Scientists measure the magnitude of an earthquake using the Richter scale, which quantifies the amount of energy released by the earthquake based on the amplitude of seismic waves recorded by seismographs. The larger the amplitude, the higher the magnitude.

1. 4.2 Recording Earthquakes
Mr. Silva

2. 4.2 Vocabulary

3. 4.2 Vocabulary
• Seismograph-
– instrument used to detect and record seismic
directions

4. 4.2 Vocabulary
• Seismograph-
– instrument used to detect and record seismic
directions
• P Waves-
– primary wave: the fastest wave generated by an
earthquake and the first to be recorded by a
seismograph.

5. 4.2 Vocabulary
• Seismograph-
– instrument used to detect and record seismic
directions
• P Waves-
– primary wave: the fastest wave generated by an
earthquake and the first to be recorded by a
seismograph.
• S Waves-
– secondary wave; a wave generated by an
earthquake and the second to be record by a
seismograph

6. 4.2 Vocabulary
• Seismograph-
– instrument used to detect and record seismic
directions
• P Waves-
– primary wave: the fastest wave generated by an
earthquake and the first to be recorded by a
seismograph.
• S Waves-
– secondary wave; a wave generated by an
earthquake and the second to be record by a
seismograph
• Surface Waves-

7. 4.2 Vocabulary
• Seismograph-
– instrument used to detect and record seismic
directions
• P Waves-
– primary wave: the fastest wave generated by an
earthquake and the first to be recorded by a
seismograph.
• S Waves-
– secondary wave; a wave generated by an
earthquake and the second to be record by a
seismograph
• Surface Waves-
– the slowest moving seismic wave generated by an
earthquake and the last to be recorded.

8. 4.2 Vocabulary

9. 4.2 Vocabulary
• Magnitude-

10. 4.2 Vocabulary
• Magnitude-
– Is a measure of the energy released by an
earthquake and is also described as the amount of
ground motion.

11. 4.2 Vocabulary
• Magnitude-
– Is a measure of the energy released by an
earthquake and is also described as the amount of
ground motion.
• Microquakes-

12. 4.2 Vocabulary
• Magnitude-
– Is a measure of the energy released by an
earthquake and is also described as the amount of
ground motion.
• Microquakes-
– earthquake with a magnitude less than 2.5 on the
Richter scale

13. 4.2 Vocabulary
• Magnitude-
– Is a measure of the energy released by an
earthquake and is also described as the amount of
ground motion.
• Microquakes-
– earthquake with a magnitude less than 2.5 on the
Richter scale
• Mercalli scale-

14. 4.2 Vocabulary
• Magnitude-
– Is a measure of the energy released by an
earthquake and is also described as the amount of
ground motion.
• Microquakes-
– earthquake with a magnitude less than 2.5 on the
Richter scale
• Mercalli scale-
– scale that expresses the intensity of an
earthquake with a Roman numeral and a
description.

15. 4.2 Vocabulary
• Magnitude-
– Is a measure of the energy released by an
earthquake and is also described as the amount of
ground motion.
• Microquakes-
– earthquake with a magnitude less than 2.5 on the
Richter scale
• Mercalli scale-
– scale that expresses the intensity of an
earthquake with a Roman numeral and a
description.
• Intensity-

16. 4.2 Vocabulary
• Magnitude-
– Is a measure of the energy released by an
earthquake and is also described as the amount of
ground motion.
• Microquakes-
– earthquake with a magnitude less than 2.5 on the
Richter scale
• Mercalli scale-
– scale that expresses the intensity of an
earthquake with a Roman numeral and a
description.
• Intensity-
– amount of damage caused by an earthquake.

17. Types of Seismic Waves
• Seismic waves can be detected and recorded
using a seismograph.
• There are 3 types of seismic waves
– Primary Waves (P waves)
– Secondary Waves (S waves)
– Surface Waves: (when P & S waves reach the
surface)

18. Primary Waves
– Primary Waves (P waves): move fastest
and are recorded first
• Can travel through solid & liquid
• Compression waves- cause the rock particles
to move together & apart along the wave
direction

19. Secondary Waves
– Secondary Waves (S waves): second to
be recorded
• Travel only through solid material: cannot be
detected on the side of the earth opposite the
epicenter…Why? Can’t go through the liquid of
the earth’s outer core!
• Shear waves- cause rock particles to move at
right angles to the wave direction

20. Surface Waves

21. Surface Waves
• Surface Waves: when P & S waves
reach the surface and their energy is
converted into a new wave

22. Surface Waves
• Surface Waves: when P & S waves
reach the surface and their energy is
converted into a new wave
– Slowest moving & last recorded

23. Surface Waves
• Surface Waves: when P & S waves
reach the surface and their energy is
converted into a new wave
– Slowest moving & last recorded

24. Surface Waves
• Surface Waves: when P & S waves
reach the surface and their energy is
converted into a new wave
– Slowest moving & last recorded
– Why do surface waves do the most
damage?

