Abstract - The thicknesses of fault rock and fault zones and the fault normal separations for breached and intact
relay zones each show a positive correlation with fault displacement. The displacement to thickness
ratio, or average shear strain, varies for the different structures increasing from intact relay zones
(median value - 0.27) to fault rocks (median value - 50). The correlation for fault rocks is widely
interpreted as a growth trend controlled by fault rock rheology, but the progression of displacement to
thickness ratios for the different structures suggests an alternative model. In this alternative model
a fault initiates as an array of irregular fault segments. As displacement increases, relay zones separating
fault segments are breached and fault surface irregularities are sheared off, to form fault zones containing
lenses of fault-bounded rock. With further displacement these lenses are progressively comminuted,
and ultimately converted to zones of thickened fault rock. The final fault rock thickness is
therefore influenced strongly by fault structure inherited from the geometry of the initial fault array. The
large scale range on which fault segmentation and irregularities occur provides the basis for application
of this model over a scale range of at least 7 orders of magnitude.
Journal of Structural Geology, 31, 117-127.