strip-mine vs unearth

strip-mine

verb
  • To mine by creating a strip mine, usually for coal or tar sands. 

unearth

verb
  • To dig up. 

  • To drive or draw from the earth. 

  • To uncover or find; to bring out from concealment 

How often have the words strip-mine and unearth occurred in a corpus of books? (source: Google Ngram Viewer )