Deformation of partially molten D" layer by small-scale convection and resulting seismic anisotropy and ultralow velocity zone (Okamoto et al., Phys. Earth Planet, Inter., in press)

At the D" layer of the Earth, a cold subducted slab would be heated from below. For a strongly temperature dependent fluid, the resulting thermal instability can be classifed into 3 types as we show below. Among these 3 types, we studied the deformation in a small-scale convection regime. We found that the deformed partial melt can quantitatively explain the observed seismic anisotropy and ultralow velocity zone in the D" layer of the Earth. (movie byTatsuto Okamoto)

(1) Plume dominant regime

Bottom temperature was raised by 1000 K at t=0 (4000K at CMB)

Viscosity contrast is small and hot plumes form.

movie1iavi file)

(2) Transient regime

Bottom temperature was raised by 1500 K at t=0 (4000K at CMB)

A large viscosity contrast causes cellular convection, which eventually merges to form a large-scale instability.

movie2 (avi file: LARGE!)

(3) Small-scale convection regime

Bottom temperature was raised by 2200 K at t=0 (4000K at CMB).

A huge viscosity contrast causes cellular convection to persist, with decreasing wave number with time.

movie3 (avi file: LARGE!)