Earthquakes and Seismic Waves

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Earthquakes and Seismic Waves
C5S2

Earthquake Is the shaking that results from the sudden movement of rock along a fault. Is the shaking that results from the movement of rock beneath Earth’s surface

Earthquakes The forces of plate movement causes earthquakes. Plate movement produces stress in Earth’s crust, adding energy to rock and forming faults. Stress increases along a fault until the rock breaks. An earthquake begins. In seconds, the large amount of stored energy is released.

Focus The point beneath Earth’s surface where rock breaks under stress and causes an earthquake

Epicenter The point on Earth’s surface directly above an earthquake’s focus

Types of Seismic Waves

How does the energy of an earthquake travel through Earth?
Seismic waves carry energy from an earthquake away from the Focus, through Earth’s interior, and across the surface.

Seismic Waves There are three types of seismic waves: P waves, S waves, and Surface Waves. An Earthquake sends out two types of waves from its focus: P waves and S waves. When these two reach the surface at the epicenter, surface waves develop.

P waves Also known as Primary Wave
A type of seismic wave that compresses and expands the ground like an accordion. P waves can travel through solids and liquids

S Waves Also known as Secondary Waves or Shear waves
A type of seismic wave that moves the ground surface up and down or side to side S waves can not travel through liquids

Surface Waves A type of seismic wave that forms when P waves and S waves reach Earth’s surface. Surface waves can be shakers (side to side) or rollers (up and down)

Measuring Earthquakes

What are the scales used to measure the strength of an earthquake?
There are three commonly used methods of measuring earthquakes: the Mercalli scale, the Richter scale, and the moment magnitude scale(mms).

Mercalli Scale A Scale that rates earthquakes according to their intensity and how much damage they cause at a particular place. Twelve steps of the Mercalli scale (pg 185). The same earthquake can have different Mercalli ratings because intensity varies in different locations.

Richter Scale A scale that rates an earthquake’s magnitude based on the size of its seismic waves.

Seismograph Seismogram
A device that records ground movements caused by a seismic waves Seismogram The record of an earthquake’s seismic waves produced by a seismograph

Magnitude The measure of an earthquake’s strength based on seismic waves and movement along faults.

The Moment Magnitude Scale
A scale that rates an earthquake by estimating the total energy released.