LESSON 14.6 What are earthquakes?
LEARNING INTENTION By the end of this lesson, you should be able to: • identify the processes that produce earthquakes • define the key terms earthquake , epicentre , fault plane , focus , seismic waves , primary waves and secondary waves • understand how earthquakes are measured.
Tune in Examine FIGURE1 , a diagram explaining what occurs during an earthquake.
FIGURE1 What happens during an earthquake?
Direction of movement along fault
Fissures
Epicentre
Soft ground under lake or sea
Seismic waves
Bedrock
Focus
1. Discuss what you think might be the difference between the focus and epicentre of an earthquake. 2. What factors might contribute to some earthquakes resulting in a lot of damage whereas others result in little damage?
14.6.1 Earthquakes An earthquake is the sudden shaking of the ground caused by the passage of seismic waves through the Earth’s crust. Earthquakes occur every day somewhere on the planet, usually on or near the boundaries of tectonic plates. There is a strong relationship between the location of plate boundaries and the occurrence of earthquakes (see FIGURE2 ). Weaknesses and cracks in the Earth’s crust near plate boundaries are called faults (or the fault plane ). An earthquake is usually a sudden movement of the layers of rock at these faults.
380 Jacaranda Humanities Alive 8 Victorian Curriculum Third Edition
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