Earthquakes!Earthquakes!

How does an earthquakes form?How does an earthquakes form?

Forces inside the earth put stress on the Forces inside the earth put stress on the rocks near plate edges. Stress cause rocks near plate edges. Stress cause rocks to bend and stretch rocks to bend and stretch

Rocks bent past their elastic limit = rock Rocks bent past their elastic limit = rock break and move along surfaces called break and move along surfaces called faultsfaults

Friction within the faults cause the release Friction within the faults cause the release of energy making an earthquakeof energy making an earthquake

Three types of forces that Three types of forces that create faults create faults

Tension: pull apartTension: pull apart

Compression: push togetherCompression: push together

Shear: slide past Shear: slide past

Normal FaultNormal Fault

TensionTension forces pull rock forces pull rock apartapart

A rock above the fault A rock above the fault surface moves downward surface moves downward in relation to rock below in relation to rock below the fault surface the fault surface

Reverse FaultsReverse Faults

CompressionCompression forces forces squeeze rocksqueeze rock

Rock above a Rock above a reverse fault surface reverse fault surface is forced up and over is forced up and over the rock below the the rock below the fault surface fault surface

Strike-Slip faults Strike-Slip faults

ShearShear forces move rocks past each other forces move rocks past each other without much vertical movement without much vertical movement

Seismic Waves General InfoSeismic Waves General Info Seismic wavesSeismic waves are the waves of energy are the waves of energy

released when rocks break along released when rocks break along faultsfaults..

FocusFocus = the point = the point within the Earth’s within the Earth’s InteriorInterior at which this energy is first at which this energy is first released.released.

Seismic waves are produced and Seismic waves are produced and travel travel outwardoutward from the earthquake focus. from the earthquake focus.

Are Seismic Waves Are Seismic Waves CompressionalCompressional or or TransverseTransverse Waves? – Why?? Waves? – Why??

EpicenterEpicenter

EQ EQ EpicenterEpicenter = the point on the Earth’s = the point on the Earth’s surface surface directly abovedirectly above the earthquake’s the earthquake’s focusfocus..

The The speeds of seismic wavesspeeds of seismic waves allows us allows us to determine how far away earthquake to determine how far away earthquake epicenter is from a seismic station.epicenter is from a seismic station. Measured with Measured with SeismographSeismograph..

““Body” WavesBody” Waves1)1) P-waves (Primary Waves)P-waves (Primary Waves)

Cause particles in rocks Cause particles in rocks to move to move back & forth in back & forth in same direction same direction ((Compressional) fastestCompressional) fastest

2)2) S-waves (Secondary Waves)S-waves (Secondary Waves) Cause particles in rocks Cause particles in rocks to move at to move at right anglesright angles to to the direction of the wave the direction of the wave travel (Transverse Wave.) travel (Transverse Wave.) slowerslower

Surface WavesSurface Waves

Move rock particles in a Move rock particles in a rolling, rolling, side-to-side, swaying motion.side-to-side, swaying motion.

Most damagingMost damaging type of seismic type of seismic waves and the Slowestwaves and the Slowest

Measuring EQ’sMeasuring EQ’s

Richter ScaleRichter Scale Used to measure the Used to measure the strengthstrength of an of an

earthquake.earthquake. Based on the Based on the height of the linesheight of the lines on on

the seismograph. the seismograph. Scale has Scale has no upper limitno upper limit, but 9.5 is , but 9.5 is

estimated maximum.estimated maximum.

Measuring EQ’sMeasuring EQ’s

Mercalli Intensity ScaleMercalli Intensity Scale Used to measure the intensity of Used to measure the intensity of

an earthquake based on the an earthquake based on the amount of damage caused by the amount of damage caused by the earthquake.earthquake.

Scale has 12 levels.Scale has 12 levels.

Earth layersEarth layers

Inner core: solid. Made of ironInner core: solid. Made of iron Outer core: liquid. Made of ironOuter core: liquid. Made of iron Mantel: liquid magma. Made of Silicon, Mantel: liquid magma. Made of Silicon,

Oxygen, MagnesiumOxygen, Magnesium Asthenosphere: upper part of the mantelAsthenosphere: upper part of the mantel

Lithosphere/crust: Solid. Made of Silicon Lithosphere/crust: Solid. Made of Silicon and Aluminumand Aluminum

How do scientist know this?How do scientist know this? Seismic wave change Seismic wave change

pathway and speed at pathway and speed at different densitiesdifferent densities

S-wave stop at the S-wave stop at the liquid outer core liquid outer core

P-wave are bent and P-wave are bent and slowed at liquid outer slowed at liquid outer core and then speed core and then speed up again in solid inner up again in solid inner corecore

PG136PG136

Tsunami Tsunami

When an earthquake occurs under water When an earthquake occurs under water the energy released can generate a large the energy released can generate a large wave that can reach 30 m high wave that can reach 30 m high