Overlapping Faults, Intrabasin Highs, and the Growth of Normal Faults

Normal fault systems bounding extensional basins are typically adjoined by a series of subbasins separated by intra-basin highs. The strata within these basins form syndepositional anticlines and synclines whose axes are transverse to the strike of the main bounding fault. One possible explanation for these intrabasin highs is that they result from persistent along-strike deficits in fault displacement. Such deficits are incompatible with scaling relationships observed between fault displacement and length based on large populations of faults. We present data from active normal faults within the Basin and Range province and from inactive normal faults of the Newark basin of eastern North America demonstrating a clear correlation between the along-strike position of overlapping splay faults and the location of intrabasin highs as well as syndepositional transverse folds. Summed displacements for all faults within an intrabasin high are comparable to the displacements on faults bounding flanking subbasins. Older synextensional deposits exhibit localized tilt maxima within subbasins flanking an intrabasin high whereas younger units exhibit uniform tilt patterns across the entire region. Footwall elevation profiles, used as a proxy for fault displacement, define uniform arcuate patterns independent of along-strike position of intrabasin highs. These characteristics of hanging walls and footwalls suggest that intrabasin highs do not represent locations of long-term fault-displacement deficits, but rather are the location of anastomosing fault segments, which upon linking together, rapidly compensate for initial displacement deficits by increased displacement distributed over several splay faults.