Earthquake: the shaking of the Earth’s crust caused by a release of energy.

Common cause: movement of the Earth’s plates

As the Earth’s plates move past one another, friction causes the plates to get “stuck”.· Stress and pressure builds up and causes the plate to become deformed (bend) as it continues to try and move (the plates are elastic-they can change shape).· Eventually, the pressure is great enough to overcome the friction and the plates slip past one another.· The plate movement is the earthquake. The greater the plate movement, the larger the earthquake.· The plates are in a new location, but they go back to their original shape (rebound).

**Think of pushing on the ends of a wooden ruler. As you push, the ruler will bend. When you release the pressure on the ends, the ruler snaps back to its original shape.

Fault: break in the lithosphere along which movement has occurred

Focus: the point at which the first movement occurs

Epicenter: the point on Earth’s surface directly above the focus

Friction prevents plate movement most of the time. Boundary Type vs. Earthquake Depth:

a. divergent boundaries: within 30 kilometers of the surface

b. transform boundaries: occur at shallow depths

c. subduction boundaries: occur as deep as 700 km

Body wave: travels from the focus of an earthquake through Earth

P-wave: a body wave that squeezes and stretches rock materials

- also known as a compression wave or a primary wave

- P-waves can travel through any material- solid, liquid or gas

S-wave: a body wave that causes particles of rock to move at right angles

-also known as shear waves or as secondary waves

-can travel through only solids, not liquid or gas

P and S waves

Surface wave: a wave that travels along Earth’s surface- caused by body waves

Surface waves cause considerable damage

The rate at which P waves and S waves travel depends on the type and density of the material through which they travel

The waves move faster when material is rigid and dense

S waves travel at a little less than half the speed of P waves

Surface waves travel the slowest when compared to P and S waves