: Figure 2.20 The San Andreas Fault. Earthquakes occur here because the Pacific Plate and the North American Plate are sliding past each other
: Figure 2.21 Satellite view of the San Andreas Fault Measuring earthquakes
A person who studies earthquake activity is called a seismologist. A seismologist uses instruments called seismographs to measure tremors in the Earth’s crust.
The Richter scale, and more recently the Moment Magnitude Scale (Mw) are used to show the strength of an earthquake. The Richter scale ranges between 1 and 10. Each unit is ten times stronger than the one before. For example, an earthquake measuring 6 on the Richter scale is ten times stronger than one that measures 5.
Damage caused by earthquakes • There is loss of life. • Buildings are damaged or collapse. • Damage to electricity lines or gas pipelines may cause fires.
• Damage to sewers and water supplies may cause the spread of disease.
• Bridges, roads and railway lines are damaged, often making it difficult to get help into the area.
• Landslides and avalanches can be triggered, causing more death and destruction.
• When an earthquake occurs under the sea, water can be displaced, making a huge wave called a tsunami. This may eventually crash onto the coastline, causing devastation.
: Figure 2.23 Buildings ruined during an earthquake in Turkey in 2011
ACT VITY
Research the impact of a tsunami, such as the one in South-East Asia in 2004. Work in groups and answer the following questions: (a) What countries were affected? (b) What was the death toll? (c) How many people were left homeless? (d) What was life like for people living in these areas afterwards?
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:Figure 2.22 Seismographs measure tremors in the Earth’s crust
