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| {{Other uses|Shadowzone (disambiguation)}}
| | [http://koreanyelp.com/index.php?document_srl=1798&mid=SchoolNews clairvoyance] Hi there. Let me telephone psychic ([http://203.250.78.160/zbxe/?document_srl=1792908 203.250.78.160]) begin by introducing the author, her name is Sophia Boon but she never truly favored that title. My spouse and I reside in Kentucky. To climb is some thing she would by no means give up. He is an info officer.<br><br>Feel free to visit my web-site :: free tarot readings ([http://gcjcteam.org/index.php?mid=etc_video&document_srl=696611&sort_index=regdate&order_type=desc http://gcjcteam.org/index.php?mid=etc_video&document_srl=696611&sort_index=regdate&order_type=desc]) |
| [[Image:Earthquake wave shadow zone.svg|thumb|200px|Seismic shadow zone (from [[USGS]])]] | |
| {{Earthquakes}}
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| A seismic '''shadow zone''' is an area of the [[Earth]]'s surface where [[seismograph]]s cannot detect an [[earthquake]] after its [[seismic waves]] have passed through the Earth. When an earthquake occurs, seismic waves radiate out spherically from the earthquake's [[Hypocentre|focus]]. The [[P-Wave|primary seismic waves]] are [[Refraction|refracted]] by the liquid outer core of the Earth and are not detected between 104° and 140° (between approximately {{convert|11570|and|15570|km|mi|abbr=on|disp=or}}) from the [[epicenter]]. The [[S-Wave|secondary seismic waves]] cannot pass through the liquid outer core and are not detected more than 104° (approximately {{convert|11570|km|mi|abbr=on|disp=or}}) from the [[epicenter]].<ref name="USGS Glossary">{{cite web|url=http://earthquake.usgs.gov/learn/glossary/?termID=170&alpha=S |title=Earthquake Glossary - shadow zone |publisher=[[USGS]] |accessdate=May 8, 2011}}</ref><ref name="UoW">{{cite web|url=http://www2.warwick.ac.uk/fac/sci/physics/teach/module_home/px266/diag/shad/ |title=PX266 Geophysics - Extra Material - Seismic shadow zones |publisher=[[University of Warwick]] |accessdate=May 8, 2011}}</ref>
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| The reason for this is that the velocity for P-waves and S-waves is governed by both the different properties in the material which they travel through and the different mathematical relationships they share in each case. The three properties are: [[incompressibility]] (<math>k</math>), [[density]] (<math>p</math>) and [[Stiffness|rigidity]] (<math>u</math>). P-wave velocity is equal to <math>\sqrt{(k+\tfrac{4}{3}u)/p}</math> whereas S-wave velocity is equal to <math>\sqrt{(u/p)}</math> and so S-wave velocity is entirely dependent on the rigidity of the material it travels through. Liquids, however, have zero rigidity, hence always making the S-wave velocity overall zero and as such S-waves lose all velocity when travelling through a liquid. P-waves, however, are only partially dependent on rigidity and as such still maintain some velocity (if greatly reduced) when travelling through a liquid.<ref>{{Cite document|last1=Armstrong |first1=D. |last2=Mugglestone |first2=F. |last3=Richards |first3=R. |last4=Stratton |first4=F. |title=OCR AS and A2 Geology |publisher=[[Pearson Education]] |pages=14 |year=2008|postscript=.}}</ref> Analysis of the seismology of various recorded earthquakes and their shadow zones, led [[geologist]] [[Richard Dixon Oldham|Richard Oldham]] to deduce in 1906 the liquid nature of the Earth's outer core.<ref>{{cite journal |last=Bragg |first=William |year=1936 |title=Tribute to Deceased Fellows of the Royal Society |journal=Science |publisher=American Association for the Advancement of Science |volume=84 |page=544 |issue=2190 |issn=0036-8075 | doi = 10.1126/science.84.2190.539 | bibcode = 1936Sci....84..539B |pmid=17834950}}</ref>
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| ==See also== | |
| *[[Seismic wave]]
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| *[[Ray tracing (physics)]]
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| ==References==
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| {{reflist}}
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| {{DEFAULTSORT:Shadow Zone}}
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| [[Category:Seismology and earthquake terminology]]
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Latest revision as of 08:44, 15 June 2014
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