An automated analysis of the southern San Andreas Fault to explore topography’s relationship with tectonics

Abstract

The extraction of topographic metrics from high resolution digital elevation data provide insights into the processes driving landscape evolution, such as climate, tectonics, lithology and biota. From such topographic metrics, erosion rates can be inferred and normalised properties of a landscape can be defined to facilitate comparison of distinct landscapes within a dimensionless framework. This contribution outlines the automatic extraction of hilltop curvatures and reliefs in addition to hillslope lengths and gradients, used to calculate hilltop erosion rates and normalised erosion and relief values along the southern San Andreas Fault. Modern ground motion data is taken from a series of GPS stations across California, which is interpolated into an uplift surface and sampled for each studied hilltop. Topographic metrics can then be considered in their tectonic context to attempt to infer the tectonic influence on the landscape. Hilltop curvature is shown to scale linearly with GPS derived ground motion data, with sharper ridges corresponding to areas undergoing active uplift and hilltop curvatures approaching zero correlating with areas of subsidence. Plots of dimensionless erosion against relief fall below the steady state curve, suggesting a landscape relaxing after the cessation of tectonics. Such a conclusion is unlikely in an actively uplifting landscape and as such it is proposed that the nonlinear flux model does not adequately describe sediment transport in this environment.