Normal Nor"mal, n. [Cf. F. normale, ligne normale. See Normal, a.] 1. (Geom.) Any perpendicular. 2. (Geom.) A straight line or plane drawn from any point of a curve or surface so as to be perpendicular to the curve or surface at that point. Note: The term normal is also used to denote the distance along the normal line from the curve to the axis of abscissas or to the center of curvature., Fault Fault, n. 1. (Elec.) A defective point in an electric circuit due to a crossing of the parts of the conductor, or to contact with another conductor or the earth, or to a break in the circuit. 2. (Geol. & Mining) A dislocation caused by a slipping of rock masses along a plane of facture; also, the dislocated structure resulting from such slipping. Note: The surface along which the dislocated masses have moved is called the fault plane. When this plane is vertical, the fault is a vertical fault; when its inclination is such that the present relative position of the two masses could have been produced by the sliding down, along the fault plane, of the mass on its upper side, the fault is a normal, or gravity, fault. When the fault plane is so inclined that the mass on its upper side has moved up relatively, the fault is then called a reverse (or reversed), thrust, or overthrust, fault. If no vertical displacement has resulted, the fault is then called a horizontal fault. The linear extent of the dislocation measured on the fault plane and in the direction of movement is the displacement; the vertical displacement is the throw; the horizontal displacement is the heave. The direction of the line of intersection of the fault plane with a horizontal plane is the trend of the fault. A fault is a strike fault when its trend coincides approximately with the strike of associated strata (i.e., the line of intersection of the plane of the strata with a horizontal plane); it is a dip fault when its trend is at right angles to the strike; an oblique fault when its trend is oblique to the strike. Oblique faults and dip faults are sometimes called cross faults. A series of closely associated parallel faults are sometimes called step faults and sometimes distributive faults.