1. Earthquakes
Shake, Rattle, and Roll!

2. Lesson 7
Forces and Faults

3. What causes earthquakes?
Focus Question…
What causes earthquakes?
Where are they located?

4. A. Stress and Strain… What are earthquakes?
natural vibrations of the ground caused by movement along gigantic fractures in (Earth’s) crust

5. Stress and Strain… 1. When do most earthquakes occur?
when rocks fracture (break) deep within Earth
2. When do fractures form?
when stress exceeds the strength of the rocks involved

6. Stress and Strain… … the forces per unit area acting on a material
Stress and Strain…
3. What is stress?
… the forces per unit area acting on a material
… There are three types of stress…

7. Stress
Compression (squeezed material) decreases the volume of a material – occurs at convergent boundaries (& reverse faults)

8. Stress!
Tension (stretched material) pulls a material apart – at divergent boundaries (& normal faults)

9. http://rpmedia. ask. com/ts
Stress!
Shear (twisted material)causes a material to twist – at transform boundaries (& strike-slip faults).

10. Strain! the deformation of materials in response to stress
5. What is strain?
the deformation of materials in response to stress
It is represented by the solid line on your diagrams.

11. Elastic Limit 6. A slab of rock’s elastic limit is…
… the point at which it will undergo permanent deformation
7. Failure is…
… when material breaks!
We call this failure and earthquake!

12. Faults…
Rocks will fail and form a fault…when stress is applied too quickly or when stress is great
A fault is the resulting fracture (or system of fractures) along which movement occurs.

13. Reverse Fault… Is caused by… Movement of crust…
compression
Movement of crust…
block above fault moves up and over
convergent boundary

14. Reverse Fault – The Himalayas!

15. Normal Fault… Is caused by… tension (at a divergent boundary)
Normal Fault…
Is caused by…
tension (at a divergent boundary)
Movement of crust…
block above fault moves down
Divergent boundary)

16. Normal Fault – The Sierra Nevadas

17. Strike-slip Fault… Is caused by… horizontal shear Movement of crust…
Strike-slip Fault…
Is caused by…
horizontal shear
Movement of crust…
blocks slide past each other
horizontal (no vertical movement)
Transform boundary

18. The San Andreas Fault…

19. Draw and label these Faults Define “Fault” in your own words

20. Seismic Waves and Earth’s Interior
Lesson 8
Seismic Waves and Earth’s Interior

21. What are seismic waves and what can we learn from a travel-time graph?
Focus Question…
What are seismic waves and what can we learn from a travel-time graph?
Seismograph explanation

22. The Focus of an Earthquake…
The focus of an earthquake is where rocks break beneath (Earth’s) surface.
The epicenter is the location on Earth’s surface just above the focus.

23. Depth of Focus… The depth of an EQ’s focus
Another factor that determines the intensity of an earthquake is…
The depth of an EQ’s focus
Shallow-focus events will produce catastrophic quakes with high intensity values. (closer to the dynamite!)

24. Earthquake Waves… vibrations of the ground during an earthquake
Earthquake Waves…
1. What are seismic waves?
vibrations of the ground during an earthquake
“seismo-” means shaking!

25. Earthquake Waves…
2. How do the following types of seismic waves move rocks?
Primary (P) waves – squeeze (push) & pull rocks in the same direction as the wave

26. Earthquake Waves…
2. How do the following types of seismic waves move rocks?
b. Secondary (S) waves – cause rocks to move at right angles to direction of the wave

27. Earthquake Waves… Seismic Wave Rap!
c. Surface waves – move in 2 directions – up and down and side to side (slowest and most damaging!)
Seismic Wave Rap!

28. Seismic Waves and a Seismogram…
“So which wiggles are the earthquake? The P wave will be the first wiggle that is bigger than the rest of the little ones (the microseisms). Because P waves are the fastest seismic waves, they will usually be the first ones that your seismograph records. The next set of seismic waves on your seismogram will be the S waves. These are usually bigger than the P waves.
The surface waves are the other, often larger, waves marked on the seismogram. Surface waves travel a little slower than S waves (which, in turn, are slower than P waves) so they tend to arrive at the seismograph just after the S waves.”

29. Travel-Time Graph (not time travel!)
1. A travel-time graph is …
shows average travel time of P & S waves
This graph is used to calculate…
the distance to the epicenter (using the difference in arrival times of the p and s waves)

30. Travel-Time Curves
Suppose the waves recorded on a seismogram at Station A are farther apart than they are at Station B…
The epicenter is farther from Station A.
Animation for Lab 8 on next slide 

31. F. Clues to Earth’s Interior
1. Where does the knowledge of Earth’s interior come from?
The study of seismic waves
2. How do P-waves and S-waves move through the mantle?
They follow fairly direct paths
3. What do P-waves do when they strike the core?
They bend
4. Why don’t S-waves enter Earth’s core?
They cannot travel through liquids

32. Clues to Earth’s Interior
5. What does the disappearance of S-waves tell us about Earth’s outer core?
That it must be liquid
6. What shows us that Earth’s inner core is solid?
Studies of how P waves are deflected deep within Earth

33. Measuring and Locating Earthquakes
Lesson 9
Measuring and Locating Earthquakes

34. What is the strongest earthquake that has happened in your lifetime?
Think About It…
What is the strongest earthquake that has happened in your lifetime?
When was the last earthquake in NC?
Murphy NC

35. How are earthquakes measured and located?
Focus Question…
How are earthquakes measured and located?

36. Earthquake Magnitude and Intensity
How is the amount of energy released by an earthquake measured?
by its magnitude
Haiti, 1/2010 (7)

