| Noun | 1. | fault line - (geology) line determined by the intersection of a geological fault and the earth's surfacegeology - a science that deals with the history of the earth as recorded in rocks line - a spatial location defined by a real or imaginary unidimensional extent geological fault, fault, fracture, break, shift - (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other; "they built it right over a geological fault" | |