dc.contributor.author Irving, Jessica dc.contributor.author Cottaar, Sanne dc.contributor.author Lekic, Vedran dc.date.accessioned 2018-09-20T12:04:54Z dc.date.available 2018-09-20T12:04:54Z dc.date.issued 2018-06 dc.identifier.issn 2375-2548 dc.identifier.uri https://www.repository.cam.ac.uk/handle/1810/280485 dc.description.abstract Turbulent convection of the liquid iron alloy outer core generates Earth's magnetic field and supplies heat to the mantle. The exact composition of the iron alloy is fundamentally linked to the processes powering the convection, and can to be constrained by its seismic properties. Discrepancies between seismic models determined using body waves and normal modes show that these properties are not yet fully agreed upon. Additionally, technical challenges in experimentally measuring the equation-of-state (EoS) parameters of liquid iron alloys at high pressures and temperatures further complicate compositional inferences. We directly infer EoS parameters describing the Earth's outer core from normal mode center frequency observations, and present the resulting Elastic Parameters of the Outer Core (EPOC) seismic model. Unlike alternative seismic models, ours requires only three parameters and guarantees physically realistic behavior with increasing pressure for a well-mixed homogeneous material along an isentrope, consistent with the outer core's condition. We show that EPOC predicts available normal mode frequencies better than the Preliminary Reference Earth Model (PREM) while also being more consistent with body-wave derived models, eliminating a longstanding discrepancy. The velocity at the top of the outer core is lower, and increases with depth more steeply, in EPOC than in PREM, while the density in EPOC is higher than in PREM across the outer core. The steeper profiles and higher density imply the outer core comprises a lighter but more compressible alloy than that inferred for PREM. Furthermore, EPOC's steeper velocity gradient explains differential SmKS body wave travel times better than previous 1D global models, without requiring an anomalously slow $\sim$90-450 km thick layer at the top of the outer core. dc.description.sponsorship J.C.E.I. acknowledges support from the NSF (EAR1644399), and V.L. acknowledges support from the NSF (EAR1345082) and the Packard Foundation. This work started at the 2016 Cooperative Institute for Dynamic Earth Research (CIDER) workshop at the Kavli Institute for Theoretical Physics, University of California, Santa Barbara (supported by the NSF FESD-1135452). dc.publisher American Association for the Advancement of Science dc.rights Attribution-NonCommercial 4.0 International dc.rights.uri https://creativecommons.org/licenses/by-nc/4.0/ dc.title Seismically determined elastic parameters for Earth’s outer core dc.type Article prism.issueIdentifier 6 prism.number eaar2538 prism.publicationName Science Advances prism.volume 4 dc.identifier.doi 10.17863/CAM.27856 dcterms.dateAccepted 2018-05-18 rioxxterms.versionofrecord 10.1126/sciadv.aar2538 rioxxterms.licenseref.uri http://creativecommons.org/licenses/by-nc/4.0/ rioxxterms.licenseref.startdate 2018-05-18 dc.contributor.orcid Cottaar, Sanne [0000-0003-0493-6570] dc.identifier.eissn 2375-2548 rioxxterms.type Journal Article/Review cam.issuedOnline 2018-06-27
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