1. How and Where Earthquakes Happen
Chapter 12-1
How and Where Earthquakes Happen

2. Earthquakes Movement of ground caused by a sudden release of energy
Movement along faults

6. Why Earthquakes Happen?
Rocks under stress suddenly shift along faults
Stress caused faults to break

7. Elastic Rebound
Return of elasticity from deformed rock to original shape
Rebound back into shape starting from weakest point

9. Earthquake Parts Focus – point of 1st motion of a quake
90% shallow
Epicenter – point on surface above the focus
Most damage

10. focus 0 km – 70 km are shallow 70km – 300 km are intermediate
Most damage. WHY?
70km – 300 km are intermediate
300 km – 650 km are deep

11. Seismic Waves Travel in all directions
Body wave – travel through the body of them medium
Surface wave – Travel on surface of material NOT through the middle
Vibrations are called seismic waves

12. Body Waves waves travel at different speeds
P wave – Primary or compression
Fastest
Move through solids, liquids, & gases
The more ridged the material the faster they move

13. Body Waves S wave – Secondary 2nd fastest Side to side motion
Only travel in solids

14. Surface Waves Shallow faults Slowest Cause Greatest Damage 2 types
Love – side to side
Rayleigh - rolling

15. Seismic Waves and the Interior
Useful in determining the Earth’s interior
Tells about the makeup and structure of earth

16. Boundaries located because of seismic waves
Crust
Mantle
Lithosphere
Mesosphere
Asthenosphere
core
Inner
outer

17. Reading check What causes the speed of a seismic wave to change???
As it passes through
Different layers of
Earth

18. Shadow Zones
Area where no direct seismic waves can be detected

19. Earthquakes and tectonic plates
Earthquakes are the result of stresses in the lithosphere
Most occur in 3 main tectonic environments

20. Convergent Ocean Environments plates moving together

21. Divergent Oceanic Environments plates moving apart

22. Continental Environments

23. Fault Zones Region of numerous faults
Faults zones form at plate boundaries b/c of intense stress as the plates move

24. Earthquakes Away from Faults
New Madrid, Missouri
1811 and 1812
Felt in South Carolina
Ancient fault deep in Earth
Buried by sediment

25. Studying earthquakes lesson 2
Seismology- study of earthquakes and seismic waves
Seismograph-detects and records vibrations
Vertical and horizontal motions recorded

26. First waves to detect
P- waves

27. Second waves to record
S-waves
Surface waves
Love
Rayleigh
Arrive last

28. Locating an earthquake
Scientist analyze the arrival times of the p & s waves
A longer lag time between p & s waves means the further away the EQ occurred.

29. Draw 3 circles~where they intersect is the location of the epicenter

30. Measuring EQ’s Magnitude- strength of ground motion
Richter scale- gives a strength reading

32. Intensity of EQ’s
Mercalli scale- effects of the earthquake

33. Earthquakes and society lesson 3
The movement of the ground isn’t what causes injury –it’s the collapsing building
Or other dangers
Fire
Down electric & gas
Explosion
Landslides
Etc.

34. tsunami
Earthquakes that occur in the water may cause tsunamis

35. EQ safety
If you live in an area where EQ’s occur you should be prepared

36. Earthquake 101

37. Seismic gaps Areas where few EQ’s occur~ but have occurred in the past
Where EQ are likely to occur in the future

38. foreshock Small earthquakes that precede EQ
Can be minutes before or weeks

39. Changes in rocks Looking for signals
Hoping to detect EQ’s early or before they happen
Water in cracks
Natural gas seepage
Magnetic properties

40. Forecasting EQ’s is not reliable
Scientists keep looking for ways to improve

41. Michigan Earthquakes May 2, 2015 in Battle Creek March 2015 in Portage
Earthquakes do
occur in Mi.