# Earth’s Crust in Motion

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Earth’s Crust in Motion
Chapter 5.1

What is an earthquake? What causes earthquakes? Earthquake: The shaking and trembling that comes from the movement of rock beneath Earth’s surface. When the tectonic plates of Earth’s lithosphere move they cause stress on the crust.

The more energy built up, the bigger the quake.
What is stress? How does it Create earthquakes? Stress: A force that acts on rock to change its shape or volume. Stress adds energy to the rock. Stress builds up until there is enough energy to overcome the friction, and the land shifts. The more energy built up, the bigger the quake.

What is Friction Friction is the force that opposes the motion of one surface as it moves across another surface. Friction exists because surfaces are not perfectly smooth. Rocks move along a fault depending on how much friction there is between opposite sides of the fault. How_Does_Plate_Movement_Generate_Earthquakes

Are there different types of stress? What are they?
Three Types of Stress Shearing , Tension and Compression Shearing Pushes a mass of rock in two opposite directions. Rock breaks, slips apart or changes its shape. Are there different types of stress? What are they?

Tension Pulls on the crust, stretching rock so that it becomes thinner in the middle. It occurs where two plates are moving apart.

Stress video Compression Squeezes rock until it breaks. One plate pushing on another compresses rock like a trash compactor.

What are faults? Where do they occur?
Fault: A break in Earth’s crust where slabs of crust slip past each other. Faults occur when enough stress builds up in rock to make it break.

Describe and draw the three types of Faults.
1) Strike Slip Faults Found at transform boundaries The rocks on either side of the fault slip past each other sideways with little up or down motion Ex: San Andreas Fault.

strike slip video strike-slip fault animation

What is the difference between a hanging wall and a footwall?
normal fault animation Normal Faults Found at divergent boundaries. Tension forces in Earth’s crust cause normal faults. The fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault. There is up and down motion. Hanging Wall lies above Footwall  lies below

Normal Fault Animation

Reverse Faults. Found at convergent boundaries The same structure as a normal fault, but the blocks move in the opposite direction. The rock forming the hanging rock slides UP & OVER the foot wall.

reverse fault animation

Fault animation More Animation

Type of Stress Type of Plate Boundary Type of Fault