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Plate Tectonics and Associated Hazards

Causes of Earthquakes:
the sudden release of pressure caused by a slow build up of pressure within the rocks that
results in intense shaking

Focus: The point at which pressure release occurs within the trust
Epicentre: point immediately above that on the Earth's surface and…

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The majority of earthquakes occur along plate boundaries with the most powerful at
destructive margins.
At conservative margins the boundary is marked by a fault, which movement along
produces and earth quake. E.g. the San Andreas fault, California which represent
the boundary between the North American and Pacific plate.…

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Magnitude and frequency:
Magnitude of earthquakes is measured on two scales.
The Richter scale:
A logarithmic scale ­ (an event measured at 7 has an amplituded of sesmic waves
ten times greater than one measured at 6)
Goes from 110 but rarely goes into 9s
The Mercalli scale
Measures the…

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Effects of earthquakes
Primary effects:
Ground shaking ­ the severity depends upon the magnitude of the earthquake, the distance
from the epicentre, local geological conditions and rock type.

Secondary effects:
Soil Liquefaction when violently shaken soils with a high water content lose their
mechanical strength and start to behave like…


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