Quantifying the slip rates, spatial distribution and evolution of active normal faults from geomorphic analysis: Field examples from an oblique-extensional graben, southern Turkey

Abstract

Quantifying the extent to which geomorphic features can be used to extract tectonic signals is a key challenge in the Earth Sciences. Here we analyse the drainage patterns, geomorphic impact, and long profiles of bedrock rivers that drain across and around normal faults in a regionally significant oblique-extensional graben (Hatay Graben) in southern Turkey that has been mapped geologically, but for which there are poor constraints on the activity, slip rates and Plio-Pleistocene evolution of basin-bounding faults. We show that drainage in the Hatay Graben is strongly asymmetric, and by mapping the distribution of wind gaps, we are able to evaluate how the drainage network has evolved through time. By comparing the presence, size, and distribution of long profile convexities, we demonstrate that the northern margin of the graben is tectonically quiescent, whereas the southern margin is bounded by active faults. Our analysis suggests that rivers crossing these latter faults are undergoing a transient response to ongoing tectonic uplift, and this interpretation is supported by classic signals of transience such as gorge formation and hill slope rejuvenation within the convex reach. Additionally, we show that the height of long profile convexities varies systematically along the strike of the southern margin faults, and we argue that this effect is best explained if fault linkage has led to an increase in slip rate on the faults through time from ∼ 0.1 to 0.45 mm/yr. By measuring the average length of the original fault segments, we estimate the slip rate enhancement along the faults, and thus calculate the range of times for which fault acceleration could have occurred, given geological estimates of fault throw. These values are compared with the times and slip rates required to grow the documented long-profile convexities enabling us to quantify both the present-day slip rate on the fault (0.45 ± 0.05 mm/yr) and the timing of fault acceleration (1.4 ± 0.2 Ma). Our results have substantial implications for predicting earthquake hazard in this densely populated area (calculated potential M w = 6.0-6.6), enable us to constrain the tectonic evolution of the graben through time, and more widely, demonstrate that geomorphic analysis can be used as an effective tool for estimating fault slip rates over time periods N 10 6 years, even in the absence of direct geodetic constraints.

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

“…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).…”

“…One promising aspect of this study is that we show that the relative spatial and temporal patterns of uplift can be recorded in river profiles consistent with numerous other studies (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;Whittaker and Walker, 2015). However, other processes, such as waterfall formation, drainage area exchange, karst hydrology and groundwater sapping, the role of sediment in river incision, and chemical weathering, may obscure quantitative predictions about timescales of landscape adjustment and uplift rate history from the modern topography (Prichard et al, 2009;Roberts et al, 2013;.…”

“…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.…”

The kinematics of central-southern Turkey and northwest Syria revisited

“…However, calculations using equation (1) indicate that the DSFZ accommodates left-lateral slip at only ~2-3 mm a -1 in the Misyaf area and across the Ghab Basin in NW Syria Mahmoud et al, 2013), suggesting that a significant component of the relative motion passes southwestward from the KVFZ onto a zone of active faulting along