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School of Forensic and Investigative Sciences Assessment Coversheet Module Code Module Title Student’s name Student ID Number Course/ Subject Assignment Title/ Number FZC010 Module Tutor Tina Gornall Physics Rosie Bowers G 2 0 6 2 5 2 Foundation Applied Science 9 How does the analysis of P-waves and S-waves in the inner core, outer-core, mantle and crust allow scientist to determine how the Earth’s interior is structured? ‘I confirm that this piece of work which I have submitted is all my own work and that all references and quotations from both primary and secondary sources have been fully identified and properly acknowledged in footnotes and bibliography.’ Signature: RBowers Extension Agreed date: Date: 23/3/15 Submission Deadline Double line-spaced, on A4 paper In Arial or Times New Roman font in black ink Learning Outcomes To be completed by the student An ability to describe and apply key physics principles necessary for study on university level programmes An ability to present and analyse scientific data and formulate conclusions General comments: 27/2/15 Extension Agreed by: Work submitted should be presented in the following format: 7 Module Tutor Feedback Grade* Rosie Bowers Strengths: Areas for improvement: If there is something you do not understand or some aspect on which you want further information, and you have not yet had the opportunity, you must make an appointment with your tutor to discuss this assessment and the feedback given. You may be asked to use this feedback to reflect upon your personal development (PDP). Upon receipt of the feedback from your module tutor, please complete below your reflections on this assessment for your future action. 1 1st Marker Signature Moderation signature** Date Date Word Count: 755 Rosie Bowers How does the analysis of P-waves and S-waves in the inner core, outer-core, mantle and crust allow scientist to determine how the Earth’s interior is structured? (1) The earth is made up of 4 aligned layers: The inner and outer core, mantle and crust. The crust is the solid surface layer that is made up of tectonic plates. These plates can move and when this occurs pressure is release causing an earthquake. Earthquakes produce P (primary) and S (secondary) seismic waves called as a result. These waves pass through the earth. (2) The P and S wave movement is recorded by a seismometer. A weight with a pen or other writing device is suspended above a sheet of paper. When the earthquakes occurs the seismometer will pick up the tremors and the pen will write to produce a seismograph. In a professional seismometer a lever is used to magnify the signal so that even the smallest earthquake can be recorded. The seismograph will give an indication of the severity of an earthquake. (3) P waves are longitudinal and will reach the seismograph station first and the s waves will be detected second as they are transverse. https://www.sciencenews.org/sites/default/files/images/quakes_followthewave_bottom.png Scientists can also use P and S waves to determine the medium of the earth’s interior layers. (4) As P waves are longitudinal they are the faster of the two seismic waves. They travel by compression and rarefaction of the particles in the earth. As a result they can travel through both the solid and liquid mediums but travel a lot slower through solids than liquids. (2) P waves travel through the mantle at less than 6km h-1 where as they travel at up to 13km h-1 in the core. (3) P waves are also slightly refracted when the medium changes due to this scientist are able to determine that there is a change of medium from the mantle to the inner core. 2 Word Count: 755 Rosie Bowers (3) S waves on the other hand, are transverse. They travel by movement of particles and so are the slower of the two. They do not transmit through liquid medium and so the inner core cannot be penetrated by S waves. S waves will however pass through the mantle this provides scientist with evidence to suggest that the outer core is not a solid structure. As S waves cannot pass through the liquid outer core a ‘shadow zone’ is formed. This is sections of the earth surface in which S waves aren’t detected. This was used to determine the radius of the core of 3470m. Both types of seismic waves, P and S will pass through the mantle and crust layers suggesting that these two structures are very similar in medium. The crust is a solid structure. It is the basis of the earth’s surface and therefore P and S waves will pass through. The mantle is a molten formation that is seen when volcano erupt. It has properties of a liquid and a solid. Due to the solid properties of the mantle S waves can pass through it. The inner core however cannot be penetrated by S waves but P waves can pass through. (4) http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/Images_specific02/p_rays.gif (4) The speed and refraction of the P waves allows scientist to see the changes of state from solid to liquid throughout the earth’s interior but they cannot tell scientists much about the state in which it passing through. It merely tell the scientist that as the depth increase and the P waves travel further into the earth, the velocity of the wave is alters. As shown by the graph below. And so by observation of volcanos and the lava they spew, scientist were able to determine that the structure of the mantle was molten. The graph also show that beyond the outer mantle the S waves cannot go any further. As it is known transverse waves 3 Word Count: 755 Rosie Bowers cannot travel through a liquid and so outer core must be a liquid structure. The graph also suggest that the inner core structure is in fact a solid structure due to the change in velocity from the outer to the inner core. (4) http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/Images_specific02/prem.gif To conclude, using P waves alone cannot tell a scientist much about the earth’s structure as they pass through the crust to inner core. It simply tells them that it is made up of more than one state. The use of S waves in the determination of the structure tell us a little more about the states that the layers consist of due to the impenetrable outer core. 4 Word Count: 755 Rosie Bowers Bibliography. (1) BBC (2014) P and S waves, Available at:http://www.bbc.co.uk/schools/gcsebitesize/science/21c/earth_universe/seismi c_wavesrev1.shtml(Accessed: 23rd March 2015). (2) USGS (Sept 2014) Seismometers, Available at:http://earthquake.usgs.gov/learn/topics/seismology/keeping_track.php (Acces sed: 23rd March 2015). (3) The Royal Society Of Chemistry (1996) Structure of the Earth, Available at:http://www.rsc.org/Education/Teachers/Resources/jesei/waves/home.htm (Ac cessed: 23rd March 2015). (4) CJ Ammon (Jan 2010) Seismic Waves and the Earth's Interior, Available at:http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/ (A ccessed: 23rd March 2015). 5 Word Count: 755