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beachballs - Focal mechanism Wikipedia the fr ee...

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12/8/13 Focal mechanism - Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Focal_mechanism 1/3 Focal mechanism From Wikipedia, the free encyclopedia The focal mechanism of an earthquake describes the inelastic deformation in the source region that generates the seismic waves. In the case of a fault -related event it refers to the orientation of the fault plane that slipped and the slip vector and is also known as a fault- plane solution . Focal mechanisms are derived from a solution of the moment tensor for the earthquake, which itself is estimated by an analysis of observed seismic waveforms . The focal mechanism can be derived from observing the pattern of "first motions", that is, whether the first arriving P waves break up or down. This method was used before waveforms were recorded and analysed digitally and this method is still used for earthquakes too small for easy moment tensor solution. Focal mechanisms are now mainly derived using semi- automatic analysis of the recorded waveforms. [1] Contents [ hide ] 1 Moment tensor solutions 1.1 Graphical representation ("beachball plot") 2 Beach Ball Calculator 3 See also 4 References 5 External links Moment tensor solutions [ edit ] The moment tensor solution is typically displayed graphically using a so- called beachball diagram. The pattern of energy radiated during an earthquake with a single direction of motion on a single fault plane may be modelled as a double couple , which is
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