What are Seismic Waves?What are Seismic Waves?

Types of Waves: Seismic Types of Waves: Seismic WavesWaves

We will be covering:We will be covering:Body WavesBody Waves

• Primary or p-wave Primary or p-wave – Compression waveCompression wave

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

Surface WavesSurface Waves• Love waveLove wave• Rayleigh waveRayleigh wave

Seismic WaveSeismic Wave

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

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

Body WavesBody Waves

• P Waves (compression wave)P Waves (compression wave)• The first kind of body wave is the The first kind of body wave is the P waveP wave or or primary primary

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

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

thunder and heard the windows rattle thunder and heard the windows rattle at the same timeat the same time? ?

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

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

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

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

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

Surface WavesSurface Waves• Rayleigh WavesRayleigh Waves• The other kind of surface wave is the The other kind of surface wave is the Rayleigh waveRayleigh wave, named for , named for

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

LET’S CONCLUDE WITH SOME VISUAL AIDS!LET’S CONCLUDE WITH SOME VISUAL AIDS!

EARTHQUAKE WAVESEARTHQUAKE WAVES• 3 types of seismic waves show up on seismogram3 types of seismic waves show up on seismogram

– P wavesP waves: shake earth in same direction as : shake earth in same direction as wave; wave; travel thru solid, liquid, gastravel thru solid, liquid, gas

– S wavesS waves: Shake earth sideways to wave : Shake earth sideways to wave direction; direction; travel thru solids onlytravel thru solids only

– Surface waves: circular movement of rock; : circular movement of rock; travel on surface – cause most damage!!travel on surface – cause most damage!!

EARTHQUAKE WAVESEARTHQUAKE WAVES

P waves move through solids & liquids

S waves move through solids only!!!

EARTHQUAKE WAVESEARTHQUAKE WAVESBody P waves S waveswaves

AKA

Moves through

Movement of rock

Primary (1st to arrive)

Longitudinal, Compression

all states of matter (solid, liquid, gas)

back and forth movement of rock• push/pull or compression/stretch out• Like slinky down stairs

Vibration is same as the direction of travel

Secondary (2nd to arrive - larger)

Transverse, Shear

Can go through solids only

Move sideways • perpendicular to direction of wave

travel• Like snake