Download Y10 Earthquakes - Learning on the Loop

Y10 Earthquakes
Geological processes
Meulaboh – the epicentre
Earthquake video
What is an earthquake?
What happens in an earthquake?
What is the effects of an earthquake on
the community?
What should you do in an earthquake?
What shouldn’t you do?
A rupture along a fault line
Earthquake commission
Fix. Fasten. Forget.
Secure hot water cylinders and header tanks
Check that your house is secured to its foundations
Secure your chimney with galvanised metal bands
Secure tall furniture to the wall studs
Secure wood burners to the floor
Store heavy objects low down
Use non-slip mats under smaller appliances and
objects
Use plastic putty (Blu Tack) to secure ornaments
Push picture and mirror hooks closed
Have flexible gas and plumbing fittings installed.
What to do during an Earthquake
Follow this link for ideas what to do in an
earthquake
FEMA: What to Do During an Earthquake
Te Anau Earthquake video
Click on the links below
Earthquakes - Earthquake damage, Te
Anau - Te Ara Encyclopedia of New
Zealand
Earthquake Definitions
An earthquake is vibrations of the Earth
produced by the rapid release of energy.
Surface rocks of the Earth’s crust are
brittle and can break when put under
pressure.
Deeper rocks bend under pressure as they
are not so brittle.
Focus, epicentre and fault
Focus – the point where the rock breaks in
the Earth’s crust.
Epicentre – The point on the Earth’s crust
directly above the focus.
Fault – break in the rocks of the crust
where the two sides of the break have
moved relative to each other.
Fault, focus and Epicentre
Active faults
Many fault lines cut the
ground’s surface in New
Zealand; each past fault
movement would have
been accompanied by a
large earthquake.
Those that are considered
likely to move again in the
future are called active
faults. They are known to
have ruptured the ground
surface once or more in
the last 120,000 years.
This map effectively
shows the areas where
future earthquakes are
most likely.
Questions
Why do Earthquakes occur in the crust
and not deeper in the mantle?
What is the difference between focus and
epicentre?
Weblink to show NZ earthquakes
Click on the link below.
Earthquakes - New Zealand earthquakes,
1990–94 - Te Ara Encyclopedia of New
Zealand
New Zealand
regions at
greatest risk of
ground shaking
The difference
between each
level is 10%.
What do you
notice about the
distribution of
more severe
earthquakes?
The 1848 Marlborough Earthquake
and 1929 Murchison Earthquake.
Click on the links below
Historic earthquakes - The 1848
Marlborough earthquake - Te Ara
Encyclopedia of New Zealand
Historic earthquakes - The 1929 Arthur’s
Pass and Murchison earthquakes - Te Ara
Encyclopedia of New Zealand
Earthquakes - Seismic Waves
Waves travel outwards from the focus
Three types, in the order they arrive:
1. P Waves (primary) – longitudinal waves
causing compression and extension of
rocks. Moves through solid an liquid.
2. S waves (secondary) – transverse waves
sideways and vertical shaking. Can’t
move through liquids.
3. Surface waves – slow. Travel through
crust like ocean waves. Cause most
damage.
Earthquake wave animation
Earthquakes - Primary and secondary
waves - Te Ara Encyclopedia of New
Zealand#breadcrumbtop
Seismologists
Seismologist are scientists who study
Earthquakes.
Seismographs are instruments which
record seismic waves.
Seismograms are the recordings they
make.
A seismograph
seismograph
A seismogram
Seismologist, ha ha!
Finding an epicentre
Seismologist use the time interval between
the arrival of the P and S waves to
determine their distance from the
epicentre.
When the arrival times of P and S waves
from three seismographs in different
locations are recorded, the epicentre can
be calculated.
Measuring Earthquakes
Measured by Intensity and Magnitude
Intensity – Mercalli scale – based on
people’s experiences and effects on
buildings and the environment.
