act of God vs calamity

act of God

noun
  • An unforeseen occurrence beyond one's control, such as a natural disaster. 

  • Used other than figuratively or idiomatically: see act, of, God. 

calamity

noun
  • The distress that results from some disaster. 

  • An event resulting in great loss. 

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