unseat vs usurp

unseat

verb
  • To remove from some (especially political) position or office; to dethrone. 

  • To cause something to be removed or replaced in its role; to displace, overturn. 

  • To upset the composure of (in various ways); to astound, shock, or unsettle. 

  • To come out or off of a seat. 

  • To remove or dislodge from a seat (especially referring to horse riding). 

usurp

verb
  • To seize power from another, usually by illegitimate means. 

  • To take the place rightfully belonging to someone or something else. 

  • To use and assume the coat of arms of another person. 

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