Normal Fault Occurs at Divergent Boundaries

How do Earthquake waves Travel?

• Energy released from moving plates and faults travels through the Earth as waves.

• These waves are called seismic waves.

Types of Seismic Waves

1. BODY WAVES: Seismic waves that travel through the Earth.2. SURFACE WAVES: Seismic waves that travel along the surface.

•WAVES TRAVEL: 1.At different speeds and2 In different ways

Depending on what kind of material they are moving through.

Body Waves

• There are two types of body waves:1.P Waves: Pressure Waves, Primary Waves• Travel through solid, liquid and gases

2.S Waves: Secondary Waves• Can’t travel through liquid

P- Waves• P-waves are the fastest waves.• P-waves are the first waves to be detected and the first waves to arrive.• P-waves are also called primary waves because they arrive first.• P-waves cause rock to squeeze and stretch. Imagine a slinky!

• The area of the Earth that does not receive seismic energy is called the shadow zone.

S- Waves• S-waves are the second fastest waves.• S-waves are also called secondary waves because they arrive

second.• S-waves are slower than P-waves.• S-waves move rock from side to side.

• S-waves can’t travel through parts of the Earth that are completely liquid.

Surface Waves• Surface waves move along the

surface of the Earth.

• Surface waves can move up,

down and around or side to side.

• Surface waves move the slowest

and cause the most destruction.

• Third to Arrive

Shadow Zone

The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.

Earthquake Measurement• A seismograph is an instrument used by scientists to measure earthquakes.• Seismologists who study earthquakes can determine when an earthquake

started by noting the arrival times of P-waves and S-waves.• A seismograph records vibrations in the Earth and determines the strength and

location of an earthquake.

Measuring Earthquakes• The Richter Scale measures magnitude.• The measurements are given in numbers.• Measures the energy released by an earthquake

Earthquake Severity-Energy released by an earthquake. Richter Earthquake Magnitudes Effects (Severity Increases 10 fold for every 1 pt)

• Less than 3.5 Generally not felt, but recorded. • 3.5-5.4 Often felt, but rarely causes damage.• Under 6.0 At most slight damage to well-designed buildings. Can cause major damage

to poorly constructed buildings over small regions.• 6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people

live. • 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. • 8 or greater Great earthquake. Can cause serious damage in areas several hundred

kilometers across.