25. Surface Waves
• Surface Waves: when P & S waves
reach the surface and their energy is
converted into a new wave
– Slowest moving & last recorded
– Why do surface waves do the most
damage?

26. Surface Waves
• Surface Waves: when P & S waves
reach the surface and their energy is
converted into a new wave
– Slowest moving & last recorded
– Why do surface waves do the most
damage?
– Not as much earth to absorb energy
before hitting the surface

27. Locating an Earthquake

28. Locating an Earthquake
a. To find the epicenter, analyze the
difference between arrival times of P
& S waves

29. Locating an Earthquake
a. To find the epicenter, analyze the
difference between arrival times of P
& S waves
i. P waves travel 1.7 times faster than S waves

30. Locating an Earthquake
a. To find the epicenter, analyze the
difference between arrival times of P
& S waves
i. P waves travel 1.7 times faster than S waves
ii. The longer S waves take to come in, the
farther the seismograph station is from the
epicenter

31. Locating an Earthquake
a. To find the epicenter, analyze the
difference between arrival times of P
& S waves
i. P waves travel 1.7 times faster than S waves
ii. The longer S waves take to come in, the
farther the seismograph station is from the
epicenter
iii. Plot epicenter distances from 3 stations and
the intersection point is the earthquake
epicenter

32. Earthquake Measurement

33. Earthquake Measurement
– Magnitude a measurement of the energy
released by an earthquake & is the amount
of “ground motion”

34. Earthquake Measurement
– Magnitude a measurement of the energy
released by an earthquake & is the amount
of “ground motion”
i. Major quake = 7 or above

35. Earthquake Measurement
– Magnitude a measurement of the energy
released by an earthquake & is the amount
of “ground motion”
i. Major quake = 7 or above
ii. Moderate quake = 6 to 7

36. Earthquake Measurement
– Magnitude a measurement of the energy
released by an earthquake & is the amount
of “ground motion”
i. Major quake = 7 or above
ii. Moderate quake = 6 to 7
iii. Minor quake = 2.5 to 6

37. Earthquake Measurement
– Magnitude a measurement of the energy
released by an earthquake & is the amount
of “ground motion”
i. Major quake = 7 or above
ii. Moderate quake = 6 to 7
iii. Minor quake = 2.5 to 6
– Largest quake ever had a magnitude of 8.9

38. Earthquake Measurement
– Magnitude a measurement of the energy
released by an earthquake & is the amount
of “ground motion”
i. Major quake = 7 or above
ii. Moderate quake = 6 to 7
iii. Minor quake = 2.5 to 6
– Largest quake ever had a magnitude of 8.9
– Anything less than a 2.4 is a microquake.

39. Earthquake Measurement
– Magnitude a measurement of the energy
released by an earthquake & is the amount
of “ground motion”
i. Major quake = 7 or above
ii. Moderate quake = 6 to 7
iii. Minor quake = 2.5 to 6
– Largest quake ever had a magnitude of 8.9
– Anything less than a 2.4 is a microquake.
– Mercalli scale expresses intensity (damage
caused) in Roman Numerals I to XII

40. 4.2 Review

41. 4.2 Review
• What instrument is used to record seismic waves?

42. 4.2 Review
• What instrument is used to record seismic waves?
– Seismograph

43. 4.2 Review
• What instrument is used to record seismic waves?
– Seismograph
• Explain the three types of seismic waves…

44. 4.2 Review
• What instrument is used to record seismic waves?
– Seismograph
• Explain the three types of seismic waves…
– P (primary) moves the fastest through solids and
liquids.

45. 4.2 Review
• What instrument is used to record seismic waves?
– Seismograph
• Explain the three types of seismic waves…
– P (primary) moves the fastest through solids and
liquids.
– S (secondary) travel only through solids

46. 4.2 Review
• What instrument is used to record seismic waves?
– Seismograph
• Explain the three types of seismic waves…
– P (primary) moves the fastest through solids and
liquids.
– S (secondary) travel only through solids
– Surface Wave- Slowest wave, moves over the surface
causing the surface to rise and fall.

47. Review

48. Review
• How do scientists measure the magnitude of an
earthquake?

49. Review
• How do scientists measure the magnitude of an
earthquake?
– By analyzing and plotting the differences in arrival
times of P waves and S waves at three or more
seismograph station locations

50. Review
• How do scientists measure the magnitude of an
earthquake?
– By analyzing and plotting the differences in arrival
times of P waves and S waves at three or more
seismograph station locations
• Why do P waves travel faster through the
lithosphere than through the asthenosphere?

51. Review
• How do scientists measure the magnitude of an
earthquake?
– By analyzing and plotting the differences in arrival
times of P waves and S waves at three or more
seismograph station locations
• Why do P waves travel faster through the
lithosphere than through the asthenosphere?
– Because P waves travel faster through the more rigid
rock of the lithosphere than through the somewhat
plastic rock in the asthenosphere.