1. Earthquakes
Chapter 8 & Then Some

2. Where do Earthquakes occur?
Most earthquakes take place near the edges of tectonic plate.
Earthquakes occur along faults, where blocks of crust move.

3. Earthquake Zones
Earthquakes can occur near the Earth’s surface or far below the surface.
Most earthquakes occur at plate boundaries (in earthquake zones), but some happen at faults located in the middle of tectonic plates.

5. Earthquake Locations Around the World

6. What Causes Earthquakes?
Caused by movement along faults (breaks in the Earth’s surface)
Rock deforms (changes) due to stress
Two types of deformation:
Plastic deformation: bending of rock; no earthquakes created
Elastic deformation: bending of rock until it breaks; causes earthquakes

7. What is Elastic Rebound?
occurs when rock is suddenly returned to its undeformed (original) shape
Example: rubberband snapping back after being stretched
The rock will bend until enough force causes the rocks on either side of a fault to move and release energy.
Think of it as a rubber band being stretched to its limit and released—it snaps back.

8. Elastic Rebound

10. Earthquakes in Alabama?!
Surely, you’re kidding? How? Why?

11. The New Madrid Fault
If there is no plate boundary in the middle of the United States, why do these earthquakes take place?
Geologists are beginning to understand the answer. The New Madrid Fault Zone is part of an ancient plate boundary.
In this area, the North American Plate tried to form a divergent plate boundary about 500 million years ago. The splitting stopped before new plates could form.

12. The New Madrid Fault
The faults in the New Madrid Zone are remnants of this old event. Earthquakes occur because the North American Plate is still "settling down".
The faults in the New Madrid Zone do not reach the Earth’s surface.
They are buried beneath thousands of feet of rock and sediment deposited by the Mississippi River.
Geologists have located them by looking at the patterns of earthquakes in the zone.

13. New Madrid Fault
Several of the largest earthquakes ever recorded in the United States occurred in the Midwest, far from any plate boundary. These earthquakes took place in an area called the New Madrid Fault Zone, named after the town of New Madrid, Missouri.

14. New Madrid Fault
Over a three-month period in the winter of 1811 to 1812, the New Madrid Fault Zone was struck by three huge earthquakes estimated to be greater than magnitude 8.0 .
The New Madrid Fault is what causes Alabama to experience earthquakes.

15. Alabama’s Earthquake Zone

16. Alabama Earthquakes Since 1886

17. Earthquakes in Alabama
The last earthquake to occur in Alabama was on July 27, 2007.
It measured a 2.6 on the Richter scale.
(A little stronger than the one crazed LSU fans caused in October 9,1988, when they defeated Auburn 7-6 for the SEC title. 80,000 people jumping up & down created surface waves, triggering an earthquake. Imagine that many people jumping up & down on a trampoline.)
This was not a very strong earthquake, but it was recorded by a seismograph, an instrument used to measure earthquakes.

18. Earthquakes
Boundaries & Faults

19. 3 Types of Faults Associated with Earthquakes
PLATE MOTION
FAULT TYPE
Transform
Strike –Slip Fault
Convergent
Reverse Fault
Divergent
Normal Fault

20. Strike-Slip Fault occurs at a Transform Boundary

22. Reverse Fault occurs at a Convergent Boundary

24. Normal Faults occur at Divergent Boundaries

28. PLATE MOTION FAULT TYPE
Earthquakes and Faults Organizer: Draw the boundary on the plate motion side & the fault moving on the fault type side (label Hanging Wall & Foot Wall)
PLATE MOTION
FAULT TYPE
Transform Boundary: Plates move past each other
Strike –Slip Fault: Fault blocks move past each other
Convergent: Plates push toward each other
Reverse Fault: Fault blocks move toward each other
Divergent Boundary: Plates move apart
Normal Fault: Fault blocks move apart

29. Earthquake Energy: Just How Strong Was It Anyway?
Earthquake Energy=Seismic Energy

30. How do Earthquake Waves Travel?
Energy released from moving plates & faults travels through the Earth as waves.
Waves travel at different speeds & in different ways, depending on what kind of material they are moving through.

31. Earthquake Energy
This energy is called seismic energy and is measured in seismic waves:
Two types of seismic waves:
body waves
surface waves

32. Body Waves: waves that travel through the Earth’s interior
There are two types of body waves:
P-waves
S-waves

33. P and S wave comparison

34. P-waves: primary waves or pressure waves
travel through solid, liquids and gases
fastest waves (travel 5-8 km/h), arrive first & are first ones to be detected
P-waves cause rock to squeeze and stretch. Imagine a slinky!

