# Earthquakes.  Earthquakes Result from Stress What is an Earthquake? –Definition :  Shaking of a crust by a release of energy – Results :  1. Explosions,

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Earthquakes

 Earthquakes Result from Stress What is an Earthquake? –Definition :  Shaking of a crust by a release of energy – Results :  1. Explosions, fires, broken sewage lines and water mains. Unstable roads, railroads, runways.  2. Tsunamis

Tsunami: Giant ocean wave generated by an earthquake whose epicenter is on the ocean floor. (computer generated photo)

 Causes of Earthquakes Elastic – rebound theory –Definition :  When stress overcomes friction, sudden movement occurs and a snap forward occurs.  This is followed by a rebound or snap back.

 Terminology Focus : –Where earthquakes actually occur below the surface Epicenter : –Point on earth’s surface directly above focus

 Magnitude vs. Intensity Magnitude –Definition:  The amount of energy released by an earthquake. Intensity –Definition:  The amount of damage caused by an earthquake. Intensity: Mercalli Scale Magnitude: Richter Scale - -Scale 1- 12 - Scale 1- 10 1= no damage 30 times more energy as you 12= total destruction go up the scale

 Earthquake Waves Kinds of wave motions –P Waves  Primary (compressional) waves  Can travel through any materials (solid, liquid, gas)  Back and forth waves  Twice as fast as S waves –S Waves  Secondary waves  Side to side waves  Can travel through solids only –L Waves  Surface waves  Slowest moving waves  Cause the most damage

Seismograph: Instrument used to detect and record vibrations from earthquakes.

 Seismogram: Record of an event from seismograph

 Lag Time: Since P waves travel faster than S waves, scientists determine distance to the epicenter by analyzing the difference in arrival times.

 Lag Time:  The longer the lag time between the arrival of the P-waves and the arrival of the S-waves, the farther away the earthquake occurred.

Locating the epicenter Triangulate between 3 or more seismograph stations Where the circles Intersect = an epicenter

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