1. Inside Earth: Chapter 2- Earthquakes
Section 2: Measuring Earthquakes

2. Guide For Reading What are the different kinds of seismic waves?
How does the energy of an earthquake travel through Earth?
What are the scales used to measure the strength of an Earthquake?

3. There are about ______ earthquakes per day, worldwide.
8,000

4. Most earthquakes begin below the earth’s surface in the _______ within ______ kilometers from Earth’s surface.
Lithosphere
100

5. Focus
The point beneath Earth’s surface where rock breaks under stress and causes an earthquake

6. Epicenter
The point on Earth’s surface directly above an earthquake’s focus

7. Seismic Waves

8. Seismic Waves
A vibration that travels through Earth carrying the energy released during an earthquake

9. Figure 11: At what point do seismic waves first reach the surface?
The epicenter

10. What determines how much the ground shakes during an earthquake?
How close a location is to the epicenter
The types of rock and soil surrounding the epicenter determines how much the ground shakes

11. Guide For Reading: What are the different kinds of seismic waves?
There are three types of seismic waves:
Primary Waves (P waves)
Secondary Waves (S waves)
Surface Waves
An earthquake sends out two types of waves P waves and S waves
When the waves reach Earth’s surface at the epicenter, surface waves develop.

12. Primary Waves

13. Primary Waves (P Waves)
A type of seismic wave that compresses and expands the ground
The first wave to arrive at an earthquake

14. Describe how P waves move?
P waves compress and expand like an accordion
When P waves arrive they vibrate the particles of the crust forward and back along the path of the wave

15. Secondary Waves

16. Secondary Waves (S Waves)
A type of seismic wave that moves the ground up and down or side to side

17. How are P waves different from S Waves?
P waves compress and expand the ground
These waves cause buildings to contract and expand
P waves travel through solids and liquids
S waves vibrate from side to side
These waves vibrate from side to side and thrust the ground up and down, or back and forth
S waves can not move through liquids

18. Surface Waves

19. Surface Waves
A type of seismic wave that forms when P waves and S waves reach Earth’s surface

20. Why do you think surface waves produce more severe ground movements than P waves and S waves?
Surface waves consist of loose soil, sand, gravel, mud, small rocks, not solid rock
These more loose substances are more likely shift and slide

21. Guide For Reading: How does the energy of an earthquake travel through Earth?
Seismic waves carry the energy of an earthquake from the focus, through Earth’s interior, to the epicenter, and across the surface

22. Detecting Seismic Waves

23. Seismograph
A device that records ground movements caused by seismic waves as they move through Earth
Pg 156

24. Describe how a mechanical seismograph records ground movement. Pg 156
A heavy weight attaches to a frame by spring or wire
A pen connected to the weight rests its point on a rotating drum
During an earthquake the seismic waves cause the drum to shake while the pen stays in place
The pen records lines on the paper around the drum

25. Measuring Earthquakes

26. There are at least ______ different measures for rating earthquakes.20

27. Magnitude
The measurement of an earthquake’s strength based on seismic waves and movement along faults

28. The Mercalli Scale

29. Mercalli Scale
A scale that rates earthquakes according to their intensity and how much damage they cause
Developed in the early twentieth century

30. An earthquake’s ______ is the strength of ground movement in a given place.
Intensity

31. The Mercalli scale has ______ steps and describes how an earthquake affects ______, ______, and the ______. 12
People
Buildings
Land surface

32. Figure 14: How would you rate the damage to the Foligno city hall on the Mercalli scale? 157
The damage would probably rate VII - VIII

33. The Richter Scale

34. Richter Scale
A scale that rates seismic waves as measured by a particular type of mechanical seismograph

35. How does the Richter scale measure an earthquake?
The Richter scale measures seismic waves using a seismograph
Over time, mechanical seismographs were replaced by electronic seismographs

36. What is a strength of the Richter scale when measuring earthquakes
What is a strength of the Richter scale when measuring earthquakes? What is a weakness?
Strength: Provides accurate measurements for small, nearby earthquakes
Weakness: Does not measure larger and more distant earthquakes well

37. How are the Mercalli scale and the Richter scale similar
How are the Mercalli scale and the Richter scale similar? How are they different?
Both measure the strength of an earthquake
The Mercalli scale measures the strength in terms of extent people notice the earthquake and the amount of damage caused
The Richter scale measures the size of seismic waves

38. The Moment Magnitude Scale

39. Moment Magnitude Scale
A scale that rates earthquakes by estimating the total energy released by an earthquake

40. Why is the moment magnitude scale used today by geologists to measure earthquakes?
The moment magnitude scale determines the total energy released by an earthquake
This scale uses a electronic seismograph that can measure earthquakes that are big or small, and near or far
Geologist examine movement along the fault and the strength of broken rock
These two measurements give a more accurate measurement of an earthquake

41. On which scale would an earthquake’s strength vary from one place to another? Explain.
The Mercalli scale because the amount of shaking that people would feel and the damage to objects would be greater in a place closer to the earthquake’s epicenter

42. Checkpoint (Page 158):What are three scales for measuring earthquakes
Checkpoint (Page 158):What are three scales for measuring earthquakes? Explain what each one measures.
Mercalli Scale
Measures earthquakes on how much damage they cause
Richter Scale
Measures seismic waves using a seismograph
Measures small and nearby earthquakes
Moment Magnitude Scale
Looks at the total energy released
Measures large and distant earthquakes
Helps scientists predict how much fault movement there was

43. Locating the Epicenter

44. How do scientists calculate how far a location is from the epicenter of an earthquake?
Scientists calculate the difference between arrival times of the P waves and S waves
The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

45. Figure 17: Use the map scale to determine the distances from Savannah and Houston to the epicenter. Which one is closer? Pg 159
Houston
800 Km
Savannah
900 km