1. Earthquakes and the Earth’s Interior

2. Earth Science – Chapter 8.1
8.1 Vocabulary

3. earthquake
The vibration of the Earth produced by the rapid release of energy.

4. focus
The point within the Earth where the earthquake starts

5. epicenter
The location on the surface directly above the focus

6. fault
Fractures in the Earth where movement has occurred

7. elastic rebound
Deformation – rocks bend and build up stored potential energy
The explanation stating that when rocks are deformed, they break, releasing the stored potential energy that results kinetic energy in the form of vibrations of an earthquake.

8. foreshock
A small earthquake that often precedes a major earthquake

9. aftershock A small earthquake that follows the main earthquake
This can be the most devastating part of an earthquake because it shakes pre-damaged structures

10. Earth Science – Chapter 8.1
8.1 Notes

11. Earthquakes
Each year, more than 30,000 earthquakes occur worldwide that are strong enough to be felt.
Most earthquakes are minor tremors, and about 75/year are considered major earthquakes.

12. Earthquakes
Earthquakes – the vibration of the Earth produced by the rapid release of energy 
The point within (inside) the Earth where the earthquake starts is called the FOCUS.
The EPICENTER is the location on the surface directly above the focus.

13. Earthquakes
Earthquakes are usually associated with large fractures in the earth’s crust and mantle called FAULTS.
Faults – fractures in the earth where movement has occurred.

14. 3 Types of Faults

15. 3 Types of Faults Strike-slip fault
rock strata are displaced mainly in a horizontal direction, parallel to the line of the fault.
Shear Stress

16. 3 Types of Faults Normal Fault
hanging wall has moved downward relative to the footwall.
Tensional Stress

17. 3 Types of Faults Reverse Fault
hanging wall rises relative to the footwall
Compressional Stress

18. Elastic Rebound Hypothesis
The springing back of the rock into its original form is called “elastic rebound”
Rocks are deformed, then break, releasing stored energy.

19. Earthquakes Aftershocks smaller earthquakes after the main earthquake.
Foreshocks
small earthquakes that often come before a major earthquake.

20. Earth Science – Chapter 8.2
8.2 Vocabulary

21. seismograph
An instrument that records earthquake waves

22. seismogram
A record made by a seismograph

23. Seismic Waves
Wave motions produced by earthquakes

24. Body Waves
Waves that travel through the surface of the Earth

25. P wave
Earthquake wave that pushes and pulls rocks in the direction of the wave, also known as a compression wave.
Through solids and liquids

26. S wave
A seismic wave that shakes particles perpendicular to the direction the wave is traveling
Only through solids

27. Surface Waves Slowest of the waves moves up and down and side to side
Most destructive

28. Earth Science – Chapter 8.2
8.2 Notes

29. Measuring Earthquakes
The study of earthquake waves, or seismology, dates back almost 2000 years.
Seismographs – instruments that record earthquake waves.
Seismogram – modern seismographs that amplify and electronically record ground motion.

30. Earthquake Waves
The energy from an earthquake spreads outward as waves in all directions from the focus.
Seismograms show that two main types of seismic waves are produced by an earthquake – surface waves and body waves.

31. Earthquake Waves Body Waves
Waves that travel through the Earth’s interior
P waves – “push – pull” waves. The push (compress) and pull (expand) rocks in the direction the waves travel.
S waves – shake the particles at right angles to the direction of travel.

32. Earthquake Waves
A seismogram shows all three types of seismic waves – surface waves, P waves, and S waves.

33. Locating an Earthquake
The difference in velocities of P and S waves provides a way to locate the epicenter.

34. Locating an Earthquake
The winning car is always faster than the losing car. The P wave always wins the race, arriving ahead of the S wave. The longer the race, the greater the difference in arrival times of the P and S waves at the finish line (seismic station). The greater the interval measured on a seismogram between the arrival of the first P wave and the first S wave, the greater the distance to the earthquake source.

35. A B Earthquake Quiz Letter A represents the (focus or epicenter)?
2. Letter B represents the (focus or epicenter)?
3. Small earthquakes that occur after a main earthquake and are often the most destructive part of an earthquake are called _______.

36. Earthquake Quiz
4. Seismic body waves that can travel through both liquids and solids are called _______ waves.
5. List in order the arrival of the three types of seismic waves at a seismograph station.
6. How many seismograph stations are required to locate the epicenter of an earthquake?
7. When rocks are deformed, they break, releasing the stored energy, which in-turn causes and earthquake. This process is known as the _________ rebound hypothesis

37. 8. Label the three fault types and indicate what kind of stress is involved in each one.
A B C.
Fault types: strike-slip, reverse, normal
Stress types: compressional, sheer, tensional

38. A B Earthquake Quiz Letter A represents the (focus or epicenter)?
2. Letter B represents the (focus or epicenter)?
3. Small earthquakes that occur after a main earthquake and are often the most destructive part of an earthquake are called _aftershocks_.

