Chapter 5 Fast Changes on Earth
Lesson 2 - Earthquakes
Main Idea
Earth’s outer layer, the crust, is made up of large slabs of rock called plates. The sudden
movement of the plates can cause changes to occur to the Earth’s surface.
Vocabulary
Crust (248) – Earth’s outer most layer
Plates (248) – gigantic slabs of rock making up the crust
Fault (249) – where the plates come together
Earthquake (249) – movement in the Earth’s crust that are caused by a sudden shift in the
Earth’s plates
Tsunami (252) – giant waves caused by earthquakes on the ocean floor
What are earthquakes?
Main Idea
Earth’s crust is made up of plates.
Supporting Details
1. Fast changes take place on the crust, Earth’s outer most layer.
2. Earth’s moving crust
a. Crust is the thinnest layer of the Earth
b. Crust is made up of gigantic plates of rock called plates
c. The plates are like puzzle pieces making up the Earth’s surface
d. The plates are constantly moving
e. Faults are cracks and breaks in the Earth’s surface where plates come together
f. Earthquakes are caused by a sudden shift in the plates.
3. Where earthquakes happen
a. Earthquakes can happen near the edges of the plates
b. Many earthquakes happen along the ring of fire in the Pacific Ocean where some
of the plates meet.
What causes an earthquake?
Main Idea
Earthquakes occur when there is a sudden movement in the plates
Supporting Details
1. Earthquakes happen where the plates meet
2. Often times, the plates creep slowly moving only a few centimeters a year
3. Sometime, the movement is sudden
a. Energy released from a sudden movement of the plate shakes the crust
b. Can set a large earthquake in motion
4. Three types of faults
a. Normal fault
i. Plates pull apart
ii. Rocks above the fault surface move down
iii. Sierra Nevada mountains were formed this way
b. Reverse fault
i. Plate push together
ii. Rocks above the fault move upward
iii. Himalaya formed this way
c. Strike – slip fault
i. Rocks slide past each other in different directions
ii. San Andreas fault is an example of this type
5. Earthquake’s Vibration
a. During an earthquake, the ground may vibrate or shake
b. It may seem to roll
c. Sometimes the ground will split open
d. Vibrations of an earthquake are strongest where the earthquake first begins
e. Vibrations move through the crust in all directions similar to the water ripples
when a pebble hits the surface
f. As the vibrations travel away from the center, they weaken
What is a tsunami?
Main Idea
A tsunami is a giant wave caused by an earthquake on the ocean floor.
Supporting Detail
1. A tsunami is a giant ocean wave
a. Usually caused by an earthquake on the ocean floor
b. some caused by underwater landslides or volcanoes
2. The force of the earthquake causes a large wave to form
3. As the wave moves closer to shore
a. It drags along the ocean floor which slows the wave down
b. Soon the wave gets higher
4. Effects of a tsunami
a. Tsunamis may be a huge wall of water or a series of smaller waves
b. Tsunamis can travel at great speeds (960 km / hr or 600 mph)
c. Tsunamis can travel great distances
d. Tsunamis wash away the shore line and damage property along the shore
What are some safety tips for earthquakes and tsunamis?
Main Idea
You can protect yourself from earthquakes and tsunamis by being prepared.
Supporting Details
1. Earthquake safety
a. Place large, heavy, or breakable objects on lower shelves. Bolt down heavy
appliances
b. Locate safe spots in your house. This may be under a sturdy table or against an
inside wall
c. Hold family earthquake drills. Find a safe place to drop and cover and hold on.
Stay away from glass or things that can fall on you. Establish a family meeting
place.
d. If outside, move quickly to an open space. Avoid buildings, power lines, trees, or
anything that can fall on you.
e. If in a car, stop driving, stay in the car. Never stop under a tree or bridge.
f. If under debris, don’t move or kick. Cover your mouth.
2. Tsunami safety
a. If near the coast during an earthquake, listen to local news for possible tsunamis
b. If there is a tsunami warning, move to higher ground. Do not stay to gather
things.