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Earthquakes and Seismic Waves

Earthquakes and Seismic Waves. Introduction. Earthquake = the shaking and trembling that results from movement of rock beneath Earth’s surface Focus = area beneath Earth’s surface where rock under stress breaks and causes an earthquake

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Earthquakes and Seismic Waves

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  1. Earthquakes and Seismic Waves

  2. Introduction • Earthquake = the shaking and trembling that results from movement of rock beneath Earth’s surface • Focus = area beneath Earth’s surface where rock under stress breaks and causes an earthquake • Epicenter = point on the surface directly above the focus

  3. Seismic Waves A. Earthquakes produce vibrations called Waves. B. Waves carry energy. C. Seismic waves are vibrations that travel through Earth carrying energy released during an earthquake.

  4. Waves D. Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior and across the surface. E. Three main categories of Waves: Primary Waves (P waves) Secondary Waves (S waves) Surface Waves

  5. Waves • The first waves to arrive are Primary waves. • P waves compress and expand the ground. • After P waves come Secondary waves. • S waves are seismic waves that vibrate from Side to Side as well as up and down. • When P waves reach the surface, some of them become Surface waves. • Surface waves move more slowly than P or S waves but they produce severe ground movements.

  6. Seismic Wave Speeds

  7. Waves

  8. Measuring Earthquakes • There are at least 3 different measures for rating earthquakes. • Two methods for measurement: • Mercalli Scale • Richter Scale • Mercalli Scale = Rate earthquakes on the level of damage at a certain place

  9. Mercalli Scale

  10. Richter Scale • Richter Scale = rating of an earthquake’s magnitude based on the size of the earthquake’s seismic waves • Magnitude is a number geologists assign to an earthquake based on the earthquake’s size • the seismic waves are measured by a seismograph

  11. Richter Scale

  12. Comparing Magnitudes • Comparing Magnitudes • An earthquake’s magnitude tells Scientists how much energy was released by the earthquake • Earthquakes with a Magnitude of 6 cause? • Moderate damage • 32 times the energy of a Magnitude 5 Quake

  13. Locating the Epicenter • Geologists use seismic waves to locate an earthquake’s epicenter.

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