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1.16 Science Event:
Earthquakes in Christchurch
Achievement Standard
Achievement Standard Science 90955: Investigate an astronomical or Earth
science event
Resource reference: Science 1.16B v2
Resource title: Earthquakes in Christchurch
Achievement with
Merit
Investigate an
Investigate, in-depth,
astronomical or
an astronomical or
Earth science event. Earth science event.
Achievement
Credits: 4
Achievement with
Excellence
Investigate,
comprehensively, an
astronomical or Earth
science event.
Focus Questions

What internal processes (plate tectonics) were involved in causing the Christchurch earthquakes?

Why do so many earthquakes occur in New Zealand compared to other countries?

What is a fault and which one/s were involved in the Christchurch Earthquakes?

Why was the February 22nd earthquake considered an aftershock from the September 4th
earthquake?

Why was the magnitude 6.3 earthquake in February able to cause so much more destruction
around Christchurch than the magnitude 7.1 quake in September 2010?

What are seismic waves and how do they cause the ground to shake so strongly?

How is shaking recorded?

Why did people hear a loud rumble before the shaking began?

What is liquefaction and what causes it?

Why did liquefaction cause so such damage in some areas?

Why were some buildings more likely to be damaged during the Christchurch Earthquakes?

Why didn’t a tsunami occur?

