Geomorphic constraints on fault throw rates and linkage times: Examples from the Northern Gulf of Evia, Greece

Abstract

We evaluate how the growth and interaction of active normal faults in the Sperchios Basin and Northern Gulf of Evia, Greece, are recorded by the landscape. We demonstrate that patterns in footwall relief along the faults reflect fault segmentation, and we show that in this study area, fault throw is 2 to 3 times the maximum footwall relief. Rivers crossing the faults typically have two knickpoints, which are unrelated to lithology. However, their heights, measured from the active fault trace, vary systematically. The height of the upper set of knickpoints scales linearly with the footwall relief of the faults and is typically >85% of the maximum relief. The height of the lower set of knickpoints also scales with footwall relief, but the heights are consistently lower. The existence of two sets of knickpoints suggests that the rivers have been perturbed by two changes in tectonic rates during faulting. We interpret the upper knickpoints to represent the initiation and growth of fault-generated topography, while the lower set of knickpoints reflects a throw rate increase due to fault linkage. Estimates of throw rate enhancement factor derived from fault interaction theory suggest that the faults increased their rate by a factor of ≥3 when they linked. This constraint, combined with the distribution of knickpoint heights, allows us to estimate the throw rate and linkage time for the faults. The Sperchios Fault has a maximum throw rate of 1.5–2.0 mm/yr, while the Coastal Fault has a maximum throw rate of 0.8–1.2 mm/yr.