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7.2 Earthquake Measurement

Learn about major and minor earthquakes, their impact on areas, and the differences in seismic waves. Explore the instruments used to measure earthquakes, such as seismometers and seismographs. Discover how scientists determine the location, magnitude, and intensity of earthquakes. Gain insights into liquefaction and factors affecting earthquake intensity.

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7.2 Earthquake Measurement

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  1. 7.2 Earthquake Measurement

  2. How do major and minor earthquakes affect an area? What causes this difference?

  3. Instruments to record seismic waves • Seismometers • Seismograph

  4. A seismograph detects and records EQs. A seismogram is the EQ record.

  5. Seismology ..\..\..\Desktop\Power point clips\Seismograph.mov ..\..\..\Desktop\Power point clips\Seismograph-Real.mov

  6. Determining Location • Epicenter – point on Earth’s surface directly above an earthquake’s starting point • Focus – the point inside Earth where an earthquake actually begins.

  7. Triangulation • Lag time • time between the arrival of the P waves and the S waves • Tells scientists how far the waves traveled. • Triangulation (point at which all circles intersect in the epicenter) • Epicenter can then be located by drawing circles around at least three seismometer stations

  8. Magnitude • Measure of an earthquake’s strength • The Richter Scale–describe magnitude ranging from 0 to 9 • The Moment Magnitude Scale – • a more accurate measure of the strength of an earthquake • Represents the size of the area of the fault that moves

  9. What is magnitude? Magnitude is the measure of an earthquake’s strength.

  10. Intensity • How the earthquake is felt by people • The Modified Mercalli Scale – describe an earthquake’s intensity ranging from I to XII.

  11. Intensity ..\..\..\Desktop\Power point clips\sf1906-EQintensity.mov

  12. What is intensity? The effects of an earthquake and the way the earthquake is felt by people are called an earthquake’s intensity.

  13. Earthquakes ..\..\video clips\7.2 Earthquake Measurements\Seismology_and_the_Science_of_Earthquakes__Waves__Magnitude__and_the_Richter_Scale.asf

  14. Liquefaction • Process in which loose soil or sediment and surrounding water lose contact with one another. • Intensify ground shaking • Cause the ground to settle

  15. What four factors affect intensity? Four factors that affect the intensity of an earthquake are earthquake magnitude, distance from the epicenter, local geology, and building construction.

  16. Liquefaction Niigata, Japan 1964 Source: National Geophysical Data Center http://abclocal.go.com/kgo/video?id=8060169&syndicate=syndicate&section=

  17. Review Questions • Briefly explain the steps for locating an earthquake’s epicenter. • The time P and S waves take to reach seismometer stations after an earthquake can be used to determine the distance from that station to the epicenter. A circle with a radius equal to that distance is drawn around each of three stations. The point at which these circles intersect is the earthquake’s epicenter.

  18. Compare magnitude and intensity. • Magnitude is the measure of the strength of an earthquake, whereas intensity is a measure of the effects of an earthquake and how the earthquake is felt by people.

  19. 3. Why might an earthquake have more than one intensity value? Explain your answer. An earthquake may have more than one intensity value because the effects of an earthquake may differ with distance from the epicenter, types of building construction, and with the rock type that seismic waves pass through.

  20. Review 7.2 • Earthquake • Seismograph • Focus • Epicenter • Magnitude • Intensity • Richter scale • Modified Mercalli scale • Triangulation • Liquefaction

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