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Density within the Earth?

Density within the Earth?. Mike Warner Earth Science & Engineering Imperial College London. Outline. Earth structure Methods Accuracy Recommendations. Earth Structure. crust vs mantle lithosphere vs asthenosphere ocean vs continent. less accurate. more accurate. chemical composition.

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Density within the Earth?

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  1. Density within the Earth? Mike Warner Earth Science & Engineering Imperial College London

  2. Outline • Earth structure • Methods • Accuracy • Recommendations

  3. Earth Structure • crust vs mantle • lithosphere vs asthenosphere • ocean vs continent

  4. less accurate more accurate chemical composition highly heterogeneous,chemically differentiated thermal boundary layer crust ~ 10 – 50 km (rather) homogeneous& chemically uniform convecting adiabatic interior mantle depth

  5. less accurate more accurate temperature thermal boundary layer lithosphere heterogeneous, strong, complicated ~100 km “asthenosphere” highly viscous, convecting at high Raleigh number well-mixed, homogeneous,simple convecting adiabatic interior depth

  6. Oceans vs Continents Oceans • young • simple • thin crust • mantle density related to cooling Continents • long history • complicated • thick crust • no simple density relationships – more accurate – less accurate

  7. Methods • gravity • seismology • others

  8. Gravity • low resolution • non-uniqueness • density heterogeneity • much improved if boundaries are known from another technique

  9. Seismology • high spatial resolution • good absolute accuracy • determines boundaries • does not measure density directly • elastic properties correlated with density • more money –> better results

  10. Other methods Density varies with • porosity • composition • temperature • pressure Measure or estimate each of these

  11. Accuracy • absolute densities • conversion from seismics • determination of composition • determination of temperature • boundaries • base of sediments • base of crust • base of lithosphere

  12. Profile length • European ~2500 km • Trans-continental ~9000 km

  13. European lithosphere 2500 km

  14. European - continental crust

  15. European - oceanic crust

  16. Errors in density Errors are ~2 sigma(errors not really Gaussian)

  17. Recommendations If at all possible: • source and receiver on oceanic crust • maximum profile length beneath ocean • use maximum profile length • custom seismic experiments

  18. Recommendations Avoid: • Alps • central Europe • thick crust (e.g. Fenoscandia) • Europe to Japan

  19. Recommendations Best profiles: • Western Europe to Eastern US • Atlantic Islands (Canaries, Maderia, Azores) to Portugal, western Spain, NW France, southern Ireland, western England

  20. Errors in density Errors are ~2 sigma(errors not really Gaussian)

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