earthquake vs unforeseen event

earthquake

verb
  • To undergo an earthquake. 

noun
  • A shaking of the ground, caused by volcanic activity or movement around geologic faults. 

  • Such a quake specifically occurring on the planet Earth, as opposed to other celestial bodies. 

unforeseen event

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