1. Section 3: Measuring and Locating Earthquakes
Scientists measure the strength and chart the location of earthquakes using seismic waves. K
What I Know W
What I Want to Find Out L
What I Learned

2. Essential Questions
What are earthquake magnitude and intensity and how are they measured?
Why are data from at least three seismic stations needed to locate an earthquake’s epicenter?
Where are Earth’s seismic belts?
Measuring and Locating Earthquakes
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3. Vocabulary Review New plot Richter scale magnitude amplitude
moment magnitude scale
modified Mercalli scale
Measuring and Locating Earthquakes
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4. Earthquake Magnitude and Intensity
Richter scale
The Richter scale, devised by a geologist named Charles Richter, is a numerical rating system that measures magnitude of an earthquake.
Magnitude is the measure of the energy released during an earthquake.
The numbers in the Richter scale are determined by the height, called the amplitude, of the largest seismic wave.
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Measuring and Locating Earthquakes

5. Earthquake Magnitude and Intensity
Moment magnitude scale
The moment magnitude scale is a rating scale of the energy released by an earthquake, taking into account the size of the fault rupture, the amount of movement along the fault, and the rocks’ stiffness.
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Measuring and Locating Earthquakes

6. Earthquake Magnitude and Intensity
Modified Mercalli scale
The modified Mercalli scale is used to measure earthquake intensity on a scale from I to XII. The higher the number, the greater the damage the earthquake has caused.
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Measuring and Locating Earthquakes

7. Add link to Animation from p. 540 here.
Modified Mercalli scale
Concepts In Motion
FPO
Add link to Animation from p. 540 here.
Measuring and Locating Earthquakes
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8. Earthquake Magnitude and Intensity
Modified Mercalli scale
The intensity of an earthquake depends primarily on the amplitude of the surface waves generated. Maximum intensity values are observed in the region near the epicenter; Mercalli values decrease to I at distances far from the epicenter.
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Measuring and Locating Earthquakes

9. Earthquake Magnitude and Intensity
Depth of focus
Earthquakes are classified as shallow, intermediate, or deep, depending on the location of the focus. Shallow-focus earthquakes are the most damaging.
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Measuring and Locating Earthquakes

10. Locating an Earthquake
The location of an earthquake’s epicenter and the time of the earthquake’s occurrence are usually not known at first. However, the epicenter’s location, as well as the time of occurrence, can be determined using seismograms and travel-time curves.
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Measuring and Locating Earthquakes

11. Locating an Earthquake
Distance to an earthquake
Seismologists determine the distance to an earthquake’s epicenter by measuring the separation on any seismogram and identifying that same separation time on the travel-time graph.
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Measuring and Locating Earthquakes

12. Locating an Earthquake
Distance to an earthquake
To locate the epicenter of an earthquake, scientists identify the seismic stations on a map, and draw a circle with the radius of distance to the epicenter from each station. The point where all the circles intersect is the epicenter.
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Measuring and Locating Earthquakes

13. Locating an Earthquake
Time of an earthquake
Seismologists can use a seismogram to gain information about the exact time that an earthquake occurred at the focus. The time can be determined by using a table similar to a travel-time graph.
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Measuring and Locating Earthquakes

14. Seismic Belts
The majority of the world’s earthquakes occur along narrow seismic belts that separate large regions with little or no seismic activity.
The locations of most earthquakes correspond closely with tectonic plate boundaries.
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Measuring and Locating Earthquakes

15. Review Essential Questions Vocabulary
What are earthquake magnitude and intensity and how are they measured?
Why are data from at least three seismic stations needed to locate an earthquake’s epicenter?
Where are Earth’s seismic belts?
Vocabulary
Richter scale
magnitude
amplitude
moment magnitude scale
modified Mercalli scale
Measuring and Locating Earthquakes
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