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Earthquakes and Earths interior

Chpt 7 notes
by

Matthew Lewis

on 26 January 2012

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Transcript of Earthquakes and Earths interior

Earthquakes
and
Earths Interior
What are Earthquakes?
An Earthquake is a vibration of the earth produced by the of energy within the crust.
rapid release
What Causes an Earthquake?
Earthquakes are caused by slippage along a break in the crust called a
Fault
Why do rocks slip and break?
Rocks slip and break due to the build-up of energy stored in the rock
Think about when you break a pencil or a ruler
As rocks move inside the earth they deform
Land starts to move in opposite directions along the fault
Land deforms as energy is built up
After earthquake the land is offset
This process is called
Elastic Rebound
What are the parts of an Earthquake?
1.Focus
The point underground where the earthquake starts
2. Epicenter -
The point on the earths surface directly above the focus of an earthquake
What are Seismic Waves?
Earthquakes produce two types of waves
Body Waves:


Surface Waves:
Waves that travel through the interior of the earth
Seismic waves created when body waves reach the surface of the earth
How do Seimic waves move the ground?
are known as push-pull waves and travel in the direction of the wave motion
Shake the ground perpendicular to the wave motion
Body waves move in two different ways
P waves:



S waves:
Surface waves move the ground in all directions (up/down and Side to side) and do the most damage
P waves move faster than S waves which move faster than Surface Waves
P > S > Surface
How do Scientists record Earthquakes?
Scientists use Seismographs
Seismographs use a suspended weight attached to a base that is attached to bedrock
How do scientists measure Earthquakes?
Scientists use 3 methods:
1 - Richter Scale: based on the amount of ground movement

2 - Moment Magnitude: based on the amount of energy released by the earthquake

3 - Modified Mercalli Scale: Based off of the amount of damage done to structures
Since seismic waves move at different speeds the seismograph records the movements of the earth in a distinct pattern
An early Chinese Seismograph
How do Scientists locate earthquakes?
Scientists use readings from seismograph stations around the world
Example
The process of finding the epicenter of an earthquake with at least 3 seismograph readings is called
Triangulation
What other dangers are associated with earthquakes besides the ground Shaking?
1. Liquefaction - when soil with a high water content is subjected to seismic shaking it has a chance to behave more like a liquid.
buildings may sink or settle into the ground

pipes and sewer lines may rise to the surface

2. Mass Movements - Earthquakes can trigger landslides and other mass movements in areas that are stable
3. Tsunami - The ground moving underwater or ground falling into the water can cause a tsunami
Earths Interior is classified in two ways:
By Composition and Physical Properties
Layers by Composition
Oceanic Crust is more dense than Continental crust
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