Structure of the earth
The earth is split into 4 main sections:
Inner Core - Centre of the earth
Outer Core
Mantel
Crust
Tectonic Plates
The earth's crust is divided into 12 large sections called tectonic plates. There are two types of plates - continental and oceanic. Continental plates contain the world's landmasses. They are older, lighter and thicker than oceanic plates.
Plates move as a result of convection currents in the mantel.
Plate margins
|
Margin
|
Description
|
Hazard or feature
|
Example
|
Case Study
|
| Destructive |
Where an oceanic plate moves towards a continental plate. Because the oceanic plate is heavier it subducts under the continental plate. |
Volcanoes and earthquakes. Fold mountains |
Pacific plate, Philippines plate & Eurasian plate |
Kobe Earthquake
Eruption of Mount Pinatubo |
| Conservative |
Where two plates slide past each other. |
Earthquakes |
Juan de Fuca Plate & North American Plate |
California Earthquake |
| Collision |
Where two continental plates move towards each other. |
Fold mountains |
Indo-Australian plate & Eurasian Plate |
Construction of the Himalayan Mountains |
| Constructive |
Where two plate move away from each other. |
Volcanoes and earthquakes |
Eurasian & North American Plate |
Formation of Iceland and West Indies etc |
Earthquake/Volcano distribution
Earthquakes and volcanoes occur along plate boundaries. Over half of the world's volcanoes and earthquakes occur along the Pacific Ring of Fire. This is a destructive plate margin running around the rim of the Pacific Ocean.
Earthquakes: Kobe
What?
Earthquake measuring 7.2 on the Richter Scale. The earthquake lasted 20 seconds.
Where?
Epicentre was under Awaji Island in Osaka Bay, close to the port city of Kobe, Japan.
When?
17th Jan 1995 at 5.46am.
Why?
Located on a destructive plate margin. Pacific Plate and the Eurasian Plate
So What?
250 000 people left homeless
5000 people died mostly as a result of fires caused by ruptured gas mains.
25 000 injured
Older buildings were worst hit.
Total cost est. $100 billion
Earthquakes: California
What?
Earthquake measuring 6.9 on the Richter Scale.
Where?
San Francisco, California, USA
When?
17th October 1989 at 5.04pm
Why?
Located on a conservative plate margin. Juan de Fuca Plate & North American Plate
So What?
2 000 people left homeless
67 people died
3000 injured
Older buildings were worst hit.
Total cost est. over $7 billion
Consequences: how they respond
In rich countries (MEDCs) like Japan planners attempt to reduce the impact of earthquakes by including seismic isolators in their buildings. Gas mains can be cut off immediately. People participate in earthquake drills once a year. This is damage limitation.
In LEDCs they cannot afford to take such measures. This is one reason why the impact of earthquakes in LEDCs is greater.
What might the examiner ask?
- What is crustal instability?
- What causes plate movement?
- Describe a particular plate margin with the aid of drawings
- What effect - earthquake/volcano?
- Why do earthquakes occur in Japan/California?
- How do countries respond to earthquakes?
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