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

https://www.youtube.com/watch?v=yOGoKCK17a4

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.

https://www.youtube.com/watch?v=VSgB1IWr6O4

History of Earthquakes Largest In Magnitude Date Location Magnitude May 22nd, 1960 Chile 9.5 March 28th, 1964 Alaska 9.2 December 26th, 2004 Sumatra (Ocean) 9.1 March 11th, 2011 Japan (Ocean) 9.0 February 27th, 2010 Chile 8.8 Largest In Destruction Date Location Deaths Magnitude Jan 25th, 1556 China 830,000 8 July 27th, 1976 China 655,000 7.5 Aug. 9th, 1138 Syria 230,000 Unknown Dec. 26th, 2004 Sumatra 227,898 9.1 Jan. 12th, 2010 Haiti 222,570 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

https://www. youtube. com/watch https://www.youtube.com/watch?annotation_id=annotation_1885845763&feature=iv&index=2&list=PLNspHwmzscYE2-cUkOfHo92ATHZUqqsPH&src_vid=j0YOXVlPUu4&v=pTtneXyhoPA