Extensional fault arrays in strike-slip and transtension

Sedimentary basins developed under conditions of strike-slip or transtension are subject to significant rotational strains, yet faults developed in such regimes are commonly explained using simplified models that ignore rotation. The heaves of extensional faults developed provide a means of quantifying this rotation. For ideal strike-slip (simple shear), the apparent stretch due to fault heaves can be related simply to shear strain. At shear strains (gamma) above 1.0, previously formed extensional faults begin to show inversion as reverse faults, becoming fully inverted at gamma = 2.0. In transtensional basins, the apparent stretch is related, in addition, to the initial orientation of the faults, which may itself be related to the incremental strain. In the Stellarton basin of Nova Scotia, Canada, fault heaves and orientations can be measured from subsurface mine plans. Measurements of these quantities indicate that strain was only mildly transtensional, with a small (< 10degrees) angle of divergence (alpha). The measurement of fault heaves potentially provides detailed information on strain wherever strike-slip or transtensional basins have been explored in detail by seismic or other subsurface methods. (C) 2004 Elsevier Ltd. All rights reserved.