39. Earthquake Quiz
4. Seismic body waves that can travel through both liquids and solids are called __P_ waves.
5. List in order the arrival of the three types of seismic waves at a seismograph station.
P-waves, S-waves, Surface waves
6. How many seismograph stations are required to locate the epicenter of an earthquake? 3
7. When rocks are deformed, they break, releasing the stored energy, which in-turn causes and earthquake. This process is known as the __elastic_ rebound hypothesis

40. 8. Label the three fault types and indicate what kind of stress is involved in each one.
A B C.
Reverse fault
Compressional stress
Normal fault
Tensional stress
Strike-slip fault
Sheer stress

41. Locating an Earthquake
Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter.

42. Locating an Earthquake
Earthquake Zones
95% of the major earthquakes occur in a few narrow zones
circum-Pacific belt: Japan, Philippines, Chile, and Alaska’s Aleutian Islands
Mediterranean – Asian belt

43. Most earthquakes occur at convergent plate boundaries

44. Ancient Chinese Seismograph
Earthquakes are a big problem in China, where there are many earthquakes, and often strong ones. Under the Han Dynasty, a man called Zhang Heng invented the first seismograph in the world - the first way to record an earthquake.
Zhang Heng's seismograph was a bronze jar about three feet across, with eight small dragons perched on it. Each dragon had a ball balanced in his mouth. When there was an earthquake, the closest dragon's mouth would open, letting the ball drop into the mouth of a waiting frog. This showed what direction the earthquake was coming from. Zhang Heng's seismograph could tell what direction an earthquake was coming from up to 500 kilometers (310 miles) away.

45. Measuring Earthquakes
Historically, scientists have used two different types of measurements to describe the size of an earthquake.
Intensity – measure of the amount of shaking at a given location based on damage
Magnitude – measure of the amount of energy released

46. Measuring Earthquakes
Richter Scale
Based on amplitude of largest seismic waves.
A 10x increase in wave amplitude equals an increase of 1 on the magnitude scale.
Example – a 5.0 magnitude is 10 times greater than a 4.0 magnitude

47. Measuring Earthquakes
Moment Magnitude
Amount of displacement that occurs along a fault zone.
Estimate the energy released by earthquakes.

49. Measuring Earthquakes
Modified Mercalli Scale
Rates an earthquake’s intensity in terms of the earthquake’s effects at different locations.
Example – Earthquake barely felt is a “I”
Earthquake that causes near/total damage is a “XII”

50. Seismic Vibrations
The damage to buildings and other structures from earthquake waves depends on several factors.
These factors include the intensity and duration of the vibrations, the nature of the material on which the structure is built, and the design of the structure.
Liquefaction - soils and other unconsolidated materials saturated with water are turned into a liquid that is not able to support buildings.

51. Tsunamis Tsunami – seismic sea wave
A tsunami triggered by an earthquake occurs where a slab of the ocean floor is displaced vertically along a fault.
A tsunami can also occur when the vibration of a quake sets an underwater landslide into motion.

52. Other Dangers
With many earthquakes, the greatest damage to structures is from landslides and ground subsidence, or the sinking of the ground triggered by vibrations.

53. Predicting Earthquakes
The goal of short-range prediction is to provide an early warning of the location and magnitude of a large earthquake.
So far, methods for short-range predictions of earthquakes have not been successful.
Long-range forecasts give the probability of a certain magnitude earthquake occurring within years.

54. Predicting Earthquakes
Scientists study historical records and look for seismic gaps (area of fault where no activity has taken place for a long time).
Scientists don’t yet understand enough about how and where earthquakes will occur to make accurate long-term predictions.

55. Fin

56. Ag Earth Science – Chapter 8.4
8.4 Vocabulary

57. crust
The thin, rocky outer layer of the Earth

58. mantle
The 2890 km – thick layer of earth located below the crust

59. lithosphere
The rigid outer layer of earth including the crust and upper mantle

60. asthenosphere
A weak plastic layer of the mantle situated below the lithosphere

61. outer core
A layer beneath the mantle about 2260 km thick

62. inner core
The solid innermost layer of the earth, about 1220 km in diameter

63. Moho
It is the boundary separating the crust from the mantle, discernable by an increase in the velocity of seismic waves

64. Layers Defined by Composition
Earth’s interior consists of three major zones defined by its chemical composition – the crust, mantle, and core.
Crust – the thin, rocky outer layer of Earth, is divided into oceanic and continental crust.
Mantle – 82%+ of the earth’s volume is contained in the mantle – a solid, rocky shell that extends to a depth of 2890 km.
Core – the core is a sphere composed of iron-nickel alloy

65. Layers Defined by Physical Properties
Earth can be divided into layers based on physical properties – the lithosphere, asthenosphere, outer core, and inner core.
Lithosphere – Earth’s outermost layer that is about 100 km in thickness. Consists of the crust and uppermost mantle.
Asthenosphere – lies beneath the lithosphere and is a softer, weaker layer due to it’s high temperature “waxy” texture.
The core is divided into the outer (liquid) core and inner (solid) core.

66. Discovering Earth’s Composition
Early seismic data and drilling technology indicate that the continental crust is mostly made of lighter, granitic rocks.
The crust of the ocean floor has a basaltic composition
Earth’s core is thought to be mainly dense iron and nickel, similar to metallic meteorites. The surrounding mantle is believed to be composed of rocks similar to stony meteorites.