Theme 3: Nat Haz (Tectonic) - General Revision

Tectonics

Structure of the earth
The earth is split into 4 main sections:

Inner Core – Centre of the earth
Outer Core
Mantle
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
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
Pacific 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.

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.