S and How they shape the
Earth
By Andrea Snell
Revised by GBrenneman
Earthquakes are a sudden movement of Earth’s crust that
releases energy.
CA quake (clip)
Text pgs. 54-58
▪ The crust of the Earth is constantly moving, but are usually slow –
until a major earthquake takes place.
▪ About 95% of all earthquakes occur at or near the edge of moving
plates. Worldwide Earthquake Locator
▪ They occur along cracks in the Earth’s crust called faults. Faults are
associated with, or form, the boundaries between Earth’s tectonic
plates.
▪ Earthquakes do not occur randomly.
How do earthquakes work ?
Types of stress in the Earth’s crust lead to fault
lines.
Types of Faults
• Strike-slip faults
• Normal Faults
• Reverse Faults
Modeling Fault Types
Animations of fault types
▪ Foam Fault Models and Examples
Normal Faults
Normal Faults create space. Two pieces of the crust
pull apart, spreading the crust apart.
Reverse Faults
• Reverse faults squeeze the crust and push two blocks of crust on
top of one another.
Usually these faults are found in the Rocky Mountains and
Himalayas and cause mountains to form.
Strike-slip faults
• Indicates rocks are sliding past each other, with little to no
vertical movement. Both the San Andreas and Anatolian
Faults are strike-slip.
Epicenter and Focus (text pgs. 64-77)
video lecture
• The epicenter is the point the Earth’s surface, or land,
directly above the earthquake focus.
• The focus is the hypocenter of an earthquake. The
vibrating waves travel away from the focus of the
earthquake and move in all directions.
• Earthquakes do not start at the epicenter.
Earthquake Waves
• The energy from an earthquake travels away
from the focus in waves.
• The waves travel in different speeds.
• There are two types of waves
1. Those that travel inside the Earth
2. Those that travel only at the surface
Waves that travel inside the Earth
Demo of S waves and P waves
Primary Waves, or P Wave, are “push-pull” waves that cause back-andforth vibrations in the same direction as the waves
move. The P-Waves are fast-moving.
Secondary Waves, or S waves, cause vibrations at right angles to the
waves direction of travel. The S waves are slowmoving.
Surface Waves
Surface waves explanation
• Surface waves- only travel only at the surface and move slower
than P-waves or S-waves.
• These waves make the ground roll and sway. They can cause a
great deal of damage to buildings, roads, and other surface
features. pool shakes
Locating an Earthquake Lab
Preview for epicenter lab (see teacher for lab sheet and tools)
Measuring Earthquakes
Earthquakes are recorded by instruments called seismographs. Seismographs record
seismic waves. The motion is measured electronically and recorded in a computer. They
can measure both S and P waves. The size of the waves is called magnitude.
To tell the strength of the earthquake scientists use a Richter Scale. The larger the
number on the Richter Scale, the larger the earthquake. You won’t even feel an
earthquake if it is below a 3. Today scientists also use the Moment-Magnitude scale.
NASA sci file
Each number is 32 times greater than the previous number.
• 4.0 -Would shake your house like a large truck passes by.
• 5.0 – Things might fall off shelves. Walls might crack and windows break.
• 7.0 – Weaker buildings could collapse. Also cracks may occur in streets.
• 8.0 – Buildings and bridges could fall down and large cracks in surface.
• 9.0 and up- Large scale damage and cities flattened.
Testing Buildings for Earthquake-Proofing
▪ Testing
Japan’s Mega Earthquake
Japan's Mega Earthquake (48 mins.)
Tsunamis can be caused by earthquakes
▪ Japan's tsunami and how it happened (documentary)
How to Protect Yourself during an Earthquake
Text pg. 77
▪ Protect Yourself (interactive game)
▪ Animation of how to stay safe
Landforms created by Earth’s stresses
Part Two (text pgs. 58-61)
Mountain Building
Demonstration
▪ mountain building (clip)
Fault-Block Mountains: When normal faults uplift a block of rock, a fault-block mountain forms. The
Grand Tetons in Wyoming and Idaho are one such example. Mountain Building Types (clip)
More mountains
Folds are compressions from two plates colliding. The Appalachian Mountains were
formed in this way.
Anticlines and Synclines
Anticlines and Synclines can be found in folded mountains. Anticlines, such as the Black
Hills in South Dakota, are the folds in the rock that bend upward while synclines, such as
the Illinois Basin, are the folds in the rock that bend downward.
Plateau - a large area of flat land elevated high above sea level
How the Grand Canyon Was Formed
Science is so Cool!
▪ earthquake exhibit
▪ Hands-ON Fun
▪ Make It Quakeproof (add link)