Shear experiments on olivine-basalt aggregates provide compelling evidence
that the dynamic distribution of melt is controlled by the magnitude and or
ientation of the differential stress. Our results suggest that deformed, pa
rtially molten upper mantle rocks will have highly anisotropic physical pro
perties including seismic wave velocities and melt permeability. In additio
n, our results provide a basis for interpreting geophysical observations, s
uch as shear-wave splitting and for modeling melt migration processes benea
th mid-ocean ridges, specifically focused flow of melt toward the ridge axi
s.