subsurface
adj.describing something that is hidden or located below the surface of the ground or water.
adj.situated or occurring beneath the surface of the earth or a liquid. Often used in geological or mathematical contexts to describe structures or layers that are not visible from above.
“The subsurface layers of the soil are very dry.”
“Geologists use seismic waves to map the subsurface structure of the earth to find oil and gas reserves.”
“In the study of fluid dynamics, the subsurface flow of water through porous rock is critical for understanding how contaminants might spread across an aquifer.”
“Geologists aren’t certain why Earth has tectonic plates – the current best theory is that the decay of radioactive elements in the interior of the planet produces heat that melts subsurface rock.”
“Especially in densely populated coastal regions, human activities cause the land to subside more strongly - often due to excessive extraction of water and resources that previously stabilized the subsurface.”