1. Earthquake Measurement
7.2
Earthquake Measurement

2. How do major and minor earthquakes affect an area
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
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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. Magnitude is the measure of an earthquake’s strength.
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.

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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. Earthquake s
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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. Source: National Geophysical Data Center
Liquefaction
Niigata, Japan 1964
Source: National Geophysical Data Center

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
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