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

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