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EARTHQUAKES
Science Unit
(Planet Earth & Beyond)
Term 1 2011
LEARNING INTENTIONS
1. To identify features of
the earth’s structure.
LEARNING INTENTIONS
2. To understand how
natural forces cause
earthquakes.
LEARNING INTENTIONS
3. To explore the impact
of earthquakes in NZ.
LEARNING INTENTIONS
4. To learn what to do
before, during and after
an earthquake has
struck.
THE EARTH’S STRUCTURE
WHY DO EARTHQUAKES HAPPEN?
Plate Tectonics
New Zealand is right on the edges of two tectonic
plates – the Australian and Pacific – and we get
plenty of the action that goes with it!
TECTONIC PLATES
Tectonic plates cause :
earthquakes,
volcanoes,
geothermal activity,
tsunamis and landslides.
Transform boundaries – The plates move past each other,
but because of friction, they cannot just glide past each
other so build up stress, which is released as an
earthquake.
Divergent boundaries – The plates slide apart from each
other and the space that this creates is filled with new
crust from the magma formed below in the
asthenosphere.
Convergent boundaries – The plates slide towards each
other and moves underneath the other. This is a
subduction zone, making deep marine trenches and
volcanoes, some of the most explosive on earth.
At a subduction zone, two tectonic plates try to
pass each other. Along faults, rocks grind past each
other.
Instead of sliding, some rocks lock together – but
they are still being pushed, so they bend and
stresses build up.
Eventually, the pressure becomes too much, and
the two sides of a fault jerk past each other. This
releases stored energy as shock waves (called
seismic waves) that travel out from the centre
through the surrounding rock, sometimes to the
other side of the world.
WHY DO EARTHQUAKES HAPPEN?
THE MAGNITUDE
SCALE
Scientists use seismographs to measure
when the seismic waves reach three
different points, and they can work out
where the focus and epicenter are. They
also use the waves to work out the
magnitude of the earthquake, normally
measured on the Richter scale.
GeoNet
SEISMOMETER
NETWORK
This map shows the
distribution of the main
seismometers used to detect
earthquakes around New
Zealand. During periods of
seismic activity, temporary
stations are also set up to
gather more information.
EARTHQUAKES IN NEW ZEALAND
About 14,000 earthquakes
are recorded in and around
New Zealand every year.
Fortunately, most of them
are too small for us to feel at
the surface. However, many
of us have felt the shake of
an earthquake, and there are
some big ones that have
become part of New Zealand
history.
EARTHQUAKES IN NEW ZEALAND
Just offshore from the
North Island, the Pacific
Plate begins to descend
beneath the continental
crust on the Australian
Plate. The descending
plate presses against the
overlying continental
plate, causing the
overlying plate to fracture
and producing shallow
earthquakes. Deep
earthquakes occur in the
oceanic crust that is being
bent downward into the
subsurface.
CHRISTCHURCH 2010
The Christchurch
earthquake was a
7.1 magnitude
earthquake which
struck at 4:35 am on
4 September 2010.
The quake caused
widespread damage
and several power
outages in New
Zealand's second
largest city.
Two residents were seriously injured, one
by a collapsing chimney and a second by
flying glass. One person died of a heart
attack suffered during the quake.
The earthquake's epicentre was
40 kilometres (25 mi) west of
Christchurch, near the town of
Darfield. The hypocentre was at
a shallow depth of 10 km. A
foreshock of roughly magnitude
5.8 hit five seconds before the
main quake. The initial quake
lasted about 40 seconds, and
was felt widely across the South
Island, and in the North Island as
far north as New Plymouth.
About 100 faults
and fault
segments have
been recognised
around the
region, some as
close as 20 km
to central
Christchurch.
Aftershocks
THE COST
Earthquake Commission
(EQC), private insurance
and individual costs may
reach as high as
$4 billion
dollars !!!!!!
How do we prepare for an
earthquake?
Develop a Household Emergency Plan.
Assemble and maintain your emergency survival items
for your home as well as a portable getaway kit.
Practice Drop, Cover and Hold.
How do we prepare for an
earthquake?
Identify safe places within your home, school or workplace.
1) Somewhere close to you, no
more than a few steps or less than
three metres away, to avoid injury
from flying debris.
2) Under a strong table.
3) Next to an interior wall, away
from windows that can shatter and
cause injury and tall furniture that
can fall on you.
What do we do during an
earthquake?
•If you are inside a building, move no more than a
few steps, drop, cover and hold. Stay indoors till
the shaking stops and you are sure it is safe to exit.
In most buildings in New Zealand you are safer if
you stay where you are until the shaking stops.
•If you are outside, move no more than a few
steps away from buildings, trees, streetlights and
power lines, then drop, cover and hold.
•If you are at the beach or near the coast, drop,
cover and hold then move to higher ground
immediately in case a tsunami follows the quake.