1/24/09 Updated 12/23/09 What about Hawaii? Don L. Anderson Normal vs Plume Convection Normal mantle convection is driven by internal radioactive heating, & secular cooling by heat conducted to the surface through a thermal boundary layer The scale of this convection is measured in thousands of km & involves Ts of 100s of degrees Superposed on this is an independent hypothetical smaller scale ( 200 C) form of convection If the inside of the Earth were filled up with uniform slow (red) & fast (blue) cubes, then the globes distributions of earthquakes & seismic stations would return the image on the right Note the poor resolution in the Pacific. Actual data returned the image on the left (From Li et al.). Note the similarity between the real Earth and the fake Earth around Hawaii & south of New Zealand & the redness of poorly sampled regions Note that only red regions are recovered in the Pacific & much of the Indian ocean GLOBAL TOMOGRAPHIC MAP COMPARE RED REGIONS WITH THOSE RECOVERED FROM THE FAKE MANTLE 600 km depth Ritsema et al. There are many large low velocity regions in the mantle. These have the scales of normal mantle convection, not mantle plumes SEMANTICS Ridges & hotspots require extension. Slabs displace warmer material out of TZ. TECTONICS Global extension (red) The test model has a uniform pattern of high and low velocity blocks. Near vertical rays (P,PKP, S, SKS) convert this pattern to vertical slow cylinder Near vertical rays