The Collaborative International Dictionary of English v.0.48:

Earthquake \Earth"quake`\, n.
   A shaking, trembling, or concussion of the earth, due to
   subterranean causes, often accompanied by a rumbling noise.
   The wave of shock sometimes traverses half a hemisphere,
   destroying cities and many thousand lives; -- called also
   earthdin, earthquave, and earthshock.
   [1913 Webster]

   Earthquake alarm, a bell signal constructed to operate on
      the theory that a few seconds before the occurrence of an
      earthquake the magnet temporarily loses its power.
      [1913 Webster]