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GCSE Geography Revision Topics: Tectonics

Structure of the earth
Tectonic Plates
Plate margins
Earthquake/Volcano distribution
Earthquakes: Kobe
Earthquakes: California
Consequences: how they respond
What might the examiner ask?


Tectonics:

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?

  1. What is crustal instability?
  2. What causes plate movement?
  3. Describe a particular plate margin with the aid of drawings
  4. What effect - earthquake/volcano?
  5. Why do earthquakes occur in Japan/California?
  6. How do countries respond to earthquakes?


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