Seismic velocity contrasts possibly associated with the lithosphere-asthenosphere boundary under New England
Seismic velocity contrasts possibly associated with the lithosphere-asthenosphere boundary under New England. As shown by the red text, the apparent transition from the lithosphere to the asthenosphere occurs at depths of 89–105 km and is associated with an S-wave velocity decrease of 5–10% over a depth range of 5–11 km. This velocity gradient is too sharp to be explained by a purely thermal boundary between the lithosphere and asthenosphere, and suggests that the asthenosphere is more hydrated or contains a small percent of partial melt. (Image from C.A. Rychert, S. Rondenay, and K.M. Fischer, 2007. P-to-S and S-to-P Imaging of a sharp lithosphereasthenosphere boundary beneath eastern North America, Journal of Geophysical Research, 112, B08314, doi:10.1029/2006JB004619.)