Ch12 earthquakesandvolcanoessection1
Transcript of Ch12 earthquakesandvolcanoessection1
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The Changing Earth
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Chapter Twelve: Earthquakes
• 12.1 Earthquakes
• 12.2 Volcanoes
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Investigation 12A
• What conditions affect the timing, duration, and intensity of an earthquake?
Earthquakes
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12.1 What is an earthquake like?• The second longest ever
recorded earthquake occurred in 1964 in Alaska and lasted for four minutes.
• During an earthquake, strong shaking makes the ground move up and down and back and forth.
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12.1 What is an earthquake like?• Foreshocks are small
bursts of shaking that may precede a large earthquake.
• Aftershocks are small tremors that follow an earthquake, lasting for hours or even days after the earthquake.
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12.1 What causes earthquake?
• An earthquake is the movement of Earth’s crust resulting from the release of built-up potential energy between two stuck lithospheric plates.
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12.1 What causes earthquakes• The point below the surface where the
rock breaks is called the earthquake focus.
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12.1 What causes earthquakes?• As soon as the rock breaks, there is
movement along the broken surface causing a split in the surface called a fault.
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12.1 What causes earthquakes?• The seismic waves from an earthquake are
usually strongest at the epicenter, the point on the surface right above the focus.
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12.1 Stick-slip motion
• An earthquake is a form of stick-slip motion.
• Stick-slip motion can be compared to a stuck door.
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12.1 Stick-slip motion• Three conditions are needed for stick-slip
motion:1. Two objects that are touching each other
where at least one of the objects can move.2. A force, or forces, that will cause the
movement.3. Friction strong enough to temporarily keep
the movement from starting.
Use the stick-slip door model to identify these conditions.
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12.1 Friction
• Friction is a resistance to slip that occurs when two objects rub against each other.
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12.1 Lithospheric plates have many sections
• A moving line of grocery carts is a better example of a moving lithospheric plate.
• Although a plate may be moving as a single unit, its boundaries act like they were made of many small sections like the line of carts.
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12.1 Lithospheric plates have many sections
• A lithospheric plate may be thousands of km. across.
• It takes a long time for movement on one end of the plate to affect a section further away.
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12.1 When do earthquakes happen?• The release of built-up potential energy causes
earthquakes.• An earthquake is a stress reliever for a lithospheric
plate.• Once a quake occurs, potential energy builds up
again.
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12.1 Seismic waves• Seismic waves are recorded and measured
by an instrument called a seismograph.• Seismic waves inside Earth are called body
waves. • The two main types of body waves are P-
waves and S-waves.
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12.1 Seismic waves• After an earthquake
occurs, the first seismic waves recorded will be P-waves.
• S-waves are recorded next, followed by the surface waves.
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12.1 Seismic waves• In a quarter-mile race,
the track is so short that fast and slow cars are often just fractions of a second apart.
• In a long race, like the Indianapolis 500, the cars might be minutes apart.
• The time difference between slow and fast cars is related to the length of the race track.
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12.1 Seismic waves• Seismic waves radiate from
the focus after the earthquake.
• Three seismic stations can accurately determine the times of body wave arrival.
• The larger the difference in arrival time, the farther the epicenter is from the station.
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12.1 Seismic mystery
• Garrett Euler was puzzled because earthquake-like signals were arriving at all of his 32 seismic stations at the same time.
• Euler was able to show that each burst of seismic signals matched the time each Cameroonian soccer goal occurred!
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12.1 Measuring seismic waves• The Richter scale ranks earthquakes according
to their magnitude of the seismic waves recorded on a seismograph.
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12.1 Measuring earthquake damage
• The Modified Mercalli scale has 12 descriptive categories.
• Each category is a rating of the damage experienced by buildings, the ground, and people.
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12.1 Earthquakes and plate boundaries
• Earthquakes commonly occur at the boundaries of lithospheric plates.
• This is because plate boundaries tend to be zones of seismic activity.
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