Earthquakes Seismic Waves An Earthquake occurs when energy

Earthquakes & Seismic Waves

An Earthquake occurs when energy is released through rapid movement along a fault.

Current Earthquake Data http: //ds. iris. edu/seismon/

Focus That is the point along the fault line where the rock under stress breaks.

Epicenter Is the point on the earth’s surface directly above the Focus.

Focal Depth This is the distance between the Focus and the Epicenter.

Seismic Waves Energy from an Earthquake is carried away from the focus as Seismic Waves. There are many different types of waves. We will concentrate on the two most prominent.

Primary Waves P Waves The fastest seismic wave. Arrives at recording stations first (Primary).

Primary Waves P waves are compressional waves. The energy travels in the same direction as the wave travels.

Primary Waves P waves can travel through solids, liquids or gases.

Secondary Waves S Waves Arrives at recording stations second (secondary).

Secondary Waves S waves are transverse waves. Another term is shear waves. The energy is perpendicular to the direction of wave travel.

Secondary Waves S Waves can only travel through solids.

Surface Waves like L waves and R waves travel slightly slower then S waves but do tremendous damage.

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Seismograph Instruments that detect and measure seismic waves are called Seismographs. They originally were a weight and pen suspended over a moving drum.

Seismograph The tracing on the drum is called a seismogram. The different types of waves make different tracings on the seismogram.

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History of Earthquakes Largest In Magnitude Date May 22 nd, 1960 March 28 th, 1964 December 26 th, 2004 March 11 th, 2011 February 27 th, 2010 Largest In Destruction Date Jan 25 th, 1556 July 27 th, 1976 Aug. 9 th, 1138 Dec. 26 th, 2004 Jan. 12 th, 2010 Location Chile Alaska Sumatra (Ocean) Japan (Ocean) Chile Location China Syria Sumatra Haiti Deaths 830, 000 655, 000 230, 000 227, 898 222, 570 Magnitude 9. 5 9. 2 9. 1 9. 0 8. 8 Magnitude 8 7. 5 Unknown 9. 1 7. 0

Locating an Earthquake Epicenter… To find where the an Earthquake originates you need wave data from 3 recording stations. Circles are drawn around these stations. Where the 3 circles connect is where the earthquake originated.

Underwater E-quake Fault movement along the ocean floor moves the water up and down which can create a massive wave called a “Tsunami”.

Tsunami

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