Editing Earthquake (section)

==== Seismic wave arrival ====
As a consequence, the first waves of a distant earthquake arrive at an observatory via the Earth's mantle.

On average, the kilometer distance to the earthquake is the number of seconds between the P- and S wave arrival times, multiplied by 8.<ref>{{cite web |url=http://hypertextbook.com/facts/2001/PamelaSpiegel.shtml |title=Speed of Sound through the Earth |publisher=Hypertextbook.com |access-date=2010-08-23 |archive-date=2010-11-25 |archive-url=https://web.archive.org/web/20101125091130/http://hypertextbook.com/facts/2001/PamelaSpiegel.shtml |url-status=live }}</ref> Slight deviations are caused by inhomogeneities of subsurface structure. By such analysis of seismograms, the Earth's core was located in 1913 by [[Beno Gutenberg]].

S waves and later arriving surface waves do most of the damage compared to P waves. P waves squeeze and expand the material in the same direction they are traveling, whereas S waves shake the ground up and down and back and forth.<ref>{{cite web|url=https://newsela.com/articles/govt-science-earthquakes/id/26756/|title=Newsela {{!}} The science of earthquakes|website=newsela.com|access-date=2017-02-28|archive-date=2017-03-01|archive-url=https://web.archive.org/web/20170301005337/https://newsela.com/articles/govt-science-earthquakes/id/26756/|url-status=live}}</ref>