Natural Disasters - Earthquakes Topic 5 – Lesson 1.

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Natural Disasters - Earthquakes Topic 5 – Lesson 1

Transcript of Natural Disasters - Earthquakes Topic 5 – Lesson 1.

Page 1: Natural Disasters - Earthquakes Topic 5 – Lesson 1.

Natural Disasters - Earthquakes

Topic 5 – Lesson 1

Page 2: Natural Disasters - Earthquakes Topic 5 – Lesson 1.

Introduction On December 28th 1989 a moderate earthquake

that measured 5.6 on the Richter scale devastated Newcastle. 13 people were killed. The quake struck without any warning in a place considered to be low risk. Click here for more info

Look at page 24 HSC Spotlight Text to other Australian recorded quakes.

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Earthquakes and how they are measured

Earthquakes are uncommon in Australia because the continent is in the middle of a plate. Earthquakes happen along faults/plate boundaries. Forces push two sides of a fault in different directions which causes the ground to shake.

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Earthquakes and how they are measured

Sometimes the movement is slow while other times very quick. Friction between the rocks on either side allows for little movement and elastic potential energy is stored. When the elastic limit is reached, the fault moves. The movement may be a series of small jerks or one giant slip.

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Earthquakes and how they are measured

The location beneath the surface where this movement takes place is called the focus. It’s from this point the stored energy is released and travel outward in all directions. The point on the surface of the Earth directly above the focus is called the epicentre.

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Earthquakes and how they are measured

The waves produced by earthquakes are called seismic waves and they are measured by a seismograph. A large mass is suspended in a way that allows it to stay stationary as the ground shakes.

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Earthquakes and how they are measured

The recording drum moved with the shaking ground recording a pattern which is called a seismogram. The first part of a seismogram records the P-Waves (Primary). These are compression waves that cause minor tremors.

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Earthquakes and how they are measured

The next part of a seismogram is the S-Waves (Secondary). These are transverse waves where particles move at right angles to the direction of the wave. This is how water waves travel.

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Earthquakes and how they are measured

Scientists measure these P and S waves as they travel through the Earth to determine it’s internal structure (Mantle, Outer Core and Inner Core).

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Earthquakes and how they are measured

The next waves to arrive are the those that travel over the Earth’s surface, L-Waves (Long). Some L-Waves shake from side to side and cause lots of damage because of their greater amplitude.

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Earthquakes and how they are measured

Other L-Waves are like ocean waves which roll across Earth’s surface. These aren’t as destructive because they move vertically and buildings can stand being raised and lowered.

See diagrams on pages 36-37 HSC Spotlight Text.

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Earthquakes and how they are measured

The difference in the time of arrival of P and S waves can be used to plot the distance of seismic activity from seismic stations. How can scientists use this data to infer where an earthquake happened?

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Earthquakes and how they are measured

If you have 3 stations which recorded a quake , you can then use the distance registered at each station to calculate a radius and draw circles around each station. Where the three meet is the epicentre of the earthquake! See figure 1.35 pg 37 HSC Spotlight Text.

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Earthquakes and how they are measured

The Richter scale measures the energy released during an earthquake. Amplitude and distance are used to calculate this. See Figure 1.36 pg 38 HSC Spotlight Text

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ReviewEarthquakes happen along faults/plate boundaries.

Forces push two sides of a fault in different directions which causes the ground to shake.

The location beneath the surface where this movement takes place is called the focus.

The waves produced by earthquakes are called seismic waves and they are measured by a seismograph.

The recording drum moved with the shaking ground recording a pattern which is called a seismogram.

Scientists measure these P and S waves as they travel through the Earth to determine it’s internal structure (Mantle, Outer Core and Inner Core).

Page 16: Natural Disasters - Earthquakes Topic 5 – Lesson 1.

HomeworkRead pages 35-38 HSC Spotlight TextUpdate electronic vocabularyComplete DOT Point 4.3, 4.4 and 4.6

Page 17: Natural Disasters - Earthquakes Topic 5 – Lesson 1.

Natural Disasters-Earthquakes

Topic 5-Lesson 2

Page 18: Natural Disasters - Earthquakes Topic 5 – Lesson 1.

ReviewEarthquakes happen along faults/plate boundaries.

Forces push two sides of a fault in different directions which causes the ground to shake.

The location beneath the surface where this movement takes place is called the focus.

The waves produced by earthquakes are called seismic waves and they are measured by a seismograph.

The recording drum moved with the shaking ground recording a pattern which is called a seismogram.

Scientists measure these P and S waves as they travel through the Earth to determine it’s internal structure (Mantle, Outer Core and Inner Core).