Magnitude – Richter scale – based on
amount of energy released.
Measurements of ground movements and
seismographs.
Damage from Earthquakes
Depends on size, distance from focus,
type of rock, strength of buildings and
depth.
Richter scale – not linear, each step
releases 30x more energy.
Make your own seismograph
Make an earthquake and bring
in your seismograph and
seismogram
Earth’s Structure
Structure of Earth
Crust - 6km thick under oceans – solid
- up to 70 km thick under
continents. Av: 30-40 km
Mantle- 3 000 km thick – plastic – flows
- upper 100 km – rigid
Outer core – 2,300 km thick – liquid
Inner core – 1,200 km thick - solid
The bits
Continental crust is under the continents,
its light and floats on the mantle. Oldest
rocks.
Oceanic crust is heavier, thinner, less
buoyant, sinks into mantle.
Mantle rock is hot and under pressure so
isn’t actually melted.
Core is mainly iron and nickel.
Circulation of iron produces magnetic field.
Tectonic plates
Tectonic plates in 3D
Convection currents in mantle
Heat from the
core heats the
magma
causing it to
rise towards
the crust in
currents which
push on the
plates, moving
them.
What happens when plates move?
Spreading zones –
plates move apart at
mid-oceanic ridges.
Magma rises to form
new crust in the gaps.
Where does the old oceanic crust
go?
Collision zones – plates collide at
boundaries.
Rocks can fold into mountains like the
Southern Alps.
Earthquakes common
Subduction – a less dense oceanic plates
goes in under a continential coast – east
of the North Island.
Subduction of the pacific plate
under the north island
Mountain building – folding rocks
Movement of tectonic plates
Plate
boundaries
through New
Zealand.
The pacific
plate is
subducting
under the
Australian in
the north and
colliding in
the south.
Valley formed by the
subsidence of a block
of the Earth's crust
between two or more
parallel faults.
Rift valleys are steepsided and form where
the crust is being
pulled apart, as at
mid-ocean ridges, or
in the Great Rift
Valley of East Africa.
Active volcanoes of the Pacific
The Geological History of NZ
Gondwana
NZ was formed off
the coast of the
great southern
supercontinent –
Gondwana.
The oldest rocks in
NZ are about 500
MY old.
150 mya
Rocks formed
from sediments
eroded off
gondwana are
uplifted due to a
subduction zone
forming.
Greywacke forming at the edge of
Gondwana
This is the
sediments
that make
the rocks
building up
off the
coast of
Gondwana.
70 mya
Spreading
ridge in future
tasman sea
starts NZ
moving away
on its long
journey.
10 mya
NZ starts to
take shape.
Land mass is
large, one
island.
Tectonic
collisions are
similar today.
Research
How do we know that NZ was once past of
Gondwana?
What was the climate like?
What sort of life lived on Gondwana?
How long were the Southern continents together
before they separated?
What caused NZ to separate from Gondwana?
What are some species of plants and animals
whose ancestors were on NZ when it
separated?
Local features and geological
formations
Alpine fault and Wairau fault
The alpine fault branches into the Wairau fault
that passes through Marlborough.
It is a break in the Earth’s crust caused by the
collision of the Australian and Pacific plates.
Collision of tectonic plates causes mountain
building around the fault.
The Wairau fault divides Marlborough and is still
active.
The Wairau earthquake of 1848 caused
subsidence of 5 ft in the lower Wairau Valley and
was widely felt throughout the southern part of
the North Island.
The Sounds are flooded river valleys.
The alpine fault on the East of the
Alps
Marlborough Sounds - flooded valleys
When the strong tidal currents of Cook Strait flow through the narrow
entrances of the Marlborough Sounds, complex currents are
produced. Whirls and current paths are visible in this photograph,
taken from space. The waters seen here have different levels of
turbidity (sediment held in suspension).
Marlborough rocks
Many of the rocks that form Marlborough are
sedimentary rocks like greywacke, formed in the
oceans off the coast of Gondwana.
