Download - Earthquakes
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Earthquakes
And Earth’s Structure
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Earth’s Structure
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Origin of the Earth
• Meteors and Asteroids bombarded the Earth
• Gravitational compressionGravitational compression
• Density Stratified planetDensity Stratified planet
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Earth’s Interior• CoreCore
– densedense– Iron and NickelIron and Nickel– Inner CoreInner Core - solid - solid– Outer CoreOuter Core - liquid - liquid
– Less dense than coreLess dense than core– Iron and Magnesium silicatesIron and Magnesium silicates– Mostly solidMostly solid– Upper mantle is partially moltenUpper mantle is partially molten
• MantleMantle
– Outermost layerOutermost layer– Very thin and rigidVery thin and rigid– ContinentalContinental – granite – granite
– Density = 2.8 g/cmDensity = 2.8 g/cm33
– OceanicOceanic – basalt – basalt– Density = 3.0 g/cmDensity = 3.0 g/cm33
• CrustCrust
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Evidence of Internal Structure
Granite• DensityDensity
– calculate density of Earthcalculate density of Earth– Speculate on probable compositionsSpeculate on probable compositions
Basalt
• MeteoritesMeteorites– Use composition and age to Use composition and age to
determine composition and determine composition and age of Earthage of Earth
• Seismic wavesSeismic waves– Travel times and direction Travel times and direction
give indication of internal give indication of internal structure of Earth structure of Earth
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Types of Seismic Waves
• S wavesS waves
• P wavesP waves– Primary wavesPrimary waves
– Push and pull movementPush and pull movement
– Travel fastest (Travel fastest (~ 6 km/sec)~ 6 km/sec)
– Travel thru solids and liquidsTravel thru solids and liquids
– Secondary wavesSecondary waves
– Move side-to-sideMove side-to-side
– Slower (~ 4 km/sec)Slower (~ 4 km/sec)
– Travel thru solids onlyTravel thru solids only
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Seismic Waves Through Earth
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What is an Earthquake?
• The vibration of Earth produced by the rapid release of energy
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Elastic Rebound Theory
• The crust will first bend• When the stress exceeds strength of the rock, it will
“snap” into a new position• In the process of breaking, “seismic waves are released
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Parts of an Earthquake
•Focus
•Epicenter
•Energy released radiates in all directions from the focus•Energy is in the form of waves – “seismic waves”
– Location on surface directly above the focus
–place within earth where EQ originate
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How Do We Locate an Epicenter?
• Instruments around the world record EQ
•Record Earth movements by stationary mass on rotating drum
•Use seismogram to:– Locate an epicenter– Determine magnitude
Seismograph
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Seismogram
•Measure the distance between P- and S-waves– This is the time difference in arrival times
•Help determine the epicenter
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Locating the Epicenter
• Plot the time difference on y-axis (time interval)
• Trace plot to blue line to determine distance to epicenter
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Locating an Epicenter Triangulation
• A minimum of 3 seismic stations are needed to determine the epicenter
• Measure that distance around the seismic station
• The epicenter may be located anywhere on that line
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Determining Magnitude
• Measure the amplitude of the strongest wave
•The amplitude is the height on paper
•Plot distance between p- and s-wave
•Plot amplitude
• Connect plots to determine magnitude
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You are now a Seismologist!!
Virtual Earthquake Introduction:http://vcourseware5.calstatela.edu/VirtualEarthquake/VQuakeExecute/htm
Virtual Earthquake:
http://sciencecourseware.org