Which departments/groups/organisations are responsible for earthquake research in New
Zealand?
What does the Earths interior look like?
The thin layer of solid rock which covers the Earth is called the crust.
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What does the Earths interior look like?
The crust is made up of
the thick continental
crust that forms the land
and the much thinner
oceanic crust that makes
up ocean floors.
What does the Earths interior look like?
Under this is the
mantle.
The middle of this is
molten - so the
upper mantle and
crust float on this.
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What does the Earths interior look like?
The inner layer is the
core, which is a solid
core surrounded by
molten rock.
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How do we know what the Earths interior look like?
When earthquakes occur
they send waves through
the earth. Different types of
material with different
temperatures will cause the
waves to bend in different
ways.
Seismologists (earthquake
scientists) record where in
the world the waves come
out and use that information
to work out the size of
layers, what the
temperature of them is and
what they are made out of.
Plate Tectonics
The earth’s crust is
divided into
different sized
pieces called plates.
They fit together to
cover the earth.
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Plate Tectonics
 The plates float on hot, semi molten
magma
 Deep in earths core nuclear
reactions release huge amounts of
heat energy. This heat is the main
source of energy for moving the
gigantic plates
 This heat causes the magma in the
lower mantle rock to expand and
become less dense.
 This magma rises in convection
currents
 When the magma currents get near
the crust they are pushed sideways
and travel in different directions
 These immensely powerful currents
slowly float the huge tectonic plates
across the planets surface
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Plate Tectonics
The Lithosphere, the crust and top
part of the mantle, is divided into
large areas called plates, which
are constantly moving
The plates move slowly over the
asthenosphere, which is the
molten layer in the mantle, about
3cm a year.
They can move towards each other,
apart from each other or shift
sideways
Because all plates fit together,
movement of one plate effects
all plates around it
The study of plate movement is
called plate tectonics
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Evidence for Plate Tectonics
 Evidence supports the conclusion
that 200 million years ago, at the
start of the Mesozoic era, all the
continents were attached to one
another in a single land mass, which
has been named Pangaea.
 During the Triassic, Pangaea began
to break up, first into two major land
masses:
 Laurasia in the Northern Hemisphere
and
 Gondwana in the Southern
Hemisphere.
 The present continents separated at
intervals throughout the remainder
of the Mesozoic and through the
Cenozoic, eventually reaching the
positions they have today.
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Evidence for Plate Tectonics
Shape of the Continents – close fit of continents
 The east coast of South America and the west coast of Africa match
especially at the boundaries of the continental slopes rather than the
shorelines.
Geology – similar rock patterns
 In both mineral content and age, the rocks on the coast of Brazil match
precisely those found on the west coast of Africa.
 The low mountain ranges and rock types in North America match parts
of Great Britain, France, and Scandinavia.
Fossils – patterns in distribution
 The same fossil reptiles found in South Africa are also found in Brazil and
Argentina.
Evidence for Plate Tectonics
The continents
have gradually
moved from one
large land mass
into the
continents we
know today. This
movement has
been slow but the
time scale is
large. The
continents are
still moving
today.
Plate Tectonics
Plate Movement
When plates move the continents sitting on
top of them move as well.
Plates can either;
 Move away from each other – divergent
boundary
 Move towards each other – convergent
boundary
 Move sideward pass each other –
transverse boundary
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Divergent Boundary
A divergent boundary is where
the tectonic plates are
separating.
New crust is made from cooling
magma oozing up between
the plates
Some spreading boundaries are
places where the crust is
sinking downward as it is
stretched thin
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Convergent Boundary
A Convergent
Boundary is the
opposite of a
divergent
boundary.
Typically you will
see a converging
boundary on a
tectonic plate
that is on the
opposite side of
a divergent
boundary
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Convergent Boundary
Sometimes you'll see volcanic activity at converging boundaries where
plates are crashing into each other.
When one plate (usually the lighter continental crust) rides up over the
top of the other it's called a Subduction zone
one plate margin slides under the other and melts into magma as it moves
downwards
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Convergent Boundary
As a plate moves in one
direction it collides with
the adjacent plate on its
"front" end, while the
trailing end of the plate is
being pulled and
stretched (spreading)
from the plate on the
other end.
The colliding plates can
cause a pushing up of land
and the forming of a
mountain range along the
edge of a plate.
Transform fault Boundary
Transform fault
boundaries are places
where the two plates
are just sliding past
each other. Of major
importance are the
earthquakes that are
triggered along fault
boundaries.
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Transform fault Boundary
Fault seen through plantation
Aerial view of the San Andreas
fault slicing through the Carrizo
Plain in the Temblor Range
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Plate Boundary Summary
Plate Boundary Summary
Divergent Boundary
Convergent Boundary
Transform plate Boundary
What causes earthquakes
Earthquakes occur
when two tectonic
plates move suddenly
against each other. The
rocks usually break
underground at the
hypocentre and the
earth shakes. Waves
spread from the
epicentre, and the
point on the surface
above the hypocentre.
If a quake occurs under
the sea it can cause a
tsunami.
In a strike-slip fault, the blocks of rock
move in opposite horizontal
directions. These faults form when
crust pieces slide along each other at
a transform plate boundary.
What causes earthquakes
As plates move the strain causes brittle rock to crack
These cracks, called faults, are often weak zones where more movement
or cracking may occur
Constant movement of plates causes pressure to build up at faults, and at
the boundaries of the plates
If there is a sudden slippage of rock, this pressure is released quickly and
an earthquake occurs
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The Alpine fault
The Alpine Fault, is about 600km
through the middle of the South
Island. It’s the boundary of the
Pacific and Australian Plates.
Horizontal movement of the
Alpine Fault is about 30m per
1000 years, very fast by global
standards.
A new fault line was discovered
when the February 22
Earthquake occurred in
Christchurch. This was an
extension off the Alpine fault and
was in the form of a strike slip
fault
Earthquake waves
Earthquake waves
There are 3 main types of seismic waves are generated when faulting triggers an
earthquake. All the seismic waves are generated at the same time, but travel at different
speeds and in different ways. Body waves penetrate the earth and travel through it, while
surface waves travel along the surface of the ground.
Primary and secondary waves are body waves. Primary waves (P-waves) travel the fastest
and can move through solids and liquids. The P-wave energy causes the ground to move in
a compressional motion in the same direction that the wave is traveling. Secondary waves
(S-waves) are slower and travel only through solids. The S-wave energy causes the ground
to move in a shearing motion perpendicular to the direction of wave movement.
Surface waves can cause rolling motion
or sideways movement. These waves
results in ground heave and swaying
buildings. Surface waves cause the
most devastating damage to buildings,
bridges, and highways.
Liquefaction
Why Does NZ have so many earthquakes?
New Zealand is on
the top of two plates
moving with
transverse motion.