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Ch.5.less.4.what are earthquakes and how do they occur
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Ch.5.less.4.what are earthquakes and how do they occur


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  • 1. earthquak es and how do they occur? Chapter 5: Lesson 3:
  • 2. What is an It is the sudden earthquake? movement of earth’s crust.
  • 3. When layers of rock that are stuck together suddenly slip an earthquake
  • 4. When two plates slide past each other, they create a transform fault, like
  • 5. Slipping along a fault begins under the earth’s surface. (80 km – 644 km deep) The place where the slipping begins is called
  • 6. Waves of energy ripple outwards from the focus. When the waves reach the surface
  • 7. The epicenter is the point from where the waves of the earthquake spread. (People start feeling the earthquake)
  • 8. Earthquakes occur at plate boundaries (like volcanoes)
  • 9. Seismometers Instruments used to measure the waves produces by an earthquake.
  • 10. There are 3 types of seismic waves P waves (Primary waves) S waves (Secondary waves) Lg waves (Surface waves)
  • 11. P waves - Move back and forth - Fastest - Travels through solid and liquid layers of earth.
  • 12. S waves - Moves up and down. - Travel half as fast as P waves. - Travels through solid layers of earth only.
  • 13. Lg waves - Travels as ripples across earth’s surface. - Slowest. - Causes most damage.
  • 14. Lg waves P waves S waves
  • 15. Locating earthquakes Earthquake epicenter can happen any where along circumference Seismometer station 1
  • 16. The point where the 3 circles meet is the epicenter Seismometer station 1 Seismometer station 2 Seismometer station 3
  • 17. Magnitude The measure of the amount of energy released by an earthquake. Richter scale Mercalli scale
  • 18. Richter scale Measures the magnitude at the epicenter (From weakest to strongest) The Richter scale starts from 1 and each whole number has 30 times more energy than the number before it.
  • 19. Mercalli scale Measures what people felt and what happens to things in a place On the mercalli scale earthquakes are rated from I – XII (XII is the most severe)
  • 20. Mercalli scale
  • 21. The earthquake in Pakistan on October 8, 2005 was rated XII the mercalli scale.
  • 22. Aftershock Earthquakes with lesser magnitude. (Felt after the main earthquake) Earthquakes with larger magnitudes have many aftershocks with large magnitudes.
  • 23. When earthquakes occur on the ocean floor waves of water are pushed upwards in sea the Deep in the all directions. energy is spread through the water so the waves are not tall.
  • 24. When the waves reach shallow water the energy is spread through less water. In shallow waters the waves are very tall causing tsunamis.