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Earthquakes. Earthquakes are natural vibrations of the ground, caused by: Fractures in earths crust Volcanic eruptions.

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Presentation on theme: "Earthquakes. Earthquakes are natural vibrations of the ground, caused by: Fractures in earths crust Volcanic eruptions."— Presentation transcript:

1 Earthquakes

2 Earthquakes are natural vibrations of the ground, caused by: Fractures in earths crust Volcanic eruptions

3 Stress and Strain Stress causes fractures in rock Three types of stress: Compression Tension Shear Deformation caused by stress is known as strain

4 Compression Compression is stress that decreases the volume of material

5 Tension Tension is stress that pulls a material apart

6 Shear Shear is stress that causes a material to twist

7 Effects of Strain and Stress Stress and strain can cause deformation Low stresses cause elastic strain Elastic strain causes a material to bend and stretch Can return to normal, like a rubber band High stresses cause ductile deformation Material is permanently deformed Can cause breaks or failure

8 Faults When stress causes rock to fail, a fault occurs o Fault – Fracture(s) along which movement occurs Three main types of faults: Reverse Normal Strike-Slip (Transform)

9 Reverse Fault Reverse Faults are fractures that result from horizontal compression Shortens crust horizontally

10 Normal Fault Normal Faults are fractures caused by horizontal tension Lengthens crust horizontally

11 Strike-Slip Fault Strike-Slip Faults are fractures caused by horizontal shear Motion is mainly horizontal

12 Earthquake Waves Vibrations of the ground during earthquakes are called Seismic Waves Three types: Primary Wave (P-Wave) Secondary Wave (S-Wave) Surface Waves

13 P-Waves P-Waves squeeze and pull rocks in the same direction as the wave travels

14 S-Waves S-Waves cause rocks to move at right angles to the direction of the wave

15 Surface Waves Surface Waves move rocks up and down, as well as side-to-side Motion is similar to an ocean wave

16 Focus Earthquakes originate at a point called a Focus Focus is usually below the surface The Epicenter is the point on Earths surface directly above the focus

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