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What are earthquakes?
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Words to know Earthquake – Focus – Epicenter – Seismic Wave –
a vibration of the earth (affects large area) the point where the earthquake starts the point on the earth’s surface directly above the focus energy sent out from an earthquake
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Facts Most earthquakes occur along faults (where two plates touch) when potential energy is changed to kinetic energy. There are more than 3,000,000 earthquakes every year. = 8,000 a day = 1 every 11 seconds (According to the United States Geological Survey) Most of these are NOT felt by humans.
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Earthquakes to know 1906 – San Francisco
~ 60 times more energy than the ’89 quake 1989 – San Francisco (Loma Prieta)
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Notes There are 2 types of Seismic Waves 1.) Body Waves –
Primary Waves (p-waves) Faster Travel through solid and liquid rock Travels as a longitudinal wave Secondary Waves (s-waves) Slower Travel through solid rock (not outer core) Travels as a transverse wave travel through earth’s body (interior)
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Notes 2.) Surface waves – travel through the earth’s surface (crust)
usually responsible for shaking the ground Sideways Wave Shakes the ground from side to side like a snake Up-and-Down Wave Can open and close cracks in the earth travel through the earth’s surface (crust)
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How are earthquakes detected?
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Words to know Seismograph –
Seismogram – a device that is used to measure earthquakes the paper with the zigzag lines (created by a seismograph)
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How are earthquakes measured?
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Notes There are 2 scales used to measure earthquakes:
1.) Richter Scale very accurate because it uses a seismograph to measure the ground motion tells magnitude of earthquake on a scale from 1 – 10 (10 is largest magnitude) 2.) Mercalli Scale inaccurate because scale is based on eye witnessed destruction from earthquake scale in roman numerals from I – XII
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