Normal fault growth in layered rocks at Split Mountain, Utah: influence of mechanical stratigraphy on dip linkage, fault restriction and fault scaling

Abstract

We analyze displacement profiles measured from a population of normal faults that cut across layered clastic rocks, in order to investigate the controls of mechanical layering on fault growth. Abundant fault tips and displacement minima are found at lithologic contacts, and in some cases are associated with relay structures, suggesting that lithology is responsible for controlling the location of vertical, along-dip segment linkage. Based on the locations and distributions of displacement minima and maxima within the stratigraphic section, as well as the distribution of small faults, we conclude that: (1) most faults initiate within shale beds, and (2) lithologic contacts restrict fault growth at a variety of scales. One consequence of fault restriction is the development of high displacement gradients at fault tips. Because fault tips are only temporarily pinned at bed boundaries, the degree of restriction will fluctuate as faults propagate through the section. In general, maximum displacement (Dmax) across the faults correlates with cross-sectional trace length (L). The Dmax/L ratio decreases as a function of percent shale offset by a fault, and increases as a function of near-tip displacement gradient. An empirically-derived equation relates Dmax/L to rock composition and fault tip displacement gradients, thereby providing a mechanism to predict fault dimensions in the subsurface from limited data.