UC Santa Barbara

Fold scarps, a type of geomorphic scarp formed by folding mechanisms of hinge migration or limb rotation, serve to delineate both fault-bend characteristics and folding histories, which can, in turn, illuminate tectonic processes and seismic hazards associated with thrust systems. Because the subsurface geometry of folds is commonly difficult to determine, existing fold-scarp models, which rely on both the fold type and its causative fault geometries, remain uncertain with respect to the kinematic evolution of a given fold. In this paper, we develop a model to illustrate that, irrespective of specific fold type and subsurface geometries, fold-scarp growth in the mechanism of hinge migration can be successfully reconstructed based on analyses of bed geometry. This model reveals that the underlying bed dips and the ratio of hinge migration distance/hinge width control the fold-scarp shape and slope. During initial growth (ratio<1), the scarp slope increases gradually with migration of the hinge. When the hinge totally exits from its original position (ratio>1), the slope reaches a maximum, which solely depends on underlying bed dips. The scarp height, however, is independent of the hinge width and can be used to quantify folding magnitude. Application of our model to fold scarps in the Mingyaole anticline in the southern foreland of Chinese Tian Shan indicates that the modeled fold-scarp geometry can roughly match with field observations. The Mingyaole shortening rate is estimated to be ≥5.0 mm/a since ~15ka, such that this single fold has accommodated about half of the regional convergence during the Holocene. Key Points Folding through curved hinges creates a distinctive fold-scarp geometry Scarp slope relies on ratio of hinge migration/width, but scarp height is not Shortening rate of the Mingyaole fold is estimated to be ~5.0 mm/a since ~15 ka, such that this single fold has accommodated about half of the regional convergence during the Holocene.