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Earth Systems 3209. Reference: Chapters 4, 15, 16, 19; Appendix A & B. Unit: 4 The Forces Within Earth. Unit 4: Topic 4.4. Earthquake Scales. Focus on . . . comparing the two scales that can be used to measure earthquake intensity and magnitude.

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slide1

Earth Systems 3209

Reference:

Chapters 4, 15, 16, 19; Appendix A & B

Unit: 4The Forces Within Earth

slide2

Unit 4: Topic 4.4

Earthquake Scales

Focus on . . .

  • comparing the two scales that can be used to measure earthquake intensity and magnitude.
  • identifying in relation to the Richter scale, how wave amplitude and energy released changes for every increment of one on the Richter scale.
earthquake scales
Earthquake Scales
  • An earthquake is the vibration of earth caused by a rapid release of energy. Slippage along pre-existing faults and sudden movement within a subduction zone are commonly the cause of earthquakes.
  • Seismologist use two scales when classifying earthquakes.
      • Modified Mercalli Scale
      • Richter Scale

Text Reference:

Pages 451 - 455

mercalli scale
Mercalli Scale
  • Measures the Intensity of an earthquake on a roman numeral twelve (XII) point scale.
  • In 1902 G. Mercalli developed a fairly reliable intensity scale which assesses the damage to various types of structures at a specific location.
  • Note that earthquake intensity is determined by several factors including:1) Strength of earthquake2) Distance from epicenter3) Nature of surface materials4) Building design
mercalli scale1
Mercalli Scale
  • The Mercalli scale does not give a true indication of the actual strength of an earthquake because the amount of damage done to different places will largely depend on, the type of materials used and the degree of construction of buildings and structures.
richter scale
Richter Scale
  • Measures the Magnitude of an earthquake on a ten (10) point scale.
  • In 1935, Charles Richter introduced the concept of earthquake magnitude.
  • Richter magnitude is determined by measuring the largest amplitude (wave height) recorded on the seismogram.
  • Largest recorded earthquake at that time had a Richter magnitude equal to 8.6
richter scale1
Richter Scale
  • Richter magnitude can be expressed in two ways:
    • wave amplitude increases ten fold (10X).
    • energy released increases thirty fold (30X).
  • While it is correct to saythat for each increase of 1 in Richter Magnitude, there is a tenfold (10X) increase inamplitude (height) of the wave.
  • It is incorrect to say that each increase of 1 in Richter Magnituderepresents a tenfold (10X) increase in the size of the Earthquake.
  • A better measure of the size of an earthquake is the amount of energy released bythe earthquake.
richter scale2
Richter Scale
  • Wave Amplitude
  • increases ten-fold (10X) with each increase in Richter magnitude.
    • thus, a magnitude 7earthquake releases 10 times more amplitude than a magnitude 6 earthquake.
    • a magnitude 8earthquake measures10 x 10(or 100 times) more amplitude than a magnitude 6 earthquake. And so on …….
richter scale3
Richter Scale
  • Energy released
  • increases thirty-fold (30X) with each increase in Richter magnitude.
    • each increase in 1 in Richter Magnituderepresents a 30 fold increase in the energy released (size).
    • Thus, a magnitude 7earthquake releases 30 times more energy than a magnitude 6 earthquake.
    • A magnitude 8earthquake releases 30 x 30 (or 900 times) more energy than a magnitude 6 earthquake. And so on ….
sample problem
Sample Problem

In terms of magnitude, an earthquake measuring 7.2 on the Richter scale has a wave amplitude of how many times greater than an earthquake measuring 4.2 on the Richter scale?

Answer: Amplitude

4.2

5.2

6.2

7.2

slide13

Example 1:

How many times more energy is released in a 6.5 Richter magnitude earthquake than in one with a Richter magnitude of 4.5?

(A) 20 (B) 60

(C) 100 (D) 900

Which of the following measures an earthquake's intensity based on the observed effects on people and structures?

(A) Richter scale

(B) Modified Mercalli scale

(C) Centigrade scale

(D) Moment magnitude scale

slide14

Example 2:

An earthquake with a magnitude of 7.2 did not cause any buildings to collapse. How would this earthquake be rated on the Richter and Mercalli scales?

slide15

Example 3:

Based on the information below, which earthquake showed the greatest amplitude and by how much?

(A) Japan by 10 times

(B) Japan by 30 times

(C) Mexico by 10 times

(D) Mexico by 30 times

An earthquake in Japan registered 7.5 on the Richter scale and

another earthquake in Mexico measured 6.5.

slide16

Your Turn . . .

Take the time and complete the following questions . . .(Solutions to follow)

Question:

With every increasing number on the Ricter Scale, which describes the correct factor by which the energy released and amplitude (size) increases for a given earthquake?

slide17

Solutions . . .

Question:

With every increasing number on the Ricter Scale, which describes the correct factor by which the energy released and amplitude (size) increases for a given earthquake?

slide18

Summary . . .

Overview of Points covered:

Earthquakes are measured using two (2) scales:

Mercalli – measures Intensity.

Richter – measures Magnitude.

Earthquake Magnitude is measured in two ways:

Wave amplitude – increases 10X (fold)

Energy released – increases 30X (fold)