a bolt from the blue vs thunderbolt

a bolt from the blue

thunderbolt

noun
  • A flash of lightning accompanied by a crash of thunder. 

  • An event that is terrible, horrific or unexpected. 

  • Vehement threatening or censure; especially, ecclesiastical denunciation; fulmination. 

  • A very powerful shot. 

  • A belemnite, or thunderstone. 

  • A daring or irresistible hero. 

  • A charge in the form of two joined bundles with four rays of lightning emerging from them, resembling the thunderbolt of Jupiter. 

How often have the words a bolt from the blue and thunderbolt occurred in a corpus of books? (source: Google Ngram Viewer )