The reduction in length of a line as a result of strain, e.g. by thickening, folding, thrusting, or the loss of material by solution. Simple shortening may be calculated using the same equation as for extension (e): e = (L_F – L_O)/L_O, where L_F is the final length and L_O the original length; if e has a negative value when calculated from this equation, the line has been shortened.