[ suhb-kruhs-tl ]
/ sʌbˈkrʌs tl /
situated or occurring below the crust of the earth.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for subcrustal
It is perhaps from such a subcrustal layer that the lava of volcanoes is supplied.The Elements of Geology|William Harmon Norton