Sunday, February 19, 2012

Earthquake Notes (2)

 Formation and features

When plates fracture/slip they form seismic waves (vibrations) into the ground, these vibrations can be classified into to primary, secondary and surface waves.
Primary waves:
-They are the fastest moving waves
-They can pass through solids, liquids and gases easily
-These waves typically arrive at the surface as an abrupt thud.
Secondary waves:
-They move slower than primary waves,
-Can only pass through solids.
-As S waves move, they displace rock particles outward,. This results in the first period of rolling associated with earthquakes.
-They only travel through solid material, and so are stopped at the liquid layer in the Earth's core.
Surface waves:
-Move along the surface of the Earth.
-Surface waves cause the most damage. They move up and down the surface of the Earth,
-Surface waves are the slowest moving of all waves,. So the most intense shaking usually comes at the end of an earthquake.


Epicenter: The point of the earth’s surface vertically above the focus of an earthquake

Fault Line: A separation/crack between two tectonic plates, an earthquake occur if the plates move against each other.

Focus: The point where the earthquake occurs, they can be divided into shallow and deep focus

Shallow focus: Occurs near the surface of the earth, causes moderate to major damage
Deep focus: Occurs far from the earth’s surface, causes little to no damage

Seismic Waves: Vibrations that travel through the earth due to the cause of earthquakes, these waves can be classified into primary, secondary and surface waves.

How are earthquakes measured?
The ‘strength’ of an earthquake is known as magnitude. Magnitude is a measure of the amount of energy released by an earthquake. The magnitude of an earthquake is measured using the Richter scale. A seismometer (machine with an arm that moves with the vibrations of earth) detects the vibrations caused by an earthquake. It plots these vibrations on a seismograph. The Richter scale doesn’t have an upper limit and it is logarithmic. Major earthquakes are above 5. The Mercalli scale is used to indicate the intensity of an earthquake. It classifies the effects of an earthquake on a scale using Roman numerals from I to XII (1 to 12, from rarely ever felt by people to disastrous, with almost total destruction). The number on the scale is obtained by making a judgement and observation, it is not measured by a machine.

The Richter scale is more mathematical, and tells you how much energy was released. However, it is not that good in telling what damage happened. The Mercalli scale tells you the damage that occurred, but is not as scientific, and is subject to people’s views of the event which may differ.

Primary/Secondary effects Of An Earthquake

Primary effects
- Natural habitats destroyed by landslides caused by the earthquake
- Homes destroyed or collapsed
- People killed or buried in the rubbles
-  Shops collapsed
- Roads severely damaged or destroyed

Secondary effects
- Loss of habitat, leaving animals homeless
- People will not have any shelter
- Family members of the victim will mourn over their deaths
- Because shops are destroyed, the people will have to face starvation due to the fact that it wont be able to provide food.
- Roads that are severely damage wont be able to be used, limiting the movement of emergency units and emergency supply.

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