Chapter 12Chapter 12
Section 1Section 1
•Earthquakes are caused by a suddenrelease of energy when rocks move alonga fault.
•Elastic rebound is thought to cause therocks 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 deep
Shallow foci cause the most damage
Seismic WavesSeismic Waves
Body Waves:Body Waves:
Travel through the EarthTravel through the Earth
Made up of:Made up of:
-P waves: primary, fastest-P waves: primary, fastest
-S waves: secondary, second fastest, travelthrough solids only-S waves: secondary, second fastest, travelthrough solids only
Earthquake Waves & Earth’s InteriorEarthquake Waves & Earth’s Interior
Seismic Waves and the Earth’sInteriorSeismic Waves and the Earth’sInterior
The speed and direction of seismic waves givesus information about the Earth’s structureThe speed and direction of seismic waves givesus information about the Earth’s structure
Waves travel at different speeds throughdifferent materialsWaves travel at different speeds throughdifferent materials
Shadow Zones-areas where no body waves aredetectedShadow Zones-areas where no body waves aredetected
Comparing Seismic WavesComparing Seismic Waves
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:
-Rayleigh-Rayleigh
-Love-Love
Earthquakes and Plate TectonicsEarthquakes and Plate Tectonics
Most earthquakes occur at plate boundaries(converging and diverging) where the stress isthe greatestMost earthquakes occur at plate boundaries(converging and diverging) where the stress isthe greatest
How do scientists calculate how far a locationis from the epicenter of an earthquake?How do scientists calculate how far a locationis from the epicenter of an earthquake?
Scientists calculate the differencebetween arrival times of the P wavesand S wavesScientists calculate the differencebetween arrival times of the P wavesand S waves
The further away an earthquake is, thegreater the time between the arrival ofthe P waves and the S wavesThe further away an earthquake is, thegreater the time between the arrival ofthe P waves and the S waves
How Seismographs or SeismometersWork, TB pg. 217How Seismographs or SeismometersWork, TB pg. 217
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
TypicalSeismogram-a graphical illustrationof EQ wavesTypicalSeismogram-a graphical illustrationof EQ waves
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 the groundSeismographs record vibrations in the ground
Magnitude: the strength of an earthquake,Richter scale or moment magnitude (moreaccurate)Magnitude: the strength of an earthquake,Richter scale or moment magnitude (moreaccurate)
Intensity (amount of damage)-modified Mercalliscale-from I-XIIIntensity (amount of damage)-modified Mercalliscale-from I-XII
How are Earthquakes Measured?Richter ScaleHow are Earthquakes Measured?Richter Scale
How are Earthquakes Measured?Mercalli Intensity ScaleHow are Earthquakes Measured?Mercalli Intensity Scale
Click Link for Interactive Demohttp://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf
Tsunamis can form when the epicenter is on theocean floorTsunamis can form when the epicenter is on theocean floor
Damage to structures depends on how they arebuilt and what type of ground they sit onDamage to structures depends on how they arebuilt and what type of ground they sit on
Predicting EarthquakesPredicting Earthquakes
No reliable way to predict earthquakesNo reliable way to predict earthquakes
Scientists are trying to detect changes that occurbefore an earthquakeScientists are trying to detect changes that occurbefore an earthquake
Seismic gaps are areas of low earthquake activity,but have a history of strong activity-might bespot for future earthquakeSeismic gaps are areas of low earthquake activity,but have a history of strong activity-might bespot for future earthquake
Foreshocks-small earthquakes that precede alarge earthquakeForeshocks-small earthquakes that precede alarge earthquake
