1.16 Science Event:Earthquakes in Christchurch

Achievement Standard Science 90955: Investigate an astronomical or Earth science event

Resource reference: Science 1.16B v2Resource title: Earthquakes in Christchurch Credits: 4

Achievement Standard

Achievement Achievement with Merit

Achievement with Excellence

Investigate an astronomical or Earth science event.

Investigate, in-depth, an astronomical or Earth science event.

Investigate, comprehensively, an astronomical or Earth science event.

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?

Focus Questions

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The thin layer of solid rock which covers the Earth is called the crust.

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?

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Under this is the mantle.

The middle of this is molten - so the upper mantle and crust float on this.

What does the Earths interior look like?

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The inner layer is the core, which is a solid core surrounded by molten rock.

What does 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.

How do we know what the Earths interior look like?

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SJ

The earth’s crust is divided into different sized pieces called plates. They fit together to cover the earth.

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 Gaz

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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.

Evidence for Plate Tectonics

Plate Tectonics

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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

Plate Movement

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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Divergent Boundary

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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

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.

Convergent Boundary

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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.

Transform fault Boundary

Aerial view of the San Andreas fault slicing through the Carrizo Plain in the Temblor Range

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Fault seen through plantation

Transform fault Boundary

Plate Boundary Summary

Divergent Boundary

Convergent Boundary

Transform plate Boundary

Plate Boundary Summary

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.

What causes earthquakes

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.

As plates move the strain causes brittle rock to crackThese cracks, called faults, are often weak zones where more movement

or cracking may occurConstant movement of plates causes pressure to build up at faults, and at

the boundaries of the platesIf there is a sudden slippage of rock, this pressure is released quickly and

an earthquake occurs

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What causes earthquakes

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

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.

Earthquake waves

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

New Zealand is on the top of two plates moving with transverse motion.

Why Does NZ have so many earthquakes?