You’re stressing me OUT! Stress-a force that acts on rock to change its shape or volume.

Types of Stress There are three basic types of stress… 1) Tension- This stress pulls on the crust where plates are moving apart, stretching rock to become thin in the middle. 2) Compression- This stress squeezes rock together where plates are moving toward one another, causing them to fold or break. 3) Shearing- This stress pushes rock in different directions, causing them to slip apart or change shape.

Kinds of Faults Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks. There are three main types of faults: –Normal faults –Reverse faults –Strike-slip faults

Normal Fault The fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault. Hanging wall Footwall

Reverse Faults A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

Strike-slip Faults In places where plates move past each other, shearing creates strike-slip faults. That is, the rocks on either side slip past each other sideways.

Folding Earth’s Crust A fold in rock that bends upward into an arch. A fold in rock that bends downward to form a valley.

Fault-block Mountains As tension forces pull the crust apart, two parallel normal faults can form a range of fault-block mountains.

Plateau A large area of flat land elevated high above sea level. A force in the Earth’s crust can push up a large, flat block of rock.

Earthquakes

The Earth is never still. Everyday there are several thousand earthquakes. That means, somewhere right now, there is shaking and trembling that results from the movement of rock beneath Earth’s surface. Did you just feel that?

Focus

The terms P Waves: the first to arrive. These seismic waves compress and expand the ground like an accordion. They can travel through solids and liquids. S Waves: secondary waves. These seismic waves vibrate from side to side as well as up and down. They shake the ground back and forth. They cannot move through liquids. Surface Waves: R Waves and Love Waves. When some P & S waves reach the surface they become surface waves. Love waves roll like an ocean wave and R waves move the land side to side.

Monitoring Earthquakes Seismic waves cause the seismograph's drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations.

Earthquake Safety Causes of earthquake damage include shaking, liquefaction, aftershocks, and tsunamis. The best way to protect yourself is to drop, cover, and hold.