/as then"euh sfear'/ , n. Geol.
the region below the lithosphere, variously estimated as being from fifty to several hundred miles (eighty-five to several hundred kilometers) thick, in which the rock is less rigid than that above and below but rigid enough to transmit transverse seismic waves.
[ 1910-15; asthen ( és ) frail (see ASTHENIA) + -O- + -SPHERE ]