THE ROLE OF FAULT SCALE IN CONTROLLING RELAY RAMP SPACING AND OVERLAP IN THE BASIN AND RANGE

Normal faults within the Basin & Range Province of western North America are widely known to be segmented. Fault segment overlap and spacing play a critical role in determining the degree of interaction between two en echelon faults. These parameters are also a fundamental determinant for whether two faults may eventually link to form a longer fault. Previous work on fault overlap (O) and spacing (S) relationships within extensional relay ramps formed by overlapping fault segments shows a self-similarity over 8 orders of magnitude with scatter across 2-3 orders of magnitude. However, prior work has not taken the scale (i.e. length) of the overlapping segments or the total fault size into consideration when examining O/S relationships. This study examines 27 sites within the Basin and Range to investigate the control that fault scale has on the O/S relationship. The sites represent a range of fault scales, which we define by the length of the more basinward overlapping fault, also known as the outboard fault segment. High O/S ratios are associated with relays along shorter (< 15 km long) fault segments, whereas lower O/S ratios are associated with relays along longer faults. The relationships between overlap, spacing and fault scale suggest that lower O/S ratio relays may be more common along longer fault systems because they persist for a longer period of time before becoming well-linked. An impact of this is that the topographic characteristics of low O/S relay ramps survive for longer periods of time in the landscape. These observations are useful because they allow us to predict basin infilling patterns and synrift depocenter locations along extensional basins within the Basin & Range province. Application of these observations to other rifts needs to consider the dimension of the seismogenic thickness, which we interpret as placing an upper bound on the segment spacing, i.e. relay width, on the longest faults.