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Today’s Objective: �I will discuss What is an Earthquake?

Do Now:

Go to site & Open the PPT/What is an earthquake

MAKE 3 columns to discuss the features of Primary, secondary, and Surface waves

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the crust is broken up into several large crustal plate. Earthquakes happen when there is movement along the faults lines of the crustal plates

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Earthquakes

– the vibrations of Earth’s crust produced by the rapid release of energy.

- Often caused by slippage along a break in the Earth’s crust.

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Vocabulary

Focus

The point within the Earth where the earthquake starts and energy released

Epicenter

The location on the surface directly above the focus

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San Andreas Fault

California

Faults

- fractures in Earth’s crust where movement has occurred.

(Earthquakes are usually associated with large fractures in the Earth’s crust and mantle.)

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Cause of Earthquakes

When there is movement along a fault stored energy is released. The vibrations of an earthquake as the rocks trying to return to their original state.

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When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.

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Seismology – the study of earthquake waves.

Seismographs –

instruments that

record earthquake

waves.

How are Earthquakes measured?

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Seismogram – a trace produced recording ground motion.

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Two different scales can be used to measure an earthquake:

The Mercalli Scale
The Richter Scale

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The Mercalli Scale

measures how intense an earthquake was based on eyewitness observation
After an earthquake, people report how bad they felt the quake was at their location.
The Mercalli Scale is considered to be subjective because it is based on personal observation, people may disagree about the intensity of the quake.
Especially at a distance from the quake

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The Richter Scale

It measures the strength of the vibrations.
The scale measures the magnitude of quakes from 0 to 9.THE RICHTER SCALE IS A LOGARITHMIC SCALE (X10)
Each magnitude is 10 times stronger than than the previous magnitude.
A “2” on the Richter Scale is 10 times stronger than a “1”.
A “3” is 10 times stronger than a “2”. Which means that a “3” is 100 times stronger than a “1”.

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Three types of Seismic waves

https://www.acs.psu.edu/drussell/demos/waves/wavemotion.html

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Primary Waves �(P–Waves / Compression Waves)

(push-pull waves ) they compress and expand in the direction that the waves travel.
primary waves travel the fastest. �They always arrive first after an earthquake happens.

Travel through solids, liquids, and gases.

Have the greatest velocity of all earthquake waves.

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Secondary Waves �(S–Waves / Transverse Waves)

Particles move 90 ^o(right angles ) to the direction that they travel.
Secondary waves travel slower than p waves. They always arrive second after an earthquake.
Travel only through solids.
Slower velocity than P waves.
They are the shear waves . They sweep the crust from side to side as they pass.�They swept everything right angles as they pass

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Surface Waves �(L- Waves)�

Seismic waves that travel along the Earth’s outer layer (crust)
These are the most destructive earthquake waves
The ground moves up and down and back and forth
They are long period waves. also called Rayleigh and Love waves. And surface waves (because they travel on the surface)
They lift (ELEVATE) the crust as they ripple surface causing the most damage.

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A seismogram shows all three types of seismic waves – first - P waves then - S waves lastly - surface waves.

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Page 11 is used for earthquake questions

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How to find an epicenter

Find the P- wave arrival time and S-wave arrival time.
find the difference in arrival times by subtracting.
Position an index card on the travel time axis
Mark off the difference in arrival time
Move the card over

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Closure:

Why do most earthquakes cause little damage and loss of life?

Because most occur in

areas that are not

populated.

L.A. Earthquake

Earthquake Destruction