Types and Magnitudes of Earthquakes

Overview

This lesson is intended to help students learn about how earthquakes are measured, and the difference of varying intensities. Students will make associations between the modified Mercalli intensity scale and the Richter magnitude scale.

Estimated Time

Two class periods depending on what you choose to emphasize.

Materials

  • Growth Worksheet
  • Find that Earthquake Worksheet
  • Compasses
  • Pencils
  • Rulers

Objectives

Students will understand the differences between the Mercalli and Richter scales, and the use of each.

National Standards Addressed

Math (Presented by National Council of Teachers of Mathematics in 2000)
Numbers & operations
  • Understand numbers, ways of representing numbers, relationships among numbers, and number systems.
Algebra
  • Understand patterns, relations, and functions.
Geometry
  • Use visualization, spatial reasoning, and geometric modeling to solve problems.
Problem solving
  • Solve problems that arise in mathematics and in other contexts.
Connections
  • Recognize and apply mathematics in contexts outside of mathematics.
Representations
  • Use representations to model and interpret physical, social, and mathematical phenomena.
Science (Presented by National Research Council in 1996)
Physical science
  • Motions and forces
Earth & space science
  • Structure of the earth system
  • Earth’s history
Science in personal and social perspectives
  • Natural hazards
  • Risks and benefits
Technology (Presented by the International Society for Technology in Education in 1998)
Social, ethical, & human issues
  • Students understand the ethical, cultural, and societal issues related to technology.
Technoloy research tools
  • Students use technology to locate, evaluate, and collect information from a variety of sources.

Engagement Activity (optional)

On the first page of the worksheet have students figure out how tall a skyscraper would be if it were 10 times taller than the five-story apartment building. If the skyscraper is 10 times taller than the apartment building, and the apartment building is 10 times taller than the person, how much taller than the person is the skyscraper? On the second page of the worksheet students are asked to figure out the salaries of two of their friends in comparison to their own, see the relation of someone’s salary being 10 times more than their own, and 100 times more than their own.

Instructional Plan

Explain that earthquake damage involves many topics, three of which are:

  • The type of earthquake
  • The severity of the earthquake (magnitude and intensity)
  • The location of the earthquake.

In another lesson we will discuss another aspect involved in earthquake damage—structure of area.

Part One: Types of Earthquakes

Using the animation available on the following website, discuss with students the three types of plate boundaries described in the table 1.

Table 1
Type Action Example Description
Convergent Push towards each other Appalachian Mountain Ridge, The Alps, The Himalayas There are two actions here, either one plate can be submerged under another, or the two can push up against each other.
Divergent Pull away from each other Mid-Atlantic Ridge As the plates pull apart, lava from the mantle rises to the ocean floor and solidifies, creating new land in the process.
Transform Slide past each other California coast line The plates grind past each other, sometimes slipping suddenly causing an earthquake.

Part Two: Severity of Earthquakes

  • The severity of an earthquake is determined by both its magnitude and intensity.
  • An earthquake’s magnitude is measured by the Richter scale.
    • Give examples of what a 4 or a 5 on the Richter scale is.
    • This scale is based on the amount of energy released by the earthquake.
    • Discuss how the Richter scale is based on powers of ten. An earthquake that measures a 5 on the Richter scale is ten times more powerful that one that measures a 4.
  • There are many things that are also measured in base 10. For instance:
    • pH– Used to measure the acidity of a solution
      • A solution measuring a 2 on the pH scale has 10 times more hydrogen than one measuring a 3.
    • Decibels (dB)– Used to measure the loudness of sound
      • Though it is based on a base 10 system, a sound is at 50 decibels does not sound like half of a sound that is 100 decibels.
    • Introduce two earthquakes:
      • October 15, 2006 in Hawaii, 6.7 on the Richter scale
      • February 4, 1998 in Afghanistan, 6.1 on the Richter scale
    • Though they are close in magnitude, the damage is very different.
      • Hawaii
        • death toll: 0 people
        • injuries: some minor injuries
        • 1,173 buildings damaged
        • 4 inch tsunami
        • percentage of people who lost power: 95%
      • Afghanistan
        • death toll: 2,323 people
        • injuries: 818
        • homes damaged: 8,049
        • livestock killed: 6,725
    • So how do we measure the intensity of an earthquake that will differentiate the damage done between two earthquakes of relatively the same magnitude? Introduce the modified Mercalli scale.
      • I-XII on the Mercalli scale
      • based on the amount of damage observed after the earthquake
Table 2
Richter Mercalli Description Number each year
1 & 2 I Usually not felt by humans, though animals can get uneasy, detected by instruments. 900,000
II Felt by some people, though few, especially if on upper floors. Hanging objects can sway back and forth. 30,000
3 III Felt indoors, though some may think it’s a passing vehicle. Parked cars may rock. 30,000
3 IV Windows, doors, and shelves are disturbed. Felt indoors. 30,000
4 V Felt by most everyone. Furniture moves. Cracked walls. Trees and poles may shake. Pictures fall off walls. Some people awake to it. 30,000
5 VI Felt by everyone. Some furniture falls over. Some damage. Difficult to stand. Windows may crack. Some plaster falls. Chimneys may be damaged slightly. 30,000
5 VII Poorly constructed buildings are severely damaged. Some walls may fall. Some people fall over. Damage to well constructed buildings as well, though moderate at most. 500
6 VIII Moderate to major damage. Walls and chimneys collapse. Heavy furniture falls over. 100
7 IX Many people panic. All buildings suffer major damage, some collapse. Dams crack. Landslides. Ground noticeably cracked. Pipes break. Buildings shift off foundations. 20
7 X Major damage. Landslides. Railroad lines are bent. Roads crack. Structures destroyed. 20
8 XI Total damage. Bridges destroyed. Wide cracks in the ground. Ground surface waves seen. Buried pipes break. One every 5-10 years
8 XII All manmade structures are destroyed. Ground surface waves seen. Objects thrown into the air. One every 5-10 years

Compiled from the following sources:

PART THREE: Location of the earthquakes

The third part that determines how much destruction of an earthquake is where it occurs. Ask students to speculate which would be worse, an earthquake of magnitude 7 in the middle of the desert, or an earthquake of magnitude 4 in the middle of a major metropolis.

One thing scientists do is determine where the center of the earthquake is (known as the epicenter). This is done by manner or triangulation, or in other words, if you know how far from 3 different locations the epicenter is, you can find the earthquake. Use the accompanying worksheet titled Find that Earthquake! This activity can also be done on Geometer’s Sketchpad.

Triangulation to find the location of something is used not only in seismology, but also in tracking where a cell phone is when being used off of three reception towers, and when using a GPS system in a car. In the final case the location of the vehicle is determined from at least three satellites in the sky.

Sustaining, Concluding, or Extending Activities (optional)

Concluding:

  • Have students predict the destruction of their own town if an earthquake of Richter magnitude 3 were to occur?
  • What about if it was of Mercalli scale IV?

Extending:

  • Using cell tower maps and road maps, have students delve into the idea of triangulation, and what this means geometrically.
  • Using rolls of accounting tape, have students measure powers of ten starting with a 1 millimeter and moving upwards (1 centimeter, 10 centimeters…).

Evaluation and Assessment

Students will be assessed by use of observation of individual and group work during the worksheets and class discussion of the different earthquakes and the damage they caused.

E-Resources, Print Materials, and Hands-on Activities

Growth Worksheet

Find that Earthquake! Worksheet

Information on Modified Mercalli and Richter Scales:

Information on Hawaii and Afghanistan earthquakes: