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# Earthquakes and volcanoes

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## Abby Harris

on 28 April 2010

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#### Transcript of Earthquakes and volcanoes

Everything you've ever wanted to know about EARTHQUAKES
Given what we have been talking about the past few days- where do you think volcanoes and earthquakes are most likely to happen?
What causes earthquakes?
When plates move, their edges get stressed out.
If the plates cannot move where they want, energy from stress on the rocks will build up.
The stress will becomes so great that the rock will snap!
Seismic Waves
the movement that causes the shaking we feel
Focus!
Epicenter
The exact point INSIDE the earth where the earthquake starts.
The point directly above the focus on the earth's surface, damage is greatest here, but can happen anywhere within a few km from the epicenter
Waves move in all directions from the focus
SHOCK WAVES!
Primary "P" waves
Secondary "S" Waves
Longitudinal waves
Moves fastest
Moves by compressing and stretching rock
Transverse waves
Moves slower
Moves in waves like a rope shaken up and down
Both move in all directions from the focus
Surface Waves
Moves only on the surface
Caused by the movement of Earth as a whole- bends shakes and rolls
Most destructive!
Seismographs measure P and S waves
Based on the P and S waves, scientists can calculate the epicenter of the earthquake
The Richter scale measures the energy released by a quake
The amount of damage caused depends on the distance between populated areas and the epicenter, depth of the focus, and type of soil
So does the energy matter that much in some areas?
How do you think scientists predict earthquakes, is it easy?
Following P and S waves through the earth can give us an idea of the earth's composition
Full transcript