1. Artefacts & Optical Illusions in Tomography With emphasis on the roles of slabs, backarc basins, volatiles & cratonic roots

2. FACE

3. What is the ambient color? The optical illusion of inversion. Is yellow hot or just not cold?

4. HOT COLORS ARE COLD MANTLE

5. One cause of vertical streaking artefacts (there are many) No plumes Multiple plumes Shallow anisotropy & heterogeneity can bleed into the lower mantle

7. Relative vs. absolute wavespeeds Add the reference model back in

8. Absolute wavespeeds

9. Relative wavespeeds

10. Plumes under California, slab under Yellowstone?

11. The pale yellow areas become slightly positive when a background reference model with slabs at 650 km is added back in and the blue regions above 650 become bluer. In contrast to global reference models, the actual Earth has a global LVZ between 600 and 650 km. Correcting to this new reference turns the red patches above 650 into pale blue or neutral patches & blue regions into flat slab like anomalies. 1000 km

14. Actual anomalies are ~2.5 times larger