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Earthquakes

Earthquakes. And Earth’s Structure. Earth’s Structure. Origin of the Earth. Meteors and Asteroids bombarded the Earth. Gravitational compression. Density Stratified planet. Earth’s Interior. Core. dense. Iron and Nickel. Inner Core - solid. Outer Core - liquid. Mantle.

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Earthquakes

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  1. Earthquakes And Earth’s Structure

  2. Earth’s Structure

  3. Origin of the Earth • Meteors and Asteroids bombarded the Earth • Gravitational compression • Density Stratified planet

  4. Earth’s Interior • Core • dense • Iron and Nickel • Inner Core - solid • Outer Core - liquid • Mantle • Less dense than core • Iron and Magnesium silicates • Mostly solid • Upper mantle is partially molten • Crust • Outermost layer • Very thin and rigid • Continental – granite • Density = 2.8 g/cm3 • Oceanic – basalt • Density = 3.0 g/cm3

  5. Evidence of Internal Structure Granite Basalt • Density • calculate density of Earth • Speculate on probable compositions • Meteorites • Use composition and age to determine composition and age of Earth • Seismic waves • Travel times and direction give indication of internal structure of Earth

  6. Types of Seismic Waves • P waves • Primary waves • Push and pull movement • Travel fastest (~ 6 km/sec) • Travel thru solids and liquids • S waves • Secondary waves • Move side-to-side • Slower (~ 4 km/sec) • Travel thru solids only

  7. Seismic Waves Through Earth

  8. What is an Earthquake? • The vibration of Earth produced by the rapid release of energy

  9. 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

  10. Parts of an Earthquake • Focus • place within earth where EQ originate • Epicenter • Location on surface directly above the focus • Energy released radiates in all directions from the focus • Energy is in the form of waves – “seismic waves”

  11. How Do We Locate an Epicenter? • Instruments around the world record EQ Seismograph • Record Earth movements by stationary mass on rotating drum • Use seismogram to: • Locate an epicenter • Determine magnitude

  12. Seismogram • Measure the distance between P- and S-waves • This is the time difference in arrival times • Help determine the epicenter

  13. Locating the Epicenter • Plot the time difference on y-axis (time interval) • Trace plot to blue line to determine distance to epicenter

  14. Locating an Epicenter Triangulation • Measure that distance around the seismic station • The epicenter may be located anywhere on that line • A minimum of 3 seismic stations are needed to determine the epicenter

  15. 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

  16. You are now a Seismologist!! Virtual Earthquake Introduction: http://vcourseware5.calstatela.edu/VirtualEarthquake/VQuakeExecute/htm Virtual Earthquake: http://sciencecourseware.org

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