Definition of "foreshock"

foreshock

noun
plural foreshocks
1. (geology) A small earth tremor which precedes the mainshock in an earthquake sequence. Not all mainshocks have foreshocks.
2. Any shock or disturbance that precedes an event
  Quotations
  The FY 1981 increases in defense — something of a "foreshock" to the rapid rise in defense spending over the next several years — were prompted by the fall of the Shah in Iran and the Soviet invasion of Afghanistan.
  1991, D. Roderick Kiewiet, Mathew D. McCubbins, The Logic of Delegation - Page 88