Earthquakes

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Earthquakes

• And Earths Structure

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Earths Structure
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Origin of the Earth

• Meteors and Asteroids bombarded the Earth

• Gravitational compression

• Density Stratified planet

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Earths 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

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Evidence of Internal Structure

• 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

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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

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Seismic Waves Through Earth
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Parts of an Earthquake

• Focus

• place within earth where EQ originate

• Epicenter

• Location on surface directly above focus

• Energy radiates in all directions from the focus

• Energy is in the form of waves seismic waves

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Seismic WavesLocating the Epicenter

• Seismograph

• Instruments around the world record EQ

• Records Earth movement by stationary mass on
  rotating drum

• Seismogram

• Locate an epicenter

• Determine magnitude

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Seismogram

• Help determine the epicenter

• Measure the distance between P- and S-waves
• This is the time difference in arrival times

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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

• 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

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Earthquake StrengthRichter Scale

• A measure of the strength of an earthquake or the
  amount of energy released

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Determining Magnitude

• Measure amplitude of the strongest wave

• Amplitude is the height on paper

• Plot distance between p- and s-wave

• Plot amplitude

• Connect plots to determine magnitude

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Earthquake IntensityModified Mercalli Scale

• Effects of an EQ vary from place to place

• There is only 1 magnitude, but intensity can vary

• Subjective scale

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Intensity Map Loma Prieta 1989
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Oakland, 1989

• Oakland is farther from epicenter, but scored a 9
  on Intensity Scale

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You are now a Seismologist!!

• Virtual Earthquake Introduction
• http//vcourseware5.calstatela.edu/VirtualEarthqua
  ke/VQuakeExecute/htm
• Virtual Earthquake
• http//sciencecourseware.org