Year 8 Science · Unit 3 · Lesson 22
Apply Worksheet
Learning Goals
Order the steps
Number the events from 1 to 8 to show the correct order. Event 1 = what happens first.
| Order | Event |
|---|---|
| Surface waves travel along Earth's surface, they are slowest but cause the greatest shaking of buildings. | |
| Seismologists at three or more stations use the different P–S arrival times to triangulate the epicentre's location. | |
| Tectonic plates slip along a fault, releasing stored elastic energy in seconds. | |
| S-waves (shear waves) travel outward through solid rock and arrive at seismograph stations after the P-waves. | |
| Seismograph stations record the arrival times of each wave type, P-waves first, then S-waves, then surface waves. | |
| The focus is identified as the underground origin point; the epicentre is the surface point directly above it. | |
| P-waves (compression waves) radiate outward from the focus in all directions, they are the first to arrive at distant stations. | |
| Seismic waves are generated and begin travelling outward through Earth from the focus. |
Real-world context
On 28 December 1989, a magnitude 5.6 earthquake struck Newcastle, NSW, Australia's deadliest earthquake of the 20th century. It killed 13 people, injured 160, and caused approximately $4 billion in damage. Before 1989, Australian building codes did not require earthquake-resistant design in NSW, because the continent was considered seismically "safe" due to its distance from major plate boundaries.
(a) Why are Australian cities generally considered "low risk" for earthquakes? Use your knowledge of plate tectonics to explain why the risk is not zero.
(b) The Newcastle earthquake was only magnitude 5.6, considered "moderate", yet it was more devastating than many larger earthquakes in other countries. Suggest two reasons why the damage was so severe for this magnitude.
(c) What warning systems or building codes could reduce harm in a future moderate Australian earthquake? Describe at least two specific measures and explain how each would help.
1. A seismograph records P-waves at 10:00:00 am and S-waves at 10:00:25 am. Explain what the 25-second gap between these arrivals tells a seismologist.
2. Which type of seismic wave causes the most building damage during an earthquake? Explain why this wave type is so destructive compared to P-waves.
Wrap Up
In one sentence, what was the main idea of this lesson?