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Earthquakes

Learn about earthquakes and their causes, waves, measurement, and locating epicenters. Explore the Elastic Rebound Hypothesis and the effects of foreshocks and aftershocks.

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Earthquakes

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  1. Earthquakes Chapter 8.1/8.2

  2. What is an Earthquake? Earthquake – a vibrationof the Earth produced by a rapid release of energy. Most often caused by slippage along a TRANSFORM FAULTboundary.

  3. Earthquake Basics! • When the fault “snaps”. . . Energy travels out from the focus in waves like ripples in water. • Waves travel in ALL directions • P waves, S waves, Surface waves

  4. Earthquake Waves • Two types– BODY waves and SURFACE waves • BODY WAVES – waves that travel through the Earth’s interior. • Two kinds: P-waves and S-waves. • P-waves (push-pull waves) • Move things forward and back • S-waves (shake waves) • Move things up and down

  5. Seismic Wave Motion with Surface Effects

  6. Earthquake Waves • Surface Waves– waves that travel along the Earth’s surface • Surface waves travel up and down AND side to side AT THE SAME TIME! • Surface waves are the MOST DESTRUCTIVEof all the seismic waves

  7. Seismic Wave Motion

  8. Epicenter: point on surface above earthquake focus Focus: point of rupture within Earth

  9. What Causes an Earthquake? • Elastic Rebound Hypothesis • 1. As two plates are sliding past each other, they get STUCK and stop moving. • 2. The convection current belowDOES NOT STOP, so pressure builds up under the crust. • 3. When TOO MUCHpressure has built up the crust plates shift rapidly to release the pressure. This is an EARTHQUAKE!

  10. Foreshocks vs. Aftershocks Foreshocks– small earthquakes that come days, weeks or even years before the MAIN quake. Aftershocks – small earthquakes that follow a MAIN quake. Aftershocks can cause MAJOR damage (even though they are smaller than the MAIN quake) because the main quake has already weakenedall the structures.

  11. Measuring Earthquakes • Seismology – the study of earthquake waves • Has been going on for almost 2000 years • Seismograph – the instrumentused to measure the strength of an earthquake

  12. How a Seismograph Works http://www.youtube.com/watch?v=83GOKn7kWXM&feature=endscreen&NR=1 http://www.youtube.com/watch?v=Gbd1FcuLJLQ The machine is attached to the Earth The Earth moves during an earthquake – moving the machine as well. The hanging weight DOES NOT MOVE!! Attached to the weight is a pen. As the paper moves back and forth with the machine, the pen marks the paper, recording the strength of the seismic waves.

  13. Seismograph Used to measure Seismic Waves

  14. Seismic Wave Speeds • In order from FASTESTto SLOWEST • P-waves (PRIMARY – first) • S-waves (SECONDARY – second) • Surface waves (last) • The difference in wave speedsgive us the information to determine two important measurements: • 1. How far away from the seismograph the earthquake is • 2. Where the epicenter of the earthquake is

  15. Seismogram The paper print outfrom the seismograph Shows the arrival timesof P-waves, S-waves and Surface waves

  16. 8.7 Earthquake - Sumatra November 10, 2010

  17. Earthquake Distance from Seismograph • How to calculate distance • 1. Read seismogram to determine the time interval between 1st P-wave and 1st S-wave • 5 minutes

  18. 2. Find on the time-travel graph where 5 minutes is the interval 3. Travel to the X-axis, this is the earthquake distance You now know how far away from the seismograph the epicenter is. But you DO NOTknow the DIRECTION Could be North, South, East or West How do you locate EXACT location of epicenter?

  19. EXACT Epicenter Location 1. Determine the distance from 3different seismographs 2. Draw circles that have a radius of that distance 3. The ONE PLACE that all 3 circles touch is the epicenter

  20. Locating an epicenter activity Read the directions carefully before you do any thing Complete the assignment with a partner Each student must turn in the results and analysis questions answers. This assignment will be graded as a test

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