The purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what
general conditions govern their geometrical evolution. We pay particular attention to seismological and surface
data from regions of present day active normal faulting, as the instantaneous three-dimensional geometry at the
time of fault movement is better known in active regions than in areas where the faults are now static.
Most normal faults are concave upward, or listric. This shape can be produced by geometric constraints, either
because the faults reactivate curved thrusts, or because they must be curved to accommodate rotations. Another
effect which will produce curved faults is the variation of rheology with depth: brittle failure at shallow depths
produces less fault rotation than does distributed creep in the lower part of the crust. An important geometric
feature of normal faulting is the uplift of the footwall. The amount of such uplift is related not only to the elastic
properties of the lithosphere, but also to the throw and dip of the fault. A striking feature of active normal faults
is that they occur in groups in which all the faults dip in the same direction. This behaviour arises because the faults
cannot intersect: if they do, one must cease to be active. The rotation which such fault systems produce reduces
the dip of the faults until a new steeply dipping fault is formed. Once a new fault cuts pre-existing faults the earlier
faults become locked, and a new set of faults must propagate rapidly across the whole region involved. Many of
these geometric constraints also apply to thrust faulting.