Earthquakes

Learning Objectives To understand: what earthquakes are what causes them where they are located ways of recording and measuring earthquakes the effects of earthquakes

(The Concise Oxford Dictionary of Geography, 1992) What are earthquakes? Earthquakes are ‘a sudden and violent movement, or fracture, within the earth followed by the series of shocks resulting from this fracture’. (The Concise Oxford Dictionary of Geography, 1992)

What causes Earthquakes? Earthquakes happen mainly along the boundaries of the Earth’s plates. At plate boundaries two separate parts of the Earth’s crust either move towards, or past each other. As plates rub against each other friction can lock them together.

What causes Earthquakes? Over time pressure builds up until eventually it becomes so great the rock slips suddenly along a weak area called a fault line. The focus is the place underground where the rock actually slips. The place at the surface directly above the focus is called the epicentre.

What causes Earthquakes? As the built up energy is released it travels outwards as shockwaves which are known as seismic waves. These seismic waves cause the Earth crust to shake and tremor which can cause a lot of damage on the earth surface. As the seismic waves move through the crust they lose energy so less damage is caused further away from the epicentre.

Task Who wants to have a go at labelling where: a) focus b) fault line c) epicentre d) seismic waves are on the diagram on the white board? Now complete the diagram for the handout you have been given….

Fault line Seismic waves Epicentre Earthquake Focus

Can you name the plate boundaries? Earthquakes can occur at the 4 main plate boundaries but the most powerful earthquakes are normally at and boundaries. DESTRUCTIVE DESTRUCTIVE CONSERVATIVE CONSERVATIVE

Location of Earthquakes Earthquakes are mainly found in long narrow belts across the earths surface following the plate boundaries. Due to the friction at plate boundaries these are also areas where volcanoes are often located. The map on the next slide illustrates the location of earthquake activity…..

Task On the map on your handout draw and name the major earthquakes in the world. Use page 27 of Interactions textbook to help you.

Recording and measuring Earthquakes Seismic waves (shockwaves) from earthquakes are recorded by scientists on seismometers. Seismic waves from the other side of the world can be picked up (detected) by seismometers. A simplified drawing of a seismometer. Earthquake strength can be measured using 2 different scales – the Mercalli scale and the Richter scale.

The Mercalli Scale The Mercalli scale measures the amount of damage done by the earthquake in a certain area. The Mercalli scale ranges from 1 to 12 (1=least damage, 12 =most damage). Look at your handout can you put the pictures on the following slide in order? (some have been done for you)

Can you put these pictures in order?

Let’s see if you got it right... 1 5 9 2 6 10 3 7 11 4 8 12

Richter Scale Only detected by instruments Faint tremor, little damage Distinct shaking Major earthquake Widespread destruction Possible effects Richter Scale Richter scale is used to measure the scale (magnitude) of earthquakes from 0 to 10, of the amount of energy released. It is a logarithmic scale which means that a size ‘7’ on the scale is 10 times larger than a size ‘6’. A size ‘7’ is 100 times larger than a size ‘5’ (10 x 10 = 100). The largest earthquake ever recorded was in Chile (1960). It measured 8.9 on the Richter Scale.

Lets see by clicking the information button how much the screen would shake during an earthquake depending on its size, using the Richter Scale.

The effects of earthquakes Primary effects are the immediate effects caused directly by the earthquake. These include: Damage or collapse buildings Damage to other infrastructure (e.g. roads, bridges, railway lines) Falling objects (signs or glass from buildings) Injury or death to Human Life

The effects of earthquakes Secondary effects are indirect effects and problems faced after an earthquake. These include: Fires (caused by burst gas pipes) Lack of food and water Spread of disease (cholera and typhoid) Tsunami (huge waves of up to 30 metres high and travelling up to 500km hour)

Task Discuss with a partner the following photographs taken after an earthquake and decide what effects they are trying to show. Then decide whether this effect is primary or secondary.

1. Fire 2. Collapse buildings 3. Collapse bridge 4. Damaged railway line

5. Tsunami 6. Falling objects 7. Communication lines stopped 8. Spread of disease

Copy and complete the table Effect shown Primary Secondary 1. Fire 2. Collapse buildings 3. Collapse bridge 4. Damaged railway line 5. Tsunami 6. Falling objects 7. Communication lines stopped 8. Disease