An earthquake is the vibration of Earth produced by the rapid release of energy

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Focus and Epicenter• Focus is the point within Earth where the

earthquake starts. • Epicenter is the location on the surface directly

above the focus

Faults• Faults are fractures in Earth where movement

has occurred

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Elastic Rebound Hypothesis• Most earthquakes are produced by the rapid

release of elastic energy stored in rock that has been subjected to great forces.

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

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Earthquake Waves

Body Waves• Identified as P waves or S waves

P waves• Are push-pull waves that push (compress) and

pull (expand) in the direction that the waves travel

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S waves• Seismic waves that travel along Earth’s outer

layer• Shake particles at right angles to the direction

that they travel• Travel only through solids• Slower velocity than P waves• A seismogram shows all three types of seismic

waves—surface waves, P waves, and S waves.

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Locating an EarthquakeEarthquake Distance

• The epicenter is located using the difference in the arrival times between P and S wave recordings, which are related to distance.Earthquake Direction

• Travel-time graphs from three or more seismographs can be used to find the exact location of an earthquake epicenter.Earthquake Zones

• About 95 % of the major earthquakes occur in a few narrow zones.

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Seismic wave behaviorP waves arrive first, then S waves, then L and RAverage speeds for all these waves is knownAfter an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.

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• Three seismograph stations are needed to locate the epicenter of an earthquake

• A circle where the radius equals the distance to the epicenter is drawn

• The intersection of the circles locates the epicenter

1.bugnardo.files.wordpress.com/2008/04/08earthquakes_and_earths_interior.ppt -

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The End

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