foreshock

From fore- + shock.

foreshock (plural foreshocks)

1. (seismology) A small earth tremor which precedes the mainshock in an earthquake sequence.

   Coordinate terms: aftershock, mainshock

2. (figuratively) Any shock or disturbance that precedes an event
   • 1991, D. Roderick Kiewiet, Mathew D. McCubbins, The Logic of Delegation - Page 88:

     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.

• forehocks