EARTHQUAKES!EARTHQUAKES!Video: Earthquakes Video: Earthquakes

101101Chapter 12Chapter 12

Section 1Section 1

• Earthquakes are caused by a sudden release of energy when rocks move along a fault.

• Elastic rebound is thought to cause the rocks to move.

Anatomy of an EarthquakeAnatomy of an Earthquake

• Focus-location of first motion in Earth• Epicenter-spot on surface above the focus

The focus can be shallow or deepShallow foci cause the most damage

Seismic WavesSeismic WavesBody WavesBody Waves:: Travel through the EarthTravel through the Earth Made up of:Made up of:

--P wavesP waves: primary, fastest: primary, fastest--S wavesS waves: secondary, second fastest, : secondary, second fastest, travel through solids onlytravel through solids only

Earthquake Waves & Earthquake Waves & Earth’s InteriorEarth’s Interior

Seismic Waves and the Seismic Waves and the EarthEarth’’s Interiors Interior

The speed and direction of seismic The speed and direction of seismic waves gives us information about waves gives us information about the Earththe Earth’’s structures structure

Waves travel at different speeds Waves travel at different speeds through different materialsthrough different materials

Shadow Zones-areas where no body Shadow Zones-areas where no body waves are detectedwaves are detected

Comparing Seismic Comparing Seismic WavesWaves

Seismic Waves (cont)Seismic Waves (cont)Surface WavesSurface Waves Slowest moving wavesSlowest moving waves May cause the greatest damageMay cause the greatest damage 2 Types:2 Types:

--RayleighRayleigh--LoveLove

Earthquakes and Plate Earthquakes and Plate TectonicsTectonics

Most earthquakes occur at plate Most earthquakes occur at plate boundaries (converging and boundaries (converging and diverging) where the stress is the diverging) where the stress is the greatestgreatest

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

Scientists calculate the difference Scientists calculate the difference between arrival times of the P waves between arrival times of the P waves and S wavesand S waves

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

How Seismographs or How Seismographs or Seismometers Work, TB pg. Seismometers Work, TB pg.

217217

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

the pendulum remains Video link:http://www.cleanvideosearch.com/media/action/yt/watch?v=Gbd1FcuLJLQground moves beneath it

-measures ground motion and can be used to determine the distance seismic waves travel

Typical Typical Seismogram-Seismogram-

a graphical a graphical illustration of EQ illustration of EQ

waveswaves

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

Locating EarthquakesLocating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating EarthquakesLocating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating EarthquakesLocating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Section 2Section 2 Seismographs record vibrations in Seismographs record vibrations in

the groundthe ground Magnitude: the strength of an Magnitude: the strength of an

earthquake, Richter scale or moment earthquake, Richter scale or moment magnitude (more accurate)magnitude (more accurate)

Intensity (amount of damage)-Intensity (amount of damage)-modified Mercalli scale-from I-XIImodified Mercalli scale-from I-XII

How are Earthquakes How are Earthquakes Measured? Richter ScaleMeasured? Richter Scale

How are Earthquakes How are Earthquakes Measured? Mercalli Intensity Measured? Mercalli Intensity

ScaleScale

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

Section 3Section 3Video: Tsunamis 101Video: Tsunamis 101

Tsunamis can form when the Tsunamis can form when the epicenter is on the ocean floorepicenter is on the ocean floor

Damage to structures depends on Damage to structures depends on how they are built and what type of how they are built and what type of ground they sit onground they sit on

Predicting EarthquakesPredicting Earthquakes No reliable way to predict earthquakesNo reliable way to predict earthquakes Scientists are trying to detect changes Scientists are trying to detect changes

that occur before an earthquakethat occur before an earthquake Seismic gaps are areas of low Seismic gaps are areas of low

earthquake activity, but have a history earthquake activity, but have a history of strong activity-might be spot for of strong activity-might be spot for future earthquakefuture earthquake

Foreshocks-small earthquakes that Foreshocks-small earthquakes that precede a large earthquakeprecede a large earthquake