What are Seismic Waves?

Types of WavesTypes of Waves• Compression wave

(longitudinal) • Transverse Wave

• Seismic Wave– Body Waves• Primary or p-wave Primary or p-wave –Compression waveCompression wave

• Secondary or s-wave Secondary or s-wave –Transverse waveTransverse wave

– Surface• Love waveLove wave• Rayleigh waveRayleigh wave

Seismic WaveSeismic Wave• Seismic waves are the waves of

energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.

• There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are – body waves

–surface waves

How Seismographs WorkThe pendulum remains fixed as the ground moves beneath it.

Typical Seismogram

Body WavesBody Waves• P Waves (compression wave)• The first kind of body wave is the P wave or

primary wave. This is the fastest kind of seismic wave. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air.

Primary Waves (P Waves)

• A type of seismic wave that compresses and expands the ground

• The first wave to arrive at an earthquake

Stop and Think• Have you ever heard a big clap of

thunder and heard the windows rattle at the same time?

• The windows rattle because the sound waves were pushing and pulling on the window glass much like P waves push and pull on rock. Sometimes animals can hear the P waves of an earthquake. Usually we only feel the bump and rattle of these waves.

Body WavesBody Waves• S wave (transverse wave)• The second type of body wave is the S wave

or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock. This wave moves rock up and down, or side-to-side.

Secondary Waves (S Waves)• A type of seismic wave that moves the

ground up and down or side to side

Comparing Seismic Waves

Surface Waves• Move along the Earth’s surface• Produces motion in the upper crust–Motion can be up and down–Motion can be around–Motion can be back and forth

• Travel more slowly than S and P waves• More destructive• Types:– Love– Rayleigh

Surface Waves • Love Waves • The first kind of surface wave is called a Love

wave, named after A.E.H. Love, a British mathematician who worked out the mathematical model for this kind of wave in 1911. It's the fastest surface wave and moves the ground from side-to-side.

Surface Waves• Rayleigh Waves• The other kind of surface wave is the Rayleigh

wave, named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.

Earthquakes

What is an earthquake?

• Used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip

• Caused by volcanic or magmatic activity,

• Caused by other sudden stress changes in the earth.

What causes earthquakes?

• Tectonic plates move past each other causing stress. Stress causes the rock to deform

Focus – point inside the Earth where an earthquake begins

Epicenter – point on Earth’s surface above focus

How do scientists calculate how far a location is from the epicenter of an earthquake? • Scientists calculate the difference

between arrival times of the P waves and S waves

• The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

Locating Earthquakes

Locating Earthquakes

Locating Earthquakes

How are Earthquakes Measured? Richter Scale

How are Earthquakes Measured? Mercalli Intensity

Scale

Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

Earthquake Waves & Earth’s Interior

Seismic Waves in the Earth

Tsunamis

Formation of a Tsunami

Tsunami Warning System

Now it is your turn!!• Click on the following link: • http://www.sciencecourseware.com/eec/Earthquake/EpicenterMagnitude/

• Now start activity using handout at end of notes.

• You must use the following code – For 3rd period use

• 2113714– For 4th period use

• 2113861- For 6th period use

- 2113947

Assignment due by Tues March 26 by end of class!