Natural Disasters - Earthquakes Topic 5 – Lesson 1

Introduction On December 28 th 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 infoClick here for more info Look at page 24 HSC Spotlight Text to other Australian recorded quakes.

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.

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.

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.

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.

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.

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.

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).

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.

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 HSC Spotlight Text.

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?

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.

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

Review Earthquakes 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).

Homework Read pages HSC Spotlight Text Update electronic vocabulary Complete DOT Point 4.3, 4.4 and 4.6

Natural Disasters-Earthquakes Topic 5-Lesson 2

Review Earthquakes 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).

Plate Tectonics and Earthquakes Around 95% of earthquakes occur at plate boundaries. Studying the locations of earthquakes has helped to determine these plate boundaries.

Plate Tectonics and Earthquakes Divergent plate boundaries tend to produce low magnitude- shallow (0-15km deep) earthquakes. These happen along mid ocean ridges and are produced by normal faulting.

Plate Tectonics and Earthquakes Transform plate boundaries also produce shallow earthquakes but the movement is horizontal which leads to quite destructive results when close to populated areas.

Plate Tectonics and Earthquakes Convergent 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.

Plate Tectonics and Earthquakes So 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.

Plate Tectonics and Earthquakes 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. Because the focus is generally shallow they can be very devastating when close to populated areas.

Earthquake Hazards Most 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.

Earthquake Hazards The 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.

Earthquake Hazards Structures 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.

Earthquake Hazards Because 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?

Earthquake Hazards Another 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?

Earthquake Hazards Fires 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.

Earthquake Hazards Earthquakes 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.

Review Around 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.

Homework Read pages HSC Spotlight Text Update Electronic Vocabulary Complete DOT Point 4.1, 4.2.2, 4.4 and 4.5

Natural Disasters-Earthquakes Topic 5-Lesson 3

Activity Research the 2004 Indonesian Tsumani and complete DOT Point 4.10 together

Natural Disasters-Earthquakes Topic 5-Lesson 4

Review Around 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.

Predicting Earthquakes Humans are unable to control earthquakes. All we can do is plan for them and prepare. Activity Read and discuss pages HSC Spotlight Text Complete Activity 1.17 pg HSC Spotlight Text Complete DOT Point 4.11 together

Homework Update electronic vocabulary from in class reading Complete ‘To Think About’ page HSC Spotlight Text