(covers information from several alternate timelines)
A temporal shock wave, also known as a spacetime shock wave or a temporal wavefront, is a powerful buildup of temporal energy which travels through space, changing history as it propagates.
In an alternate timeline, a Krenim weapon ship, constructed by a scientist named Annorax, produced temporal shock waves as byproducts of the temporal incursions it initiated. When the weapon ship eliminated an object from history, a resultant shock wave radiated from the point of the incursion, and altered the timeline to compensate for the absence of the object. This timeline was later negated when, as a result of massive battle damage, a temporal incursion was initiated within the weapon ship itself, erasing it and all of the damage it did to the timeline from history. (VOY: "Year of Hell", "Year of Hell, Part II")