# Earthquakes

AQA Geography B

Hostile World Exam Notes

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## STRUCTURE OF THE EARTH

The Earth has four layers - inner core, outer core, mantle and crust

Core - iron and nickel

- hot and dense

- outer core is molten, inner core is solid

Mantle - Semi-molten liquid

- Heat from the core creates convection currents

Crust - Thin layer of rock

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## PLATE TECTONICS AND CONTINENTAL DRIFT

The crust is made up of plates

The convection currents in the mantle cause continental drift

<--These are some of the plates

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## LOCATION OF EARTHQUAKES

Longitude - How east or west you are

Latitude - How north or south you are

Earthquakes occur at plate boundaries in linear patterns

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## WHAT HAPPENS AT PLATE BOUNDARIES

Constructive Boundary

Where plates are moving apart

Magma rises in the gap and can escape easily - so eruptions are quite gentle

Destructive Boundary

Where an oceanic plate moves towards and under a continental plate - it gets subducted

The oceanic crust then turns to magma because of the heat and pressure

Get both earthquakes and volcanoes

Conservative Boundary

Where plates move side by side - opposite directions or same direction

Earthquakes occur is the plates get stuck then suddenly 'jerk' past each other

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## WHAT HAPPENS IN AN EARTHQUAKE?

Definitions...

Earthquake – A sudden movement within the earth’s surface, usually close to a plate boundary

Magnitude – The amount of energy that is given out during an earthquake

Focus – This is the point underground where the earth’s plates have moved

Epicentre – The point on the surface directly above the focus

Seismic waves – These are waves of force that travel through the earth.

Seismometer –An instrument used to measure the movement of the earth’s surface. A seismometer records the vibrations from earthquakes.

Seismograph – A graph produced by data collected from the seismometer - shows the shaking of the earth

Aftershocks – Smaller earthquakes formed as the crust around the displaced fault adjusts to the effects of the main shock.

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## PRIMARY AND SECONDARY EFFECTS

Primary Effects

Happen straight away directly from the ground shaking

• Buildings collapse, windows shatter, bridges collapse

Secondary Effects

Happen as a result of the primary effects.

• Fires (from ruptured gas mains), disease, dirty water, buildings collapse due to liquefaction (explained below)

Liquefaction

When soft sediment behaves like quicksand during an earthquake. This is because the shaking brings water to the surface which buildings sink into.

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## COMPARING THE EFFECTS

LEDC...

• Not much money for equipment and supplies
• Cities are densely populated - often shanty towns
• Poor construction
• Communications systems are underdeveloped

MEDC...

• Emergency services are well funded
• Lots of money for researching and monitoring
• Old buildings can be retrofitted
• Buildings can be quake-proofed
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## LIMITING THE EFFECTS

Human built structures...

• Retrofitting
• Shorter buildings
• Strong materials - wood and steel
• Base isolators - isolating the base of the building from the earth's movements
• Building codes and regulations

However, most of these are only available for MEDC's so LEDC's use appropriate technology (technology designed with consideration of the community it is intended for)

For example: bamboo houses

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## PREPARING FOR EARTHQUAKES

What people can do before...

• Store bottled water and food
• Earthquake drills
• Reinforce buildings

What people can do after...

• Be prepared for aftershocks
• Stay away from damaged areas
• Donate
• Search and rescue
• Rebuilding
• Monitor in case of tsunamis
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