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Plate Tectonics and EarthquakesAround 95% of

earthquakes occur at plate boundaries. Studying the locations of earthquakes has helped to determine these plate boundaries.

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Plate Tectonics and EarthquakesDivergent plate boundaries tend to produce

low magnitude-shallow (0-15km deep) earthquakes. These happen along mid ocean ridges and are produced by normal faulting.

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Plate Tectonics and EarthquakesTransform plate

boundaries also produce shallow earthquakes but the movement is horizontal which leads to quite destructive results when close to populated areas.

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Plate Tectonics and EarthquakesConvergent plate boundaries produce the

mot destructive earthquakes which can be shallow, intermediate or deep (up to 670km). They indicate the path of subducted crustal plates into the mantle.

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Plate Tectonics and EarthquakesSo what kind of quake hit Newcastle in

1989? Because we are located in the middle of a plate we are prone to intraplate earthquakes. These are different and poorly understood. Only about 5% of earthquake activity is within the centre of stable plates.

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Plate Tectonics and EarthquakesIntraplate earthquakes

are very difficult to predict and are best explained by being the cause of stresses and strains of the crustal plates as they move along the asthenosphere. Because the focus is generally shallow they can be very devastating when close to populated areas.

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Earthquake HazardsMost earthquakes are small however more

than 900 each year result in damage and sometimes death. The acceleration produced by shaking can be more than that of gravity. This can cause buildings to collapse and knock people off their feet.

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Earthquake HazardsThe ground can rupture and move both

horizontally and vertically resulting in cracks and small cliffs. Some buildings are designed to withstand shaking but not ruptures in the ground. Roads are fractured and bridges can collapse.

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Earthquake HazardsStructures all have something called a

natural frequency. They will naturally vibrate. If an external frequency matches this natural frequency the structure will resonate and shake violently.

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Earthquake HazardsBecause of this architects must think very

carefully about the materials they use to build structures. Do you think everyone considers this when building? What about people in third world countries? What do you think the effects of this may be?

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Earthquake HazardsAnother devastating effect of an

earthquake is that it can liquefy water-saturated alluvium, mud and silt. When this happens, buildings sink and buried tanks and pipes rise. How do you think this might effect emergency crews?

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Earthquake HazardsFires can be a

major hazard. Why do you think this is true? Most of the damage during the 1906 San Francisco earthquake was caused by fire because there was no water to put them out.

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Earthquake HazardsEarthquakes can also cause landslides and

tsunamis which can have very devastating effects. Earthquakes can create waves that travel up to 800km/h and reach heights of 20 metres. It was an earthquake which generated the Indonesian Tsunami in 2004 which resulted in nearly 230,000 deaths.

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ReviewAround 95% of earthquakes occur at plate

boundaries.Divergent plate boundaries tend to produce low

magnitude-shallow (0-15km deep) earthquakes.Transform plate boundaries also produce shallow

earthquakes but the movement is horizontal which leads to quite destructive results when close to populated areas.

Convergent plate boundaries produce the mot destructive earthquakes which can be shallow, intermediate or deep (up to 670km).

Intraplate earthquakes are very difficult to predict and are best explained by being the cause of stresses and strains of the crustal plates as they move along the asthenosphere.

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HomeworkRead pages 39-41 HSC Spotlight TextUpdate Electronic VocabularyComplete DOT Point 4.1, 4.2.2, 4.4 and 4.5

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Natural Disasters-Earthquakes

Topic 5-Lesson 3

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ActivityResearch the 2004 Indonesian Tsumani and

complete DOT Point 4.10 together

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Natural Disasters-Earthquakes

Topic 5-Lesson 4

Page 37: Natural Disasters - Earthquakes Topic 5 – Lesson 1.

ReviewAround 95% of earthquakes occur at plate

boundaries.Divergent plate boundaries tend to produce low

magnitude-shallow (0-15km deep) earthquakes.Transform plate boundaries also produce shallow

earthquakes but the movement is horizontal which leads to quite destructive results when close to populated areas.

Convergent plate boundaries produce the mot destructive earthquakes which can be shallow, intermediate or deep (up to 670km).

Intraplate earthquakes are very difficult to predict and are best explained by being the cause of stresses and strains of the crustal plates as they move along the asthenosphere.

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Predicting EarthquakesHumans are unable to control earthquakes.

All we can do is plan for them and prepare.

ActivityRead and discuss pages 41-43 HSC

Spotlight Text Complete Activity 1.17 pg 43-44 HSC

Spotlight TextComplete DOT Point 4.11 together

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HomeworkUpdate electronic vocabulary from in class

readingComplete ‘To Think About’ page 44-46 HSC

Spotlight Text