asˈthenəˌsfi(ə)r, əsˈth- noun
( -s )
Etymology: asthen- + -sphere
: a hypothetical earth-circling shell or zone which lies from 30 to 75 miles below the earth's surface and within which the material not necessarily molten is believed to yield more readily to persistent stresses than the rigid crust above or the solid nucleus below — called also tectosphere, zone of mobility, zone of weakness ; compare sima , zone of flow