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Chapter 11 Earthquakes

Chapter 11 Earthquakes






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    Chapter 11 Earthquakes Chapter 11 Earthquakes Presentation Transcript

    • Chapter 11 Earthquakes
    • When rocks break they move along faults.
    • Applied forces cause rocks to undergo elastic deformation.
    • When elastic limits are passed, rocks break.
    • Rock on one side of a fault can move up, down, or sideways in relation to rock on the other side of the fault.
    • Faults occur because forces inside the Earth cause earth’s plates to move placing stress on or near the plate edge
    • Rocks will bend, compress, stretch, and possibly break.
    • Earthquake: vibrations produced by breaking rock
    • Rocks break, move along the fault, and return to original shapes.
    • Rock on one side of a fault can move over, under, or past each other along fault lines.
    • Three types of forces act on rocks: tension, compression, and shear.
    • Tension forces; normal fault: caused by rock above the fault moving downward in relation to the rock below the fault.
    • Reverse fault: compression forces squeeze rock above the fault up and over the rock below the fault.
    • Created by shear forces; strikeslip fault: rocks on either side of the fault move past each other without much upward or downward motion.
    • Section 2:
    • Seismic – waves generated by an earthquake can move the ground forward and backward, up and down, and side to side.
    • Focus: an earthquake’s point of energy release
    • Primary waves (P waves): cause particles in rocks to move back and forth in the same direction that the wave is traveling.
    • Secondary waves (S waves) – cause particles in rock to move at right angles to the direction of wave travel.
    • Surface waves – move rock particles in a backward, rolling motion and a sideways swaying motion.
    • The point on the Earth’s surface directly above the earthquake focus is called the epicenter.
    • The different speeds of seismic waves allow scientists to determine the epicenter.
    • Primary waves move the fastest. Secondary waves follow Surface waves move slowest and arrive at the seismograph station last.
    • Seismograph: measures seismic waves.
    • Consists of a rotating drum of paper and a pendulum with an attached pen.
    • The paper record of a seismic event is called a seismogram.
    • Earth’s structure consists of an inner, mostly iron, solid core surrounded by a mostly iron liquid outer core surrounded by the mantle.
    • The curst is Earth’s outer layer, about 5 to 60 km thick.
    • A seismic wave’s speed and direction change as the wave moves through different layers with various densities.
    • Density generally increases with depth as pressures increase.
    • Shadow zones do not receive seismic waves because the waves are bent or stopped by materials of different density.
    • Changes in seismic wave speed allowed detection of boundaries between Earth’s layers.
    • Although earthquakes are natural geologic events, they kill many people and cause a lot of damage
    • Seismologists
      • scientists who study earthquakes
    • Magnitude
      • measure of energy released by an earthquake
      • determined by the Richter scale and based on the height of the lines on a seismogram
    • The Richter Scale has no upper limit
    • Most earthquakes have magnitudes too low to be felt by humans – 3.0 to 4.9 on the Richter Scale
    • The modified Mercalli intensity scale describes earthquake intensity based on structural and geologic damage
    • Liquefaction
      • shaking from an earthquake can make wet soil act like a liquid
    • Ocean waves caused by earthquake are called tsunamis
      • caused when a sudden movement of the ocean floor pushes against the water
      • can travel thousands of kilometers in all directions
    • Earthquakes cannot be reliably predicted
      • Knowing how and where to plan for earthquakes can help prevent death and damage
      • Buildings can be constructed to withstand seismic vibrations
      • Flexible, circular moorings are being placed under buildings
      • made of alternating layers of rubber and steel
    • The rubber acts like a cushion to absorb earthquake waves
    • Homes can be protected by careful placement of heavy objects and securing gas appliances
    • During an earthquake, crawl under a sturdy table or desk
      • outdoors, stay away from buildings and power lines
    • After an earthquake, check for water or gas line damage leave IMMEDIATELY if a gas smell is present