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Earthquake Waves Chapter 6-2

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Focus and epicenter Actual location of fault Up to 700 km below surface

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Focus and epicenter Surface location directly above the focus Actual location of fault Up to 700 km below surface

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P-waves Primary waves -Compression waves -Travel in a horizontal direction -First to arrive at a distant location

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S-waves Secondary waves - vibrate at right angles to p-wave - particles move back and forth but wave moves forward - second to arrive at distant location

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Surface Waves Surface waves - travel parallel to Earth’s surface - have greatest height - move like an ocean wave - last to arrive at distant location - are responsible for damage

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Locating Epicenter Time lag between P-wave and S-wave indicate how far the earthquake is from a seismograph station. Lag Time

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Locating Epicenter The lag time tells us how far we are from an earthquake but not from which direction Epicenter can be any where on radius of the circle

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Locating Epicenter At least ____ seismograph stations are needed to pinpoint the epicenter of an earthquake Infinite number of possible epicenters

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Locating Epicenter At least ____ seismograph stations are needed to pinpoint the epicenter of an earthquake Possible epicenter Possible epicenter Two seismograph stations narrow possible epicenters down to two

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Locating Epicenter At least three seismograph stations are needed to pinpoint the epicenter of an earthquake Three epicenters narrows possible locations down to one epicenter

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DEMO

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Measuring Earthquakes Mercalli Scale - rates earthquake according to level of damage at a given location - 12 steps to scale - same earthquake can have different rating at different locations

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Measuring Earthquakes Richter Scale - rates earthquake’s magnitude based on size of seismic waves - works well with small, nearby quakes - waves are measured by a seismograph

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Measuring Earthquakes Moment Magnitude Scale - estimates the total energy released by an earthquake - can rate all earthquakes - scientists look at type and strength of waves, amount of movement, and strength of rocks that broke

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