Earthquake Behavior


  The earthquake is a dynamic event. When the fault ruptures, energy is released. The energy travels through the earths layers in various wave forms similar to the wavelengths of light coming from the sun that warm our bodies, or wavelengths of sound that reach our ears from some distant sound source. Pictorial descriptions of these waves are shown below. Imagine that a house is planted on the surface of each wave and that it must stay intact during the passing energy wave.



    The original disturbance of the soils and rocks during an earthquake are a mixed bag of movements, fractures, and energy transfer mechanisms. But, the energy waves traveling away from the center of the earthquake (Hypocenter), quickly becomes a set of waves. These waves are the mechanisms that travel outward and ultimately reach structures and do damage. There are four wave types, two body waves and two surface waves. The two body waves are called Primary (P) waves and Secondary (S) waves. The two surface waves are called Love waves and Rayleigh waves. Ironically, much of the damage comes from the Love waves. See the page in this website that provides examples of the four different types of wave behavior. See examples this page.


 in Feet per Second

 Material     P Waves      S Waves

   Basalt          21,000         11,000

   Granite        19,000        10,000

   Wet Sand      4,900           1,975 

    Dry Sand      1,980              780


    Mantle        26,000         11,600

    Crust           21,000          14,800

Measured at Northridge

 At 328 feet Deep                  2,130

  At Bedrock                         6,560



Arrival Times

Travel Times

Amplitude Trace

  Earthquake Recording

  House Response

Modal Analysis

Shake Map

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