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EXTREME
NATURAL
EVENTS
1 Earthquakes - Processes
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EARTHQUAKES
WHAT WILL WE BE
LEARNING?
Natural Processes the produce ENE’s
How natural and cultural characteristics/features of an
environment make them vulnerable to the ENE’s
The effects of the ENE on the natural & cultural environment
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The impacts of ENE’s on different groups of people and how they
respond
Earthquakes Geographical Terms
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Tsunami Wave
Noisy
Rumbling
Epicentre
Fault
Focus
Friction
Hazard
Lateral
Magnitude
Seismic
Stress
Subterranean
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Convulsing
Cracking
Crunching
Devastating
Vibrating
Trembling
Fracturing
Frightening
Gaping
Grinding
Mercalli Scale
Richter Scale
Shaking
Shattering
NATURAL PROCESSES
THAT PRODUCE ENE’S
Large earthquakes are usually connected with plate boundaries.
Seismometers record earth movements.
An earthquake is a sudden shockwave caused by rocks being
under stress from movements of plates at plate boundaries.
Eventually the stress in the rock builds up enough to deform and
reach breaking point.
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At that point, the stored up energy is released in the form of a
shockwave.
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EARTHQUAKES &
FAULTS
A fault line is a fracture along which
the crust has moved
Stresses in the crust along NZ’s plate
boundary have broken it into separate
fragments or blocks that move relative
to each other along fault lines.
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Plate tectonics was developed in the
mid 1960’s as a theory to explain
processes and events such as quakes
and vulcanism.
SEISMIC WAVES
Seismic waves are generated when the two sides of the fault
rapidly slip past each other. For most earthquakes, the faults
do not break the surface, so the faults can only be “seen”
through analysing the seismic waves.
Faults can be anywhere from metres to a thousand
kilometres long.
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Link: Different types of faults
WHERE EARTHQUAKES
HAPPEN
Most earthquakes occur along the edge of the oceanic and
continental plates. All but the very deepest earthquakes (deeper
than 600km) occur on faults.
The plates under the oceans are called oceanic plates and the
rest are called continental plates.
The plates are moved around by the motion of a deeper part of
the earth (the mantle) that lies underneath the crust.
These plates are always bumping into each other, pulling away
from each other, or past each other.
Plates usually move at about the same speed that your
fingernails grow.
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Earthquakes usually occur where two plates are running into
each other or sliding past each other.
WHERE EARTHQUAKES
HAPPEN
Earthquakes can also occur far from the edges of plates
along faults.
Faults are cracks in the earth where sections of a plate (or
two plates) are moving in different directions.
Faults are caused by all that bumping and sliding the plates
do.
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They are more common near the edges of the plates.
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FLYOVER OF THE
GREENDALE FAULT
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MAJOR
FAULTS IN NZ
There are major fault lines
running the length of New
Zealand
The Alpine fault carries most
of the total plate boundary
strain
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It is a very distinct feature
along most of its length
because o f the Southern
Alps that have been uplifted
along the eastern side
making it clearly visible from
space.
HIKURANGI TRENCH
This is a broad, deep-sea trough (or subduction zone) that
lies less than 100km off the east coast of the North Island
and runs south to the waters off Kaikoura
It marks the boundary between two crustal plates and the
margin where the Pacific Plate (to the east) is being dragged
underneath the Australian Plate.
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Large tsunamis, such as the 2004 Indian Ocean tsunami, are
most frequently caused by earthquakes on plate boundaries
where subduction takes place.
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HIKURANGI TRENCH
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WHERE TWO TECTONIC
PLATES COLLIDE
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CHRISTCHURCH
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HOW DO YOU
MEASURE IT?
Question - How are earthquakes measured?
The Richter Scale
•  On this scale, the magnitude of an earthquake is expressed in whole
numbers and decimal fractions. It is not used to express damage.
The modified Mercalli Scale
This is the intensity value assigned to a specific site after an
earthquake and has a more meaningful measure of severity to a non
scientist than the magnitude because intensity refers to the effects
actually experienced.
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• 
MEASURING
EARTHQUAKES
Earthquakes were traditionally measured on the Richter
scale.
Now they are measured using the Moment Magnitude Scale
(Magnitude scale)
•  This measures the size of the seismic waves during an
earthquake.
The amount of damage caused by an earthquake is measured
by the Mercalli Scale.
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•  This is a measure of intensity
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Using the guide on the next page, illustrate the impacts of an
earthquake at each magnitude on the Richter Scale.
SEISMIC WAVES
Earthquakes produces shock waves that
cause damage.
There are two types of seismic waves
* P-waves (longitudinal/faster/travel
through solids and liquids) – like sound
waves
* S-waves (transverse/slower/travels
through solids only)
– like light waves
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Seismometers can detect these waves and
provide evidence of the Earth’s surface
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BODY WAVES
These waves travel through the Earth
P-waves are the fastest type of seismic wave.
As P-waves travel, the surrounding rock is repeatedly
compressed and then stretched.
S-waves arrive after P-waves because they travel more
slowly.
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The rock is shifted up and down or side to side as the wave
travels through it.
SURFACE WAVES
These travel over the Earth’s surface
Rayleigh waves (also called ground roll) travel like ocean
waves over the surface of the earth moving the ground
surface up and down.
They cause most of the shaking at the ground surface during
an earthquake.
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Love waves are fast and move the ground from side to side.
MAPPING THE DEADLIEST
EARTHQUAKES
You will be given a table of earthquakes and a world
map
Use the map to present the information in the table.
Your final map should:
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•  Be easy to understand. This includes usin g
coloured pencils, rulers, horizontal labels etc
•  Contain all the relevant information in the table
•  Follow mapping convensions
•  Title, key, orientation, scale
Once complete, answer the questions on the separate
handout