1. Earthquakes

2. Vibration of earth produced by rapid release of energy (seismic waves) with radiate in all directions from the source (focus) Elastic Rebound Theory Explains how this works.

3. Like ripples from dropping a stone in a pond, energy dissipates with distance

4. Earthquakes don't occur randomly
Earthquakes don't occur randomly Occur on faults or fractures within the earth

5. Explained by plate tectonics.
Most occur on plate boundaries.
Sometimes in plate interiors
if enough stress is built up

6. Earthquakes Most destructive forces on Earth. But it is buildings
and other human structures that cause injury and
death, not the earthquake itself
Soviet Armenia: magnitude 6.9, 25,000 people died
Mexico City: magnitude 8.1, 9500 people
Loma Prieta, CA: magnitude 7.1, 40 people died
Kobe, Japan: magnitude 7, ~6000 people died

7. Soviet Armenia: 1988

8. Mexico City

9. Kobe, Japan 1995

10. Alaska 1964

11. 30,000 earthquakes occur worldwide annually that are strong enough to be felt, but typically only 75 of them are considered to be significant

12. Mechanism Elastic rebound theory Duration of Shaking Varies
Forces bend rock on either side of fault, rock strains ever so slowly, then weakest point breaks. Break sends out shock waves, which migrate outwards from the original break, causing shaking. Stress is released
Aftershocks are adjustments to that change in stress. They are always less strong than the main shock, but they may cause more damage to weakened structures.
Duration of Shaking Varies
1960 San Francisco: 40 seconds
1989 Loma Prieta: 15 seconds
1962 Alaska: 4 minutes!!!!

14. Earth material can either fold or fault when put under stress

15. If the Earth folds, it is said to be ductile.

16. If the Earth faults, it is said to be brittle.

17. Normal
Reverse

18. The following animations are types of faults in motion: Normal, Reverse/thrust, and Strike Slip

19. There are 2 types of Earthquake Waves: Body Waves and Surface Waves

20. Body Waves: Because they travel through the body of the earth.

21. Body Waves
P waves:
Pressure or compressional waves. Vibrate parallel to direction of wave travel like a slinky.
Fast travel: 4-7 km/sec (15,000 mph)
P is primary, or first wave to arrive at recording station

22. Body Waves
S waves:
Shear waves. Vibrates perpendicular to direction of wave travel. Like snapping a rope
Slower than P wave: 2-5 km/sec (11,000 mph)
So S is secondary, or second wave to arrive at recording station

23. Body Waves
S waves:
Shear waves. Vibrates perpendicular to direction of wave travel. Like snapping a rope
Slower than P wave: 2-5 km/sec (11,000 mph)
So S is secondary, or second wave to arrive at recording station

24. Earthquake waves in review

25. Examples of Body Waves on a Seismogram

26. Surface Waves: Because they travel along the surface of the Earth
Surface Waves: Because they travel along the surface of the Earth. These waves travel slower than Body Waves and are very destructive.

27. Love Waves: cause particles to move from side to side, perpendicular to direction of travel, similar to S wave.

28. Rayleigh Waves: travel more slowly than Love Waves and cause particles to move in elliptical patterns

29. Types of Waves
Earthquake waves = seismic waves. Recorded on seismometers on seismographs.
Types of Waves
Surface waves - travel on Earth's surface, away from epicenter.
Very slow waves. Cause a lot of damage, rolling feeling at end of earthquake
Body Waves - travel through Earth's interior, spread outward from focus

30. Earthquake waves in review

31. Seismogram Tracings

32. Locating the Epicenter of an Earthquake
P, S and surface waves all start out at same time.
The further you are away from the quake, the longer the time span between arrival of P and S wave.
The distance of the seismometer to the earthquake can be determined by the time between the arrival of P wave and arrival of S waves.
Can tell the distance, but not the direction.
Therefore, at least 3 sites must be used to find epicenter.

35. Studying Earth’s Interior

36. Travel of P and S Waves Through the Body of the Earth
How did geophysicists discover what was inside of our earth?

37. Travel of P and S Waves Through the Body of the Earth
They discovered that P waves will travel through solid and liquid, whereas S Waves will only travel through a solid.