EARTHQUAKES AND EARTH

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EARTHQUAKES AND EARTHS INTERIOR
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Objectives

• Explain the connection between earthquakes and
  plate tectonics.
• Identify several earthquake-related hazards.
• Define body waves and surface waves.
• Explain how the materials in Earths interior
  affect seismic waves.
• Define and describe the composition of Earths
  crust, mantle and core.

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Megathrust earthquakes
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Earthquakes and earthquake hazards

• Seismology
• The scientific study of earthquakes and seismic
  waves
• Seismic waves
• An elastic shock wave that travels outward in all
  directions from an earthquakes source
• Seismic creep

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Earthquakes and plate motion

• The elastic rebound theory
• Continuing stress along a fault
• Results in buildup of elastic energy in the rocks
• Energy abruptly released when an earthquake occurs

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Earthquakes and plate motion
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Earthquake Hazards and Predictions

• Primary hazards
• Collapsing buildings, bridges and other
  structures
• Aftershock
• Secondary hazards
• Landslides, fires, ground liquefaction, tsunamis

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Earthquake hazards
Landslide, Huascaran, Peru
Open fissure, Golcuk, Turkey
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Earthquake hazards
Fire, San Francisco, California
Ground liquification, Niigata, Japan
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The Sumatra-Andaman Tsunami (2004)
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Earthquake prediction

• Short-term prediction and early warning
• Precursor phenomena
• Foreshocks
• Long-term forecasting
• Paleoseismology
• The study of prehistoric earthquakes
• Seismic gaps

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Earthquake Readiness

• Preparation and readiness to earthquakes key to
  reducing fatalities
• Reinforced structures
• Bolting wood-framed buildings to foundation
• Protecting utility lines from movement
• Education

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The Science of Seismology

• Seismograph
• An instrument that detects and measures
  vibrations of Earths surface
• Advanced seismographs detect vibrations 10-8 of a
  centimeter
• Seismogram
• The record made by a seismograph

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The Science of Seismology
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Seismic waves

• Body wave
• Travels through Earths interior
• Surface wave
• Travels along Earths surface
• Focus
• Where rupture commences and an earthquakes
  energy is first released

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Locating earthquakes

• Compressional wave
• Wave consisting of alternating pulses of
  compression and expansion
• Can pass through any medium (solids, liquids,
  gases)
• P (or primary) wave
• Shear wave
• Rock is subjected to side to side or up and down
  forces, perpendicular to waves direction of
  travel
• S (secondary) wave
• Not transmitted through water
• Travel slower than P waves

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Locating earthquakes
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Locating earthquakes
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Locating earthquakes

• Epicenter
• The point on Earths surface directly above an
  earthquakes focus

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Locating earthquakes
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Measuring Earthquakes

• The Richter Magnitude Scale
• A scale of earthquake intensity based on the
  recorded heights, or amplitudes, of the seismic
  waves recorded on a seismograph
• A logarithmic scalea 10 fold increase in
  amplitude for each unit
• Moment Magnitude Scale
• A measure of earthquake strength that is based on
  the rupture size, rock properties, and amount of
  displacement on the fault surface

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Measuring Earthquakes
Richter magnitude 7
Richter magnitude 6
Richter magnitude 8
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Studying Earths Interior

• Seismic discontinuity
• A boundary inside Earth where the velocities of
  seismic waves change abruptly

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Studying Earths Interior
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Studying Earths Interior

• Three things can happen to seismic waves when
  they meet a boundary
• Refraction bent as they pass from one material
  to another
• Reflection some or all of the wave energy
  bounces back
• Absorption some or all of the wave energy is
  blocked

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How geologists look into Earths interior

• Seismic tomography
• Allows geologists to image inside of Earth
• Direct observation
• Drilling
• Xenoliths
• Indirect observation
• Magnetism
• Density

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Diamonds!
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A Multilayered Planet

• Crust
• The outermost compositional layer of the solid
  Earth, part of the Lithosphere
• Thickness ranges between 8 kilometers (oceanic)
  and 45 km (continental)

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A Multilayered Planet
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A Multilayered Planet

• Mantle
• The middle compositional layer of Earth, between
  the core and the crust
• Comprised primarily of olivine and pyroxene
• Asthenosphere mantle where rock is near melting
• Mantle-core boundary mesosphere

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A Multilayered Planet
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A Multilayered Planet

• Core
• Innermost layer, where the magnetic field is
  generated and much geothermal energy resides
• Separated into outer core (liquid) and inner core
  (solid)

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Critical Thinking

• If you were on a ship in the ocean, would you be
  able to feel an earthquake that occurred below
  you, on the ocean floor?
• Do you think there is no limit to the magnitude
  of earthquakes?
• What kind of wave would you expect to travel
  faster a seismic wave or a tsunami wave?