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  1. 1. Earthquake
  2. 2. <ul><li>Foci – location inside earth where an earthquake starts </li></ul><ul><li>Epicenter – Point on earth’s surface directly above the focus </li></ul>
  3. 3. Anatomy of Earthquakes
  4. 4. <ul><li>Amount of Damage is dependant on depth </li></ul><ul><li>Foci is close to surface – lots of damage </li></ul><ul><li>Foci is far from surface – little damage – energy has to travel a long way </li></ul>
  5. 5. Seismic waves – p 529 <ul><li>3 Types: P, S, and L </li></ul><ul><li>L waves – surface waves – roll along the earth’s surface </li></ul><ul><li>Body waves: P and S waves </li></ul><ul><li>Body waves travel faster than surface waves- feel p and s waves first after an earthquake </li></ul>
  6. 6. Body waves <ul><li>P wave- Primary wave -first to arrive </li></ul><ul><ul><li>Ground squeezes and streches in the direction of wave travel </li></ul></ul><ul><ul><li>Travels through solids and liquids </li></ul></ul><ul><li>S wave- secondary wave -second to arrive </li></ul><ul><ul><li>Ground is perpendicular (90) to direction of wave travel </li></ul></ul><ul><ul><li>Travels through solids but not liquids </li></ul></ul><ul><ul><li>Another name for S-wave is shear wave </li></ul></ul>
  7. 7. Smaller amplitude than surface (L) waves, but faster, P arrives first P and S waves
  8. 8. Two Types of Surface Waves Most of the destruction Larger amplitude than body waves
  9. 9. Why do P waves reach stations before S? <ul><li>Outer core is Liquid – S waves can’t travel through, but p can p 530 </li></ul>
  10. 10. Surface waves <ul><li>L wave – Travels along the earth’s surface </li></ul><ul><li>Last to arrive </li></ul><ul><li>Ground motion is a rolling action like ripples on a pond </li></ul>
  11. 11. Seismology <ul><li>Seismometers - instruments that record seismic waves </li></ul><ul><ul><ul><li>Records the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape </li></ul></ul></ul>
  12. 12. A seismograph designed to record vertical ground motion The heavy mass doesn’t move much The drum moves
  13. 13. Lateral Movement Detector In reality, copper wire coils move around magnets, generating current which is recorded.
  14. 14. <ul><li>Seismograms tell : </li></ul><ul><li>How long an earthquake lasted and the amount of ground shaking </li></ul><ul><li>Magnitude – rates the strength of an earthquake </li></ul><ul><li>Higher the magnitude the stronger the earthquake </li></ul>
  15. 15. <ul><li>Each 1 step increase in magnitude = 10 times the size of seismic waves </li></ul><ul><li>Seismograms determine how fast seismic waves are travelling. </li></ul><ul><li>Look at p531 </li></ul><ul><li>P waves = 5.5 min and S = 10 min </li></ul>
  16. 16. Earthquake focus and epicenter
  17. 17. Note how much bigger the surface waves are Body Waves Delay between P and S arrivals gives distance to epicenter
  18. 18. Graph to find distance to epicenter
  19. 19. <ul><li>Don’t need to know the next few slides, but it is cool to do ;) </li></ul>
  20. 20. <ul><li>Locating the epicenter of an earthquake </li></ul><ul><ul><ul><li>Three seismographs needed to locate an epicenter </li></ul></ul></ul><ul><ul><ul><li>Each station determines the time interval between the arrival of the first P wave and the first S wave at their location </li></ul></ul></ul><ul><ul><ul><li>A travel-time graph then determines each station’s distance to the epicenter </li></ul></ul></ul>
  21. 21. Locating Earthquake Epicenter
  22. 22. <ul><li>Locating the epicenter of an earthquake </li></ul><ul><ul><ul><li>A circle with radius equal to distance to the epicenter is drawn around each station </li></ul></ul></ul><ul><ul><ul><li>The point where all three circles intersect is the earthquake epicenter </li></ul></ul></ul>
  23. 23. Epicenter located using three seismographs
  24. 24. <ul><li>Earthquake Belts </li></ul><ul><li>95% of energy released by earthquakes originates in narrow zones that wind around the Earth </li></ul><ul><ul><ul><li>These zones mark of edges of tectonic plates </li></ul></ul></ul>
  25. 25. Locations of earthquakes from 1980 to 1990 Broad bands are subduction zone earthquakes, narrow are MOR 80% of seismic energy around Pacific Rim