fault vs fault line

fault and fault line both are nouns.

Word	Noun	Adjective	Verb	Adverb
fault	Yes	No	Yes	No
fault line	Yes	No	No	No

fault (noun)	fault line (noun)
a wrong action attributable to bad judgment or ignorance or inattention	(geology) line determined by the intersection of a geological fault and the earth's surface
(sports) a serve that is illegal (e.g., that lands outside the prescribed area)
the quality of being inadequate or falling short of perfection
responsibility for a bad situation or event
(electronics) equipment failure attributable to some defect in a circuit (loose connection or insulation failure or short circuit etc.)
(geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other
an imperfection in an object or machine

fault (verb)	fault line (verb)
put or pin the blame on