Schist is commonly found – a metamorphic rock
that makes up the mountains surrounding us. It
was formed deep in the Earth when the plates
were colliding.
We can see the rocks because colliding plates
has pushed them up out of the ocean and the
rocks covering them have been eroded away.
Marlborough Schist from Queen
Charlotte sounds – a metamorphic
rock.
Marine Fossils
Fossils can be found in many Marlborough
rocks.
When organisms died their skeletons were
fossilised in the rocks then uplifted and exposed.
Coastal areas such as Marlborough have only
been pushed up to become land in the last
50,000 years so we don’ have many old fossils.
Rich deposits of beautifully preserved
Pleistocene sea shell fossils can be found at
Motunau Beach (Marlborough). They are
evidence for shallow, sandy bottom seas.
Erosion in action
Weathering
Earth's surface is constantly being shaped and
reshaped by natural processes like earthquakes
and volcanic eruptions, weathering and erosion.
Weathering causes rocks at Earth's surface to
fragment, crack, crumble, or otherwise degrade
due to physical, chemical, or biological
interactions.
Because different kinds of rocks form in different
settings, they react differently when exposed to
temperature swings, moisture in the air, or
pressure changes.
Formation of a V-shaped valley
V-shaped valleys are found in the upper course
(mountainous) part of a river.
Vertical erosion creates a steep narrow gorge.
The sides of the gorge are made less steep by
the weathering creating a V shape.
Any material that falls from the valleys sides
usually rolls into the river below and when the
velocity of the river is fast enough the material is
transported away.
The animation below shows this process:
V shaped valley
Erosion
Erosion loosens and carries away rock debris formed by
weathering.
Without erosive agents, including water, wind, and
glaciers, rock debris would accumulate where it formed.
Moving water is the most potent erosive force on Earth.
Powered by the force of gravity, the world's rivers deliver
about 20 billion tons of loose rock fragments, or
sediment, to the oceans each year.
Moving air, or wind, is another important transporter of
sediment, especially in dry regions. When tiny sand
grains are lifted and carried by the wind, the wind also
becomes an erosive agent, capable of sculpting rocks
into a variety of shapes, as evidenced in the still images
Glacier
A glacier is a frozen flowing river that
moves slowly, retreating in summer and
growing in winter. (Franz Joseph)
Terraces
Terraces are produced by erosion. The
pink and white terraces of Rotorua
distroyed in the 1888 eruption of Mt
Tarawera
Moraines
A moraine is found at
the base of a glacier
where large rocks and
sediments (glacial
drift) are deposited
after being
transported by the
glacier
A moraine at the base
of the Southern Alps
A end moraine in Canada
Fiords
A long narrow inlet
with steep sides
created in a valley
that was created by
glacial activity.
The Southern
sounds are actually
fiords.
These areas were
once glaciated.
Fiordland
Rocks and the Rock Cycle
Sedimentary Rocks
Sedimentary – formed from eroded
sediments off other rocks that are washed
down into river, lakes and oceans,
deposited on the sea floor.
Pressure and chemicals cement them
together.
We see them when plate movements push
them up.
Eg, greywacke, limestone (fossils),
sandstone, mudstone, conglomerate.
Igneous Rocks
Harder rocks that form from magma that
solidifies.
Extrusive or volcanic form from lava that
comes out of Earth. Cool quick some small
crystals. Eg, scoria, pumice, obsidian
Intrusive or plutonic form from lava that
cools slowly inside crust – larger crystals.
Eg, granite.
Metamorphic Rocks
Any rock can change into a metamorphic
rock.
Formed by deep burial of rocks in the
crust.
Caused by intense heat and or pressure
Rocks recrystalise and become hard.
Often attractive, contain gems
Eg, pounamu, marble
Rock cycle
Interactive Rock Cycle Animation
All done
congratulations