Transcript Earth Science Review - Cashmere

The earth and how it moves
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This is a theory that the earth’s crust is made
up of several “plates” that move past one
another.
It has been suggested that at some point all
of these plates were all together in one
massive continent called Pangea
200 Million Years
Ago
135 Million Years
Ago
65 Million Years Ago
Present Day
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There are different types of boundaries that
occur between plates
Destructive boundaries:
Subduction zones where ocean
crust is pushed bellow
continental crust and melts
Constructive boundaries:
Mid Ocean Ridges were
ocean crust is made
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Movements in the earth’s crust that can cause
huge amounts of damage
But some may ask – Can they be prevented?
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Earthquakes are measured on two different
scales.
The Mercalli Scale – Measures the damage
done at a particular location.
The Richter Scale – Measures the magnitude
of the earthquake (how much energy is
released) on a scale of 1 to 10.
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A seismograph is an instrument which
measures the movements of the ground.
It shows this movement on a continuous zigzag line.
A seismograph will show 3 periods of
shaking. One for the arrival of each type of
wave.
September 1985
Mexico City
8.1
Killed 7000
1964
Alaska
9.2
Killed 131
October 1989
San Fransisco
7.1
Killed 62
January 1995
Japan
7.2
Killed 6400
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3 different waves move through rock like
ripples in a pond.
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P-Waves or primary waves are the first waves
to hit as they move the fastest (8km/s). They
squeeze and stretch the rock.
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The next waves to hit are the secondary
waves (S-Waves). These waves move at
5km/s and make the ground shake up and
down as well as from side to side.
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Traveling at 4km/s are the last waves to hit,
the L-Waves. These waves do the most
damage as they travel near the surface of the
crust.
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All three together.
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Do you think they can be prevented?