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EARTHQUAKES

EARTHQUAKES. When good rock goes bad!. An Earthquake begins at the…. Focus: The point where the energy is released after elastic limit is reached. Epicenter: The point on the surface of the Earth directly above the focus. EARTHQUAKES.

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EARTHQUAKES

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  1. EARTHQUAKES When good rock goes bad!

  2. An Earthquake begins at the… • Focus: The point where the energy is released after elastic limit is reached. • Epicenter: The point on the surface of the Earth directly above the focus.

  3. EARTHQUAKES Shaking of the ground caused by sudden release of energy stored in rocks.

  4. STRESS! A force that acts upon a rock to change its shape or volume

  5. Stress Types Add compression… Compression - pushing together

  6. Stress Types Add tension… Tension - pulling apart

  7. Stress Types Add shearing… Shearing – pushing in opposite directions

  8. Fault Terminology

  9. Types of Faults Normal Fault – results from tensional stress, hanging wall moves down relative to foot wall

  10. Types of Faults Reverse Fault – results from compressional stress, hanging wall moves up relative to foot wall

  11. Types of Faults Strike-Slip Fault – results from shearing stress, rocks on either side of fault slip past each other sideways with little motion up or down

  12. Offset produced by 1906 San Francisco quake

  13. Focus and Epicenter

  14. Types of seismic waves: Primary Waves (P-Waves) Secondary Waves (S-Waves) Surface Waves (Love and Rayleigh)

  15. Primary Waves (P-Waves) • The fastest wave, they arrive 1st • Compressional motion in the wave (push-pull) • Vibration is parallel to the direction of wave propagation

  16. Primary (P) Waves: • Move out from the earthquake focus. • Travel the fastest of the 3 waves. • Travel twice as fast as secondary waves. • Move by causing particles in rocks to move back and forth in the same direction that the wave is traveling. • Example: slinky • Are bent and slowed when they hit the outer core. • Longitudinal wave Blue-

  17. Secondary Waves (S-Waves) Shear waves (side-side) Vibration is perpendicular to the direction of wave propagation

  18. Surface Waves Slowest and most destructive Rayleigh Waves: elliptical motion Love Waves: horizontal motion (perpendicular to travel)

  19. Secondary (S) Waves: • Move out from the earthquake focus. • Move slower than primary waves. • Move by causing particles in rocks to move at right angles to the direction of wave travel. • Example: rope • Cannot travel through liquids, so they are stopped by the outer core. • Transverse Wave Red-

  20. Surface Waves: • Form when P and S waves reach the surface. • Slowest Waves, Most destructive • Can cause the ground to shake making rock roll and sway from side to side. • Only travel through crust

  21. How are earthquakes detected? Seismographs

  22. Seismograph: • instrument used to record the energy released by an earthquake. Recording time of wave arrival. • Produces paper sheet called a seismogram • A stationary pen traces a record of vibrations

  23. Seismograph Stations • P waves arrive first • S waves arrive second • Surface waves arrive last (slowest) • 3 or more seismograph stations are needed to determine the location of the epicenter. • When an epicenter is far from a location, the p wave has more time to put distance between it and the s and surface waves.

  24. Reading a Seismogram

  25. Calculating lag time (oh no, more math!) To calculate lag time, simply subtract arrival time of S-wave from arrival time of P-wave. 7:14.2 7:17.4 P-wave arrival time S-wave arrival time S - P = 7:17.4 – 7:14.2 = 3.2 minutes

  26. 3:00 1:00 9:00 4:00 2:00 10:00 5:00 3:00 11:00 6:00 4:00 12:00 13:00 7:00 5:00 6:00 14:00 8:00 9:00 7:00 15:00 8:00 16:00 10:00 9:00 17:00 11:00 12:00 10:00 18:00 11:00 19:00 13:00 20:00 14:00 12:00 13:00 15:00 21:00

  27. 5:00 6:00 7:00 8:00 9:00 P wavearrival = S wavearrival = L wavearrival = Lag time =

  28. Finding the Epicenter

  29. Shadow Zone Animation • http://www.earthquake.gov/learning/animations/animation.php?flash_title=Shadow+Zone+Flash+Animation&flash_file=shadowzone&flash_width=220&flash_height=300

  30. How damage occurs in an earthquake SHAKING some areas shake more than others unconsolidated sediments landfill wetlands LIQUIFACTION water rises to Surface of sediments

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