# Tectonic Hazards Revision

• Created by: Théa
• Created on: 10-06-13 19:01

## Earthquakes

-Earthquake = a sudden movement of the earth's crust caused by the release of stress built up along faults.

-Fault = an area of weakness in the earth's crust.

-Earthquakes occur mainly on plate boundaries that are moving towards or past each other (Convergent or Transform).

-As the plates move, friction locks them together.

-Over many years, pressure builds up until eventually the rocks snap along a weak area called a fault line.

-The stored energy is released and it travels outwards as seismic waves.

-These seismic waves or shock waves, cause the earth's crust to shake up and down, and side to side, causing an earthquake.

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## Earthquakes

-Focus = is the point at which the rock moves. The seismic waves start at the focus.

-Epicentre = is directly above the focus, on the Earth's surface.

-It is very difficult to predict earthquakes, however you can predict what level it will be on the Richter Scale and a very vague time it could occur, but not a specific date and time.

-The magnitude of an earthquake, usually expressed by the Richter Scale, is a measure of the amplitude of seismic waves.

-The Richter Scale is relatively old fashioned, however.

0-2 = Not felt by people

5-6 = Walls crack and furniture moves

8-Up = Total destruction

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## Earthquakes

-Modified Mercalli Scale is also a way of classifying earthquakes and demonstrates what it felt like for a person, during the earthquakes, making it subjective.

-The moment magnitude of an earthquake is a measure of the amount of energy released, measured with seismograph readings.

-P and S waves are two different types of seismic wave, which are used to calculate where the epicentre of the earthquakes was.

-The largest earthquake in history was in Valdivia, Chile. It happened on the 22nd of May 1960 and was 9.5 on the Richter Scale.

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## Factors affecting the damage of earthquakes

-Physical Landscape

-Time of day

-Education of people

-Size of earthquakes

-Building design and structure

-Emergency services

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## How can we limit earthquake damage?

Plan:

-Enforce regulations to make some buildings earthquake proof.

-Make an emergency plan

-Advise people to plan for an earthquake (eg. turn off gas, find a "safe" place, etc.)

-Organise regular 'earthquake practices' for offices and schools

-For example: The Californian Government created the "Drop. Cover. Hold On." campaign.

Buildings:

-Make sure buildings have overlapping bricks

-Ensure buildings like skyscrapers have a wide base, deep foundations and strong lintels (window frames)

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## How can we limit earthquake damage?

Predict:

-Foreshocks may occur before the main earthquake

-A tilt meter can check movement in the rocks

-Animals can act strangely before an earthquake

-Water cracks can rise before an earthquake, due to cracks in the rocks

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