foreshocks

/F AO0 R SH AA0 K S/
noun
  1. 1

    A small earth tremor which precedes the mainshock in an earthquake sequence. Not all mainshocks have foreshocks.

  2. 2

    Any shock or disturbance which precedes an event

Antonyms

Source: https://en.wiktionary.org/wiki/foreshock, https://en.wiktionary.org/wiki/foreshocks