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Geology 12

Geology 12. Presents. Chp 10 Earth’s Interior & Isostacy Chp 11 Ocean Floor Chp 12 Plate Tectonics Chp 9 Seismology EQ Chp 13 Structure. Chp 9 Seismology. Kobe burning. Not a safe place to be if an aftershock hits!!!.

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Geology 12

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  1. Geology 12 Presents

  2. Chp 10 Earth’s Interior & Isostacy • Chp 11 Ocean Floor • Chp 12 Plate Tectonics • Chp 9 Seismology EQ • Chp 13 Structure

  3. Chp 9 Seismology

  4. Kobe burning

  5. Not a safe place to be if an aftershock hits!!!

  6. Earthquake (EQ) is the vibration of the Earth caused by a sudden release of energy, usually the result of faulting • Aftershocks are small adjustment EQs that follow a major EQ • Smaller but still can cause considerable damage, especially in weakened structures • Can occur weeks afterwards

  7. Fault Creep • Movement along fault lines occur smoothly & gradually • Causes cracks in sidewalks, offset fences • Very localized & slow

  8. Elastic Rebound Theory 1. The plates are constantly moving, except along their edges. Due to friction between plates.

  9. 2. The plates are like large springs which deform (bend, fold) as the plates continue to move.

  10. The plates (“springs”) wind up until…. 3. The rocks break along the fault, and the plates snap back to their original shape releasing the spring energy in the form of seismic waves = EQ.

  11. Seismology: study of EQs • Seismograph: instrument that detects, records, and measures various vibrations produced by EQs (+atomic blasts, explosions, meteorite impacts, landslides, and cavern collapses).

  12. Seismic Waves: radiate outward in all directions. epicentre focus Fault plane

  13. Benioff Zone: zone of EQ foci dipping into mantle away from trench, resulting from subduction. x x x x x x x x x x x x x x x

  14. 2 Types of Seismic Waves 1. Body waves: travel through Earth 2. Surface waves: travel only along ground surface (like ocean waves). Surface waves Body waves EQ

  15. 1. Body Waves: • P-waves = primary waves • travel through everything (solids, liquids, gases) • fastest (1st waves to arrive at seismograph) • Travel 5km/sec b) S-waves = secondary waves • travel only through solids • Second wave to arrive at seismograph. • Travel at 3km/sec

  16. 2. Surface Waves: several kinds but two most important are: a) L-waves = Love waves • Travel like an S-wave, but motion is horizontal = side to side • Very damaging to buildings and foundations b) Rayleigh waves • Slower than L-waves • Travel like water in waves • Particles travel in elliptical patterns

  17. Rayleigh Wave Love Wave

  18. Hand out WS 9.1 Note Helper

  19. Typical Seismogram (record from seismograph) Surface waves Body waves Arrival of S-wave Know this!!! Arrival of L-wave Timing marks Arrival of P-wave Back-ground noise amplitude P=S time interval time

  20. Handout WS 9.15 note helper

  21. Locating an EQ • Determine the distance to epicentre using P-S time interval (time may be given instead) a) Measure the P-S time interval/lag Arrival of P-wave Arrival of S-wave 3:00 minutes 8 11 6 9 5 7 12 10

  22. b) use either: • Rickter scale nonogram on WS 9.1 side 2 • Time-distance graph

  23. 2. Using a circle compass: • a) open compass equal to distance to epicentre • b) put needle on seismogragh location and drawout circle 3. Repeat steps 1 & 2 for for atleast 3 seismographs 4. Where circles cross = epicentre “triangle of error”

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