35. P-Waves

36. S-waves: secondary waves
second fastest waves; 2nd to arrive; shear waves
slower than P-waves; travel 3-5 km/h
S-waves move rock from side to side.
S-waves can’t travel through parts of the Earth that are completely liquid.

37. S-Waves

38. Surface Waves move along the surface of the Earth
can move up, down & around or side to side
Surface waves move the slowest & cause the most destruction.
Think about it? Where do most people live: on the Earth’s crust or in it? Shouldn’t these waves be the most destructive since they occur where there is more stuff to destroy?

40. Surface Waves

41. Seismic Wave Arrival First- P-waves Second- S-waves
Third- Surface Waves

42. The area of the Earth that does not receive seismic energy is called the Shadow Zone.

43. Shadow Zone
The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.

44. Mohorovicic discontinuity: The Moho Zone
The Moho is the boundary between the crust and the mantle in the earth. This is a depth where seismic waves change velocity, or speed. They usually increase at this location—the Moho zone.
The Moho is the boundary between the crust and the mantle in the earth. This is a depth where seismic waves change velocity and there is also a change in chemical composition. Also termed the Mohorovicic' discontinuity after the Croatian seismologist Andrija Mohorovicic' ( ) who discovered it. The boundary is between 25 and 60 km deep beneath the continents and between 5 and 8 km deep beneath the ocean floor.

45. Quiz 1. Most Earthquakes occur along ________________.
2. The first seismic waves to arrive are______________.
3. The second seismic waves to arrive are _____________.
4. The last seismic waves to arrive are_______________.
5. Which seismic waves travel the fastest?___________
6. Which type of seismic wave can move through a solid, liquid or a gas?________________
7. Which seismic wave cannot travel through material that is completely liquid?______________
8. Which seismic waves are the slowest and the most destructive?_______________

46. Measuring Earthquakes
Seismographs & Seismograms
Wait aren’t those the same?

47. Measuring Earthquakes
Seismographs: instruments used to sense earthquakes
seismogram: tracing of earthquake movement made by seismograph
Seismologists use seismograms to locate earthquakes.

48. Picture of a Seismograph

49. Time and Location of Earthquakes
Seismologists use seismograms to find the epicenter of earthquakes:
the point on top of the Earth above the true center of an earthquake which is called the focus—it’s inside the Earth. (Also called the hypocenter.)

50. Seismograms

51. Measuring Earthquakes
Earthquakes are defined by their strength and depth, which is measured at the place the earthquake occurs.
2 Scales are used to rank the quakes:
Richter Scale—measures magnitude
Mercalli Scale—measures intensity

52. Earthquake strength & intensity
Richter scale: measures magnitude (think strength) of ground motion on a scale of (numbers)
Mercalli scale: measures degree to which an earthquake is felt by people & amount of damage caused, which is known as intensity
Scale of I-XII (Roman Numerals)

53. Magnitude
Effects
2.0
(2-2.9 very minor)
Only felt by seismograph
3.0
(3-3.9, minor)
Felt at epicenter
4.0
(4-4.9 light)
Felt by most people in area
5.0
(5-5.9, moderate)
Damage at epicenter
6.0
(6-6.9, strong)
Widespread damage
7.0
(7-7.9 major)
Great, widespread damage
8.0 or higher
(8 & up, great)
Catastrophic destruction

55. Reading Richter Scale Maps

56. Reading Mercalli Scale Maps

59. Seismograph
A seismograph is an instrument used by scientists to measure earthquakes.
Seismologists who study earthquakes can determine when an earthquake started by noting the arrival times of P-waves and S-waves.
A seismograph records vibrations in the Earth and determines the strength and location of an earthquake.

60. Chinese Seismograph
Ancient Chinese Seismograph. The ball would drop from the dragon to the frog. It told the people from which direction the earthquake came.

61. Seismograms 1. How many minutes did it take for the P-Waves to arrive?
Time in Minutes
1. How many minutes did it take for the
P-Waves to arrive?
2. How many minutes did it take for the
S-waves to arrive?
3. How long did the surface waves last?

62. Oahu IV
Maui V-VI
Hawaii
6.7
VII VI V

63. Questions from the Hawaii intensity map:
1. What was the magnitude of the Hawaii earthquake?
2. Where was the intensity the greatest?
3.According to the Mercalli Scale on what island did the most damage likely occur?

64. Mercalli Intensity Scale
What is the intensity at Monterey?
What is the intensity at the epicenter?
What is the intensity at San Jose?
What is the intensity at Santa Cruz?
What is the intensity at Smith?
Smith