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By Andrea Snell Revised by GBrenneman
S and How they shape the Earth
Earthquakes are a sudden movement of Earth’s crust that releases energy.CA quake
▪ 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.
Types of stress in the Earth’s crust lead to fault lines.
Types of Faults
• Strike-slip faults
• Normal Faults
• Reverse Faults
Normal Faultsanimation of normal fault
Normal Faults create space. Two pieces of the crust pull apart, spreading the crust apart.
Reverse Faultsanimation of reverse fault
• 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 faultsanimation of strike-slip fault
• 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 Focusvideo 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 EarthDemo of S waves and P waves
Primary Waves, or P Wave, are “push-pull” waves that cause back-and- forth 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 slow- moving.
Surface WavesSurface 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
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
▪ Protect Yourself (interactive game)
▪ Animation of how to stay safe
Landforms created by Earth’s stresses Part Two
Mountain Building
▪ 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.
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
