Describe the nature of Earthquakes and Tsunami.

The Nature of Earthquakes

Lesson Objectives

• Be able to identify an earthquake focus and its epicenter.
• Identify earthquake zones and what makes some regions prone to earthquakes.
• Compare the characteristics of the different types of seismic waves.
• Describe how tsunamis are caused by earthquakes, particularly using the 2004 Boxing Day Tsunami as an example.

Vocabulary

• amplitude
• body waves
• crest
• earthquake
• elastic rebound theory
• focus
• seismology
• surface waves
• trough
• tsunami
• wavelength

Introduction

An earthquake is sudden ground movement caused by the sudden release of energy stored in rocks. Earthquakes happen when so much stress builds up in the rocks that the rocks rupture. The energy is transmitted by seismic waves. Each year there are more than 150,000 earthquakes strong enough to be felt by people and 900,000 recorded by seismometers!

Causes of Earthquakes

The description of how earthquakes occur is called elastic rebound theory (Figure below).

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