
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o Notice some of these faults are found not only on the land but
also on the sea floor
o The movement of the earth’s crust takes place primarily along
these faults
o There are also minor faults throughout the earth’s crust as
well and movement along these also occur
The earthquake that took place recently in Virginia is an
example of this
The sections of the crust are held in great tension and stress
against each other
A sudden movement releases the stress and produces the energy
TSUNAMIS (Japanese for Harbor Wave)
Japanese word: Harbor Wave
A Tsunami is a wave train, or series of waves, generated in a body
of water by an impulsive disturbance that vertically displaces the
water column
Regular waves are caused by wind
When the ocean floor moves suddenly, the water becomes
displaced
Tsunamis travel over great distances at high speed (hundreds of
miles per hour)
In deep water they are not high waves (approximately 4 feet high)
They become very high and destructive as they approach shallow
water
The speed diminishes and the wave height grows because the wave
energy remains constant
Waves sometimes get as high as 100 feet and cause great damage
to the coast
Mechanics of a tsunami wave:
The waves slows down because the bottom of the wave drags along
the shallow seabed
The energy of the wave remains the same however
This causes the wave to grow in height as the energy that propelled
the wave is used to cause it to grow
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