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Understanding Earthquakes: Causes, Types, and Measurement

An earthquake is a sudden slip on a fault, resulting in ground shaking and seismic energy release. Causes include tectonic plate movements, volcanic activity, and sudden stress changes within the Earth. There are three main types of faults: strike-slip, thrust, and normal. Earthquakes are measured using various scales, including the Richter Scale and Mercalli Intensity Scale, which assess earthquake magnitude and felt intensity. This overview discusses seismic waves, earthquake mechanics, and how scientists locate and measure earthquakes along with relevant concepts like tsunamis and seismographs.

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Understanding Earthquakes: Causes, Types, and Measurement

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  1. Earthquakes Adapted from Steven Dutch, Natural and Applied Sciences,  University of Wisconsin-Green Bay L. Smith 2014

  2. What is an earthquake? • Used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip • Caused by volcanic or magmatic activity, • Caused by other sudden stress changes in the earth.

  3. Three Types of Faults Strike-Slip Thrust Normal

  4. What causes earthquakes? • Tectonic plates move past each other causing stress. Stress causes the rock to deform • Plastic deformation – does not cause earthquakes • Elastic deformation – rock stretches then reaches a breaking point, releasing energy.

  5. Elastic Rebound – deformed rock goes back to its original shape http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  6. Focus – point inside the Earth where an earthquake beginsEpicenter – point on Earth’s surface above focus

  7. How Seismographs Work the pendulum remains fixed as the ground moves beneath it http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  8. Typical Seismogram http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

  9. Primary Waves (P Waves) • A type of seismic wave that compresses and expands the ground • The first wave to arrive at an earthquake http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

  10. Secondary Waves (S Waves) • A type of seismic wave that moves the ground up and down or side to side http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

  11. Comparing Seismic Waves

  12. SurfaceWaves • Move along the Earth’s surface • Produces motion in the upper crust • Motion can be up and down • Motion can be around • Motion can be back and forth • Travel more slowly than S and P waves • More destructive

  13. Seismic Waves

  14. How do scientists calculate how far a location is from the epicenter of an earthquake? • Scientists calculate the difference between arrival times of the P waves and S waves • The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

  15. Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  16. Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  17. Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  18. How are Earthquakes Measured? Richter Scale

  19. Magnitude and Intensity Intensity • How Strong Earthquake Feels to Observer Magnitude • Related to Energy Release • Determined from Seismic Records • Rough correlation between the two for shallow earthquakes

  20. Intensity How Strong Earthquake Feels to Observer Depends On: • Distance to Quake • Geology • Type of Building • Observer! Varies from Place to Place • Mercalli Scale- 1 to 12

  21. How are Earthquakes Measured? Mercalli Intensity Scale Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

  22. Magnitude - Determined from Seismic Records Richter Scale: • Related to Energy Release • Exponential • No Upper or Lower Bounds • Largest Quakes about Mag. 8.7 • Magnitude-Energy Relation • 4 - 1 • 5 - 30 • 6 - 900: • 1 Megaton = about 7 • 7 - 27,000 • 8 - 810,000

  23. Seismic - Moment Magnitude A Seismograph Measures Ground Motion at One Instant But -- • A Really Great Earthquake Lasts Minutes • Releases Energy over Hundreds of Kilometers • Need to Sum Energy of Entire Record • Modifies Richter Scale, doesn't replace it • Adds about 1 Mag. To 8+ Quakes

  24. Earthquake Waves & Earth’s Interior

  25. Seismic Waves in the Earth http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  26. Tsunamis http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  27. Formation of a tsunami http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

  28. Tsunami Warning System http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

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