What is an Earthquake?

• Movement of the ground that occurs when rock inside the Earth pass their elastic limit, break suddenly, and experience elastic rebound.

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EARTHQUAKES

• Elastic Limit: the ability of rocks to bend to a certain point.

• Elastic Rebound: Rocks become strained, break, and snap back-rebound back to shape.

EARTHQUAKES

• Folding: Bending of a rock.

• Faulting: Breaking of a rock

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How an Earthquake happens?

1. Rocks become strained or stressed

2. Rocks build up potential energy

3. Energy is released-vibrations move through the earth.

4. Rocks return to normal position with no stress/strain

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The Focus and Epicenter of an Earthquake

• Focus: The point within Earth where faulting begins is the focus, or hypocenter

• Epicenter: The point directly above the focus on the surface is the epicenter

EARTHQUAKES

• Seismic waves-energy waves released during an earthquake.

• Different Types– Primary– Secondary– Surface

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Primary Waves

– a.k.a. = P waves– Fastest wave– First to arrive on a

seismograph– Move back and forth

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Secondary Waves

– a.k.a = S waves– Secondary waves– Second to arrive on

a seismograph– Move side to side

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Surface Waves

– a.k.a = L waves– Slowest waves– Largest waves– Cause most

destruction – Move side to side or

a swaying motion & backward rolling motion

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EARTHQUAKES

• Seismograph-Instrument used to detect seismic waves/vibrations released during an earthquake.

• Seismogram-paper/record of seismic waves.

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EARTHQUAKES• Richter Scale-Magnitude

is based on measurements of amplitudes or heights, of seismic waves as recorded on seismogram.

• Magnitude - the height of the lines traced on a seismogram is a measure of the energy released by the earthquake.

TSUNAMIS

• Seismic sea wave• Powerful seismic

sea wave that begins over an ocean-floor earthquake.

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TSUNAMIS

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