Earth’s Crust in Motion Chapter 2.1

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. What is an earthquake? What causes earthquakes?

Where Do Earthquakes Occur and How Often? ~80% of all earthquakes occur in the circum-Pacific belt most of these result from convergent margin activity ~15% occur in the Mediterranean-Asiatic belt remaining 5% occur in the interiors of plates and on spreading ridge centers more than 150,000 quakes strong enough to be felt are recorded each year

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.

Stress Clip

Are there different types of stress? What are they? Three Types of Stress Shearing, Tension and Compression 1. Shearing Pushes a mass of rock in two opposite directions. Rock breaks, slips apart or changes its shape.

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

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

Questions: How does stress in the crust change Earth’s surface? What type of landform results from tension? What type of landform results from compression?

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.

Elastic Rebound To view this animation, click “View” and then “Slide Show” on the top navigation bar.

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. Clip-San Andreas Clip 2 Strike Slip

What is the difference between a hanging wall and a footwall? 2. 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 below Footwall  lies above Normal Fault Clip,2,3 What is the difference between a hanging wall and a footwall?

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 Clip

Faults To view this animation, click “View” and then “Slide Show” on the top navigation bar.

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.

1. Fill in the chart below (A) Type of Stress Type of Fault Type of Plate Boundary