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Earthquakes and Seismic Waves

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by

Ewa Pitcher

on 9 February 2017

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Transcript of Earthquakes and Seismic Waves

Earthquakes
Earth is never still, everyday worldwide, several thousand earthquakes are detected. An earthquake is shaking and trembling that results
from movement of rock beneath Earth's surface.
Earthquakes and Seismic Waves
The forces of plate movement cause earthquake. When plates move they produce stress, form faults. Stress increases along faults
causing earthquake. The earthquake releases energy which travels in the form of seismic waves.
Seismic waves are vibrations that are similar to sound waves, They travel through Earth carrying energy released by an earthquake.
Causes of Earthquakes
Types of Seismic Waves

Focus:
area under beneath Earth's surface where rock was under stress and begins breaks or move.

Epicenter:
the point on the surface directly above the focus.
There are three main categories of seismic waves:
P waves
( primary ): compress and expand ground, travel through solids and liquids
S waves
( secondary) vibrate from side to side or up and down,
cannot move through liquids.
Surface waves
: when P and S waves reach surface, some of them become surface waves. They move more slowly than P and S waves.



How is an Epicenter Located??

Geologists use seismic waves
to locate an earthquakes epicenter.
How Are Earthquakes Measured?

The Modified Mercalli Scale
- rates amount of shaking and trembling. It's based on observation, no instruments are used. It is I ( Roman Numerals 1 ) to XII ( Roman 12)
The Richter Scale
- magnitude scale based on the size of earthquakes waves as recorded by seismographs.
The Moment Magnitude Scale
; rate the total energy an earthquake releases. Earthquakes with magnitude below 5 are small and cause little damage. The most powerful have magnitude above 8, but they are rather rare.
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