Activity 6: Seismology

SHAKING AND QUAKING, MONITORING EARTHQUAKES

Summary:

Geologists monitor earthquakes to better understand how the crust is affected by movements and to determine how plates are moving. The following activity explains this study, seismology, and how to monitor crustal movement by having students create their own seismograph.

Instructional Method: Activity

Goal: Explain how scientists monitor earthquakes.

Objectives: Students will be able to:

• Make their own seismograph.
• List at least three things about earthquakes.
• Give the name of the instrument used to monitor earthquakes.

Time:

Activity time: 30 minutes
Discussion:15 minutes

Materials Needed:

• a stand or table
• string
• marker or pencil paper

Vocabulary:

earthquake
epicenter
hypocenter
Richter scale
seismic wave
seismograph

Background:

Seismic waves are energy waves produced when friction along a fault causes vibrations in the crust. As energy waves pass through the crust they can be monitored by sensitive devices called seismographs. When evaluating collected data, various scales are used to describe the magnitude of fault movement, inferred from the intensity of the waves.

The magnitude of seismic waves are evaluated according to a Richter scale. This scale is a mathematical computation of the size of the earthquake. Seismographs record zigzag traces showing ground movement beneath the instrument. Sensitive seismographs, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world.

Monitoring earthquakes, all over the world, allows scientists to determine where the earthquake originated. In addition to recording ground motion, seismographs also record the date and time the seismograph felt the waves. Using multiple recordings, scientists are able to calculate where the earthquake originated. The origin of an earthquake is called its hypocenter. This is the point beneath Earth's surface where fault rupture (movement) occurred. The point on the surface that is directly above the hypocenter is called the epicenter.

The following information gives an idea of the characteristics and occurrences of various magnitudes of earthquakes around the world. In the side column there are links that help in further studies of earthquakes.

• Earthquakes with magnitude of about 2.0 or less are usually called micro-earthquakes; they are not commonly felt by people and are generally recorded only on local seismographs.
• Events with magnitudes of about 4.5 or greater - there are several thousand such shocks annually - are strong enough to be recorded by sensitive seismographs all over the world.
• Great earthquakes, such as the 1964 Good Friday Earthquake in Alaska, have magnitudes of 8.0 or higher. (The Good Friday earthquake is the largest earthquake to occur in the United States in recorded history. It measured 9.2 on the Richter scale!) On the average, one earthquake of such size occurs somewhere in the world each year.

The following activity explains how to create your own seismograph. It my not record small earthquakes but can be used to show how it is done in reality. To learn more about seismic waves look at "Surfing Rock Waves".

Instructional Procedures:

1. Make a stand from which to hang a marker by a string.
2. Place a piece of paper below the stand so the tip of the marker is touching the paper.
3. Put your new "seismograph" on a table. Then hit the side of the table with a hammer. It would be a good idea to place a piece of wood between the table and the hammer when you hit it.
4. Notice the different drawings that result from hitting the table. Can you see the push-pull waves? Can you see the side to side waves? Does this work? How can you tell the difference between the waves?

Discussion:

How do geologists know earthquakes are happening even if they can not feel them? Why is it important to monitor earthquakes? Can anyone predict earthquakes? Have you ever felt an earthquake? Did you know how far away it was? How did geologists determine its location, epicenter and hypocenter?

Included National Parks and other sites:

Aniakchak National Monument and Preserve
Bryce Canyon National Park
Denali National Park
Glacier National Park
Great Basin National Park
Hawai`i Volcanoes National Park
North Cascades National Park
Point Reyes National Seashore
USGS Earthquakes Hazard Program
USGS Earthquakes for Kids

Photos:

Normal fault near Bryce Canyon
San Andreas Fault
Seismograph
Thrust Fault

Utah Science Core:

5th Grade Standard 2 Objective 1,2,3

 

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