37. 1. The Richter Scale… An 8 is 10 times bigger than a 7
The Richter scale is based on…
size of the largest seismic waves generated by the quake (EQ)
Each successive number on this scale represents…
a 10 times increase in wave size
An 8 is 10 times bigger than a 7
An 8 is 100 times bigger than a 6

38. 1. The Richter Scale… Each increase in magnitude corresponds to…
A 32-times increase in seismic energy
An 8 releases 32 times more energy than a 7
An 9 releases 1024 times more energy than a 7
Bill Nye Richter scale

39. The Richter Scale Haiti, 1/2010 (7) Japan, 3/2011 (9)

40. 2. The Modified Mercalli Scale…
The intensity of an earthquake can be determined by…
amount of damage done to the structures involved (intensity)
The modified Mercalli scale is used to determine the intensity of an EQ by…
rate damage & other effects as noted by observers
This scale uses Roman numerals from I to XII. It was developed by Giuseppe Mercalli in 1902.

41. Modified Mercalli Scale… Did you feel it? usgs.gov

42. Modified Mercalli Scale…
d. A seismic intensity map is made by…
… compile MMsI values (Modified Mercalli scale intensity values), plot on a map, & join points of similar intensity.
Mercalli values at distances very far from the epicenter…
Decrease to I

43. Seismic Intensity Map… Northridge, California Earthquake

44. Look at the text page Where do most earthquakes occur in California?
Intensity Map of the Northridge Earthquake.

45. Locating an Earthquake…
The distance to an earthquake’s epicenter is determined by…
the time difference b/tw the arrival of the P-wave & the S-wave
This distance is called…
Epicentral distance
Three seismograph stations are needed to determine an EQ’s epicenter.

46. Locating an Earthquake…
3. Three seismograph stations are needed to determine an EQ’s epicenter.
5. A travel-time graph determines the exact time of an EQ.

47. Seismic Belts… 80% of earthquakes occur in…
Most earthquakes are associated with…
Tectonic plate boundaries
80% of earthquakes occur in…
The Circum-Pacific Belt
Another 15% of earthquakes occur at the
Mediterranean-Asian Belt
Most of the remaining earthquakes occur at
mid-ocean ridges

48. Lesson 10
Earthquake Hazards

49. Think About It…
Why do developing countries such as Haiti suffer such devastation from earthquakes?

50. How do earthquakes affect the four spheres of Earth?
Focus Question…
How do earthquakes affect the four spheres of Earth?
What are the 4 spheres again?

51. Structural Failure…
1. The types of buildings that sustain the most severe damage from earthquakes are…
Unreinforced, made of stone, concrete, or other brittle materials
Typical building in Iraq
Church, Armenia, 1988

52. Structural Failure…
2. The types of buildings that sustain the least amount of damage from earthquakes are…
wooden
high-rise, steel-framed
Kobe, Japan 1995

53. Structural Failure…
Pancaking is…
supporting walls of ground floor collapse causing upper floors to collapse
Pancaked Building in Turkey

54. Structural Failure…
4. Building with 5-15 stories may collapse because…
their natural sway has the same vibration period of an EQ
EQ Proof Building – Futures Channel

55. Land and Soil Failure… landslides!
5. Earthquakes in sloping areas can trigger…
landslides!
El Salvador, 2001, mag 7.6

56. Land and Soil Failure
6. Soil liquefaction
subsurface materials liquefy & behave like quicksand due to EQ vibrations

57. Land and Soil Failure… It is built on soft sediments.
7. Soft materials have no resistance to deformation.
There was much damage to structures in the Mexico City EQ of 1985 b/c...
It is built on soft sediments.

58. Fault Scarps… waterfall
8. A fault scarp is…
area of vertical offset where the fault intersects Earth’s surface.
9. The fault scarp shown created a…
waterfall

59. Tsunami strikes Ao Nang, Thailand
10. A tsunami is caused by…
vertical motion of seafloor (during the EQ) bumps the water over the fault
11. A tsunami in the open ocean is usually…
1 meter high (3 ft)
You wouldn’t notice it if you were there!

60. Tsunamis…
Sri Lanka, 2004
12. A tsunami is dangerous when it enters shallow water because…
it moves very fast
it can be very high – up to 30m (90 ft.)!

61. Tsunamis… 13. A recent devastating tsunami was in… Japan, March 2011
Youtube Clip:
13. A recent devastating tsunami was in…
Japan, March 2011

62. Seismic Risk… 14a. Five states with the greatest seismic risk… Alaska
California
Hawaii
Utah
Nevada
b. The San Andreas
Fault is a
transform boundary.

63. Seismic Risk… moderate
14c. The seismic risk of the NC Piedmont and mountains…
moderate
14d. The seismic risk of the coastal plains of NC…
low

64. Earthquake Prediction…
15. Earthquake recurrence rates indicate …
Where EQs happen repeatedly at regular intervals (generate similar quakes)

65. Earthquake Prediction…
Earthquake Prediction…
16. Seismic gaps are
sections of active faults that haven’t had EQs for a while
An earthquake is likely to happen here!
The San Andreas Fault

66. Earthquake Prediction…
17. Why is earthquake prediction important?
… to save lives and prevent property damage!!
San Andreas Fault

67. G. Earth’s Internal Structure…
Crust of lithosphere – granite (continental crust), basalt (oceanic crust)
Upper mantle – peridotite (intrusive, bumpy, igneous)
Asthenosphere – peridotite
Lower mantle – oxides of iron, silicon, and magnesium
Core – iron and nickel (magnetic field is generated here!