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.

River profile response to normal fault growth and linkage: an example from the Hellenic forearc of south-central Crete, Greece

“…Researchers have exploited these evolutionary characteristics of normal fault systems to assess the geomorphic response to step changes in the rate of local rock uplift (Boulton and Whittaker, 2009;Whittaker and Boulton, 2012;Whittaker and Walker, 2015;Kent et al, 2016). Following these previous studies and based on the observation that the Ptolemy and South-Central Crete faults linked in the geologically recent past (< 1 Ma), we infer that along the Tsoutsouros section of the fault uplift rates increased rapidly following linkage.…”

“…This history is consistent with the conceptual model presented in Fig. 2 and supports the findings of numerous other studies that show that river profiles are sensitive recorders of relative uplift histories (Snyder et al, 2000;Whipple, 2001, 2012;Wobus et al, 2006;Whittaker et al, 2008;Boulton and Whittaker, 2009;Pritchard et al, 2009;Whittaker and Boulton, 2012;Perron and Royden, 2013;Royden and Perron, 2013;Goren et al, 2014;Whittaker and Walker, 2015).…”

How concave are river channels?

“…The upper set of knickpoints are attributed to the initiation of faulting and the resulting growth of topography. The lower set of knickpoints are interpreted as the result of subsequent increase (3-5×) in throw rate due to fault linkage (Whittaker and Walker, 2015). The elevations of each group of knickpoints both scale with footwall relief,…”

“…We explore a series of basins draining across faults in the Sperchios Basin, Gulf of Evia, Greece (Figure 11), predominantly cut into 10 clastic sediments (Eliet and Gawthorpe, 1995). Previous work (Whittaker and Walker, 2015) has demonstrated that catchment morphology reflects interaction with these faults. The rivers are typically characterised by convex longitudinal profiles that commonly have two knickpoints.…”

“…Our aim here is not to provide a comprehensive examination of the topography and tectonic evolution of the Sperchios Basin (see Whittaker and Walker, 2015) but to demonstrate the impact of tectonic transience on our ability to quantify m/n.…”