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

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

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 2500 km lithosphere

14. European - continental crust

15. European - oceanic crust

16. Errors in density location length“a priori”“best” Continental 2500 km4.7%2.9% Oceanic 2500 km2.6%1.7% Continental 9000 km2.0%1.7% Oceanic 9000 km1.8%1.5% 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

21. Errors in density location length“a priori”“best” Continental 2500 km4.7%2.9% Oceanic 2500 km2.6%1.7% Continental 9000 km2.0%1.7% Oceanic 9000 km1.8%1.5% Errors are ~2 sigma (errors not really Gaussian)