1. Why does the Earth shake?L
To explain how earthquakes occur
To understand how to measure earthquakes
Why does the Earth shake?
Key terms: Plates, friction, Richter scale, Mercalli scale

2. When the Earth shakes…
Notice how people react, and how serious they take the event…

3. California USA: The Quake State
As you saw, the people of California take earthquakes very seriously. Many tremors (smaller earthquakes) hit the state every year. Why is this?
TASK
1.Read the sheet, then explain how earthquakes actually take place. Write a short account.
2.Model how an earthquake happens using props. You could use your hands, two tables or yourself and a friend.

4. Measuring Earthquakes
Earthquakes are measured in two ways:
The Richter scale measures the power
The Mercalli scale measures the damage

5. Richter Scale The Richter scale measures the power of the earthquake.
It goes from 1 to being little shaking, 10 being very violent shaking.
The highest ever recorded earthquake was 9.2 in Chile, South America in 1960
In order to work out how much shaking is going on, an instrument called a seismograph is needed.

6. A seismograph
Seismographs are sensitive instruments that measure shaking. Let’s build our own one!!

7. Building a seismograph
Get a pen and tie string around the end. This will act as the wire.
Mould a lump of Blue-tac around the middle of pen. This will act as the weight.
Dangle the pen by the end of the string over a piece of paper.
Get a friend to violently shake the table. What do you see happening on the paper? You have created a seismogram.

8. A seismogram
Once you have a seismogram like this one of an earthquake in the UK, you can work out the power of the quake and where it is on the Richter scale.

9. Mercalli Scale Measures the damage using descriptions levels from 1 to 12.
I. Felt by almost no one.
II. Felt by very few people.
III. Tremor noticed by many, but they often do not realise it is an earthquake.
IV. Felt indoors by many. Feels like a truck has struck the building.
V. Felt by everyone; many people are awakened. Swaying trees and poles may be observed.
VI. Felt by all; many people run outdoors. Furniture is moved.
VII. Everyone runs outdoors. Poorly built structures considerably damaged. Slight damage elsewhere.
VIII. Specially designed structures damaged slightly, others collapsed.
IX. All buildings considerably damaged, many shift off foundations. Noticeable cracks in the ground.
X. Many structures destroyed. Ground badly cracked.
XI. Almost all structures fall. Bridges wrecked.
XII. Total destruction. Waves seen on ground surfaces, objects are tumbled and tossed.
TASK Create your own picture scale of the Mercalli scale using the grid. You will use your scale to measure the Christchurch earthquake, New Zealand against the Mercalli scale.

10. Mercalli Scale

11. Christchurch Earthquake New Zealand