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Understanding Earthquakes: Causes, Types, and Measurements Explained

This comprehensive guide explores what earthquakes are, detailing the sudden slips on faults and the ground shaking that results. It discusses the types of faults (normal, reverse, and strike-slip) and how tectonic plate movements cause stress and subsequent earthquakes. Additionally, learn how scientists measure earthquakes using seismographs and scales like Richter and Mercalli. The guide is enriched with animations, diagrams, and distribution maps of significant earthquakes, providing an insightful overview of this natural phenomenon and its implications.

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Understanding Earthquakes: Causes, Types, and Measurements Explained

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  1. Earthquakes What Is An Earthquake? Click here to find out

  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 plate activity, http://eqseis.geosc.psu.edu The map above shows the distribution of earthquakes with magnitudes greater than 5.0 that occurred between 1965 and 1995.

  3. Three Types of Faults Animation of fault movement Strike-Slip Reverse Normal

  4. Normal fault Pulls on the crust stretching rock so that it becomes thinner (like pulling on bubble gum) = tension Occurs when plates are moving apart Hanging wall Foot wall Results in hanging wall slipping downward animation

  5. What type of fault? normal Hanging wall Foot wall http://www.bgs.ac.uk/eqr/GeoD_Structures.htm

  6. What causes earthquakes? • Tectonic plates move past each other causing stress. Stress causes the rock to deform • What type of fault boundary is this? • What type of stress is shown? transform shearing

  7. Strike – slip fault Rocks on either side of fault slip past each other sideways with little up or down motion - What type of stress is produced? shearing Occurs at a plate boundary transform Animation of strike-slip motion

  8. Fault rupture across road in western Kaynasli, right-lateral strike slip displacement was about 4.0 m (13 feet) at this location http://www.geerassociation.org/GEER_Post%20EQ%20Reports/Duzce_1999/kaynasli1.htm

  9. Reverse fault Pushes on the crust squeezing rock until it folds or breaks (like a trash compactor) = Occurs when plates are moving together compression Hanging wall Foot wall Results in hanging wall slipping upward animation

  10. What type of fault? reverse Hanging wall Foot wall http://geologicalintroduction.baffl.co.uk

  11. What type of fault? http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  12. Focus – 1. point inside the Earth where an earthquake begins – 2. point on Earth’s surface above focus where earthquake is FELT most strongly Epicenter 2 1

  13. How Seismographs Work A seismograph is an instrument used for recording the intensity and duration of an earthquake. the pendulum remains fixed as the ground moves beneath it http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  14. Earthquakes • How are earthquakes measured? Seismogram – seismic wave display record Seismograph machine

  15. Seismic Waves

  16. 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

  17. 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

  18. Comparing Seismic Waves

  19. Surface Waves • 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 Animation of wave types

  20. 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

  21. Typical Seismogram How much time elapsed between the arrival of the P wave (start) and the arrival of the S wave (finish)? finish start http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

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

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

  24. Now you are going to be seismologists and locate an Earthquake http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Go to: http://tinyurl.com/11quake13 Click here to go to virtual earthquake site

  25. National Geographic earthquake information

  26. How are Earthquakes Measured? Richter Scale A logarithmic scale used to express the total amount of energy released ___________ of an earthquake. Its values typically fall between 0 and 9, with each increase of 1 representing a _________ increase in energy. magnitude 10-fold

  27. How are Earthquakes Measured? Mercalli Intensity Scale A scale of earthquake intensity based on ___________ and ranging from I (detectable only with instruments) to XII (causing almost total destruction). observed effects Click for Interactive Demo Go to http://tinyurl.com/13quake13

  28. Earthquake Waves & Earth’s Interior Seismic wave animation

  29. Seismic Waves in the Earth Click here for animation http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  30. Tsunamis Click here for explanation of a tsunami http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

  31. Formation of a tsunami a large ocean wave usually caused by an underwater earthquake or a volcanic explosion. PBS –tsunami animation http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

  32. With typical waves, water flows in circles, but with a tsunami, water flows straight. This is why tsunamis cause so much damage! Click here for Japan helicopter view of tsunami

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

  34. Review Questions 1. A large ocean wave usually caused by an underwater earthquake or a volcanic explosion. tsunami 2. Used to describe both a sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip earthquake

  35. How are Earthquakes Measured? 3. Which one uses a logarithmic scale to express the total amount of energy released or magnitude of an earthquake. Richter Scale 4. Which uses a scale of earthquake intensity based on observed effects and ranging from I (detectable only with instruments) to XII (causing almost total destruction). Modified Mercalli Scale

  36. What type of fault is shown by each picture? 1. 2. Normal Reverse Transverse or strike-slip 3.

  37. Which type of wave travels through solids only? S-wave

  38. Which type of wave causes the most destruction? Surface or Love waves

  39. What type of fault? Source: indiana.edu B http://geologicalintroduction.baffl.co.uk A Strike –slip or transverse fault Hanging wall has moved upward Reverse fault

  40. Focus – 1. point inside the Earth where an earthquake begins – 2. point on Earth’s surface above focus where earthquake is FELT most strongly Epicenter 2 1

  41. People walk along a damaged road in the province of Bohol on Tuesday, October 15, 2013. Do you think this was a major earthquake? Why or why not?

  42. Yes, it was a major quake. It crumbled a number of buildings Such as this church 7.1 magnitude earthquake hit the Philippines

  43. Earthquakes 3. Surface 1. P-wave 2. S-wave Seismogram ____________ seismic wave display record 4. Seismograph 5. __________ machine

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