(n) an instance of agitation of the earth's crust, Syn. seismic disturbance, Example:the first shock of the earthquake came shortly after noon while workers were at lunch
The Collaborative International Dictionary of English (GCIDE) v.0.53 Collaborative International Dictionary (GCIDE)
{ } a. [ Gr. seismo`s an earthquake, from sei`ein to shake. ] Of or pertaining to an earthquake; caused by an earthquake. [ 1913 Webster ]
Seismic vertical, the point upon the earth's surface vertically over the center of effort or focal point whence the earthquake's impulse proceeds, or the vertical line connecting these two points. [ 1913 Webster ]