Chapter 6 Key Terms TensionShear StrainJoint FaultRichter Scale SeismometerDivergent Boundary EpicenterConvergent Boundary TsunamiTransform Boundary 1

Chapter 6 EARTHQUAKES 2

Earthquake  Series of low-frequency shock waves traveling through the earth  What causes these earthquakes?  The tectonic plates 3

Plate Tectonics Theory  Earth’s crust is made up of many plates  Plates are in constant motion  Plate edges (margins) can collide  Earthquake waves are emitted from this collision 4

Forces  Stress  Force exerted inside a material  Compression  Tension  Shear  Most important in producing earthquakes 5

Boundaries  Divergent Boundaries  Margin where plates are moving away from each other  Convergent Boundaries  Margin where plates are moving toward each other  Transform Boundaries  Margin where plates slide past each other 6

Strain  Any change in shape of a solid under stress  The amount of strain a material can endure without breaking is related to its ductility  Elasticity also helps determine the magnitude of the earthquake 7

Earthquake Article  Find an article about a major earthquake that has happened in the past 50 years  Read the article and write a summary about the article  The summary must be at least 200 words  Include source at end of summary  DO NOT USE WIKIPEDIA!!!  Due December 2nd 8

Faults & Joints  Joint  Stress crack in a rock  Fault  When sections of rock on both sides of the joint move along the fracture  Formed by tectonic activity  Occur between all tectonic plates 9

Describing Faults  Strike  The direction of a fault  Dip  Angle of the fault face downward from the horizontal 10

Classifying Faults  Dip-slip Fault  Fault whose motion is parallel to its dip (up and down)  2 types of dip-slip faults  Normal Fault  When the block above the fault dropped  Reverse Fault  When the block above rises  Strike-slip Fault  Horizontal motion in the fault 11

Faults and Earthquakes  Most earthquakes that we can feel happen at depths less than 45 miles below the surface  If the rocks move easily across each other, no earthquake occurs  A “locked” fault builds up stress  When the stress becomes too much, the rocks suddenly fracture, causing a release in a large amount of energy  Aftershocks – secondary earthquakes 12

Seismology  Seismometers – detect earthquake waves  Measure both amplitude and frequency of waves 13

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Seismology  Seismometers – detect earthquake waves  Measure both amplitude and frequency of waves  Seismograph – has both seismometer and a way to record the changing waves  Seismogram – the recording from a seismograph 15

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Types of Seismic Waves  Body waves – waves that pass right through the earth  P Waves (Primus)  Fastest body waves; first to arrive  Longitudinal compression waves 18

Types of Seismic Waves  Body waves – waves that pass right through the earth  S Waves (Secundus)  Slower but stronger waves  Transverse or shear waves  Cannot pass through liquid or gas 19

Types of Seismic Waves  Surface Waves – travel along earth’s surface  Move at relatively the same speed as S waves, but are more destructive because they affect buildings on the surface 20

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Types of Seismic Waves  Surface Waves – travel along earth’s surface  Move at same speed as S waves, but are more destructive because they affect buildings on the surface  2 forms of surface waves  Rayleigh – move in a vertical, circular motion  Love – move horizontally 22

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Locating Earthquakes  Focus  Exact location of plate movement underground  Epicenter  Directly above focus on the surface 25

Locating Earthquakes  Seismologists can know exactly where an earthquake originated based on the arrival of P and S waves  Triangulation  Using 3 stations to pinpoint the location of the epicenter 26

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Locating Earthquakes  Seismologists can know exactly where an earthquake originated from based on the arrival of P and S waves  Triangulation  Using 3 stations to pinpoint the location of the epicenter  Most earthquakes happen along tectonic plate boundaries  Pacific Rim – aka “Ring of Fire”  Others can happen along fault lines 28

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Effects of Earthquakes  Richter Scale  Units of magnitude – energy released by the earth’s movement  Not a linear relationship – exponential relationship 30

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Effects of Earthquakes  Richter Scale  Units of magnitude – energy released by the earth’s movement  Not a linear relationship – exponential relationship  Each unit on the Richter scale is 31.6 times more energy  No upper limit (maximum value)  Not very accurate above magnitude 7 or from distances greater than 700 km  Moment Magnitude Scale 32

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Effects of Earthquakes  Intensity  Measure of how much damage actually results  Depends on many things  Richter scale magnitude  Depth of focus  Damage done to buildings  Duration  Modified Mercalli Intensity Scale (MMI)  From I – XII  XII is most destructive 34

Earthquake Hazards  Building collapse  Fire  Tsunamis  Landslides 35

Earthquake prediction  Even with all the technology, we cannot predict earthquakes  Scientists study earthquakes and where they happen to chart earthquake prone regions  Even with much information, we still cannot predict the day or hour an earthquake will happen 36