subsurface vs underneath

subsurface

noun
  • Something that is below the layer that is on the surface. 

  • A surface which is a submanifold of another surface. 

adj
  • below the surface 

underneath

noun
  • The lower surface or part of something. 

  • A background radio sound track played during a specific announcement or program. 

prep
  • Under the control or power of. 

  • Under, below, beneath. 

adv
  • On the underside or lower face. 

  • Below; in a place beneath. 

adj
  • Under, lower. 

How often have the words subsurface and underneath occurred in a corpus of books? (source: Google Ngram Viewer )