Editing Seismogram (section)

{{Short description|Graph output by a seismograph}}
{{Cleanup rewrite|poor English and grammar|article or section|date=September 2014}}

[[File:Seismogram at Weston Observatory.JPG|thumb|A seismogram being recorded by a seismograph at [[Weston Observatory (Boston College)|Weston Observatory]] in Massachusetts]]
[[File:Seismogram_on_historical_seismometer_at_Institute_of_Geophysis_of_the_Czech_Academy_of_Science_(14).jpg|thumb|A detail of the seismogram]]
A '''seismogram''' is a graph output by a [[seismograph]]. It is a record of the [[ground motion]] at a measuring station as a function of time. Seismograms typically record motions in three cartesian axes (x, y, and z), with the z axis perpendicular to the Earth's surface and the x- and y- axes parallel to the surface. The energy measured in a seismogram may result from an [[earthquake]] or from some other source, such as an [[explosion]]. Seismograms can record many things, and record many little waves, called [[microseism]]s. These tiny events can be caused by heavy traffic near the seismograph, waves hitting a beach, the wind, and any number of other ordinary things that cause some shaking of the seismograph.

[[Image:Usgs_quake_seis.png|thumb|A set of seismograms for an earthquake from the USGS (click to see large version)]]
Historically, seismograms were recorded on paper attached to rotating drums, a kind of [[chart recorder]]. Some used pens on ordinary paper, while others used light beams to expose photosensitive paper. Today, practically all seismograms are recorded digitally to make analysis by computer easier.<ref name=Bolt>{{citation |last=Bolt |first=Bruce |authorlink=Bruce Bolt |date=August 2005 |title=Earthquakes: 2006 Centennial Update – The 1906 Big One |edition=Fifth |publisher=[[W. H. Freeman and Company]] |isbn=978-0716775485 |page=110}}</ref> Some drum seismometers are still found, especially when used for public display. Seismograms are essential for finding the location and magnitude of earthquakes.