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**Measuring Earthquakes**

How are earthquakes measured?

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**Seismology The study of earthquake waves is called Seismology**

Earthquake waves can be detected at great distances by Seismometers A seismometer’s record is known as a seismogram

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Time-Travel Curves Years of data collection has led to time-travel curves The curves tell the time an S- and P-wave takes to reach a certain distance P-waves arrive first The difference between waves on a seismogram determines the distance from the epicenter

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Time-Travel Curves

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Locating Earthquakes Epicenters are located by the separation between S- and P- waves on a seismogram Cannot use one location to map epicenter Need to use three or more seismic stations Time can be measured in same way

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Earthquake Intensity The amount of energy released during an earthquake is known as its magnitude Three scales measuring intensity Richter Scale Moment Magnitude Scale Modified Mercalli Scale

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Richter Scale The Richter Scale is based on the largest waves generated by the quake Each number on the scale is an increase of 10 Ex: 8 is 10x larger than 7, 100x larger than 6

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**Moment Magnitude Scale**

The Moment Magnitude Scale includes: Size of fault rupture Amount of movement along fault Rocks’ stiffness Uses more data than Richter Scale – More accurate

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**Modified Mercalli Scale**

The Modified Mercalli Scale assesses damage from a quake

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**Factors affecting Magnitude**

Distance from epicenter Depth of focus

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**Where do Earthquakes Occur?**

Earthquakes are not randomly distributed Almost 80% of Earthquakes occur along the Circum-Pacific Belt

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