Editing Geophysics (section)

=== Vibrations ===
{{Main|Seismology}}
[[Image:Pswaves.jpg|thumb|upright=1.3|Illustration of the deformations of a block by body waves and surface waves (see [[seismic wave]]) |alt=Deformed blocks with grids on surface.]]
[[Seismic wave]]s are vibrations that travel through the Earth's interior or along its surface.<ref>{{Cite web |date=2024-01-12 |title=Seismic wave {{!}} Earth's Interior Structure & Movement {{!}} Britannica |url=https://www.britannica.com/science/seismic-wave |access-date=2024-02-18 |website=www.britannica.com |language=en}}</ref> The entire Earth can also oscillate in forms that are called [[normal modes]] or [[seismic wave#Normal modes|free oscillations of the Earth]]. Ground motions from waves or normal modes are measured using [[seismograph]]s. If the waves come from a localized source such as an earthquake or explosion, measurements at more than one location can be used to locate the source. The locations of earthquakes provide information on plate tectonics and mantle convection.<ref name=Shearer>{{cite book|last=Shearer|first=Peter M.|title=Introduction to seismology|year=2009|publisher=Cambridge University Press|location=Cambridge|isbn=9780521708425|edition=2nd}}</ref><ref name=Stein>{{harvnb|Stein|Wysession|2003}}</ref>

Recording of [[seismic wave]]s from controlled sources provides information on the region that the waves travel through. If the density or composition of the rock changes, waves are reflected. Reflections recorded using [[Reflection seismology|Reflection Seismology]] can provide a wealth of information on the structure of the earth up to several kilometers deep and are used to increase our understanding of the geology as well as to explore for oil and gas.<ref name=Telford>{{harvnb|Telford|Geldart|Sheriff|1990}}</ref> Changes in the travel direction, called [[Seismic refraction|refraction]], can be used to infer the [[Earth's interior|deep structure of the Earth]].<ref name=Stein/>

Earthquakes pose a [[Earthquakes#Effects/impacts of earthquakes|risk to humans]]. Understanding their mechanisms, which depend on the type of earthquake (e.g., [[Intraplate earthquake|intraplate]] or [[Deep focus earthquake|deep focus]]), can lead to better estimates of earthquake risk and improvements in [[earthquake engineering]].<ref name=Bozorgnia2004>{{harvnb|Bozorgnia|Bertero|2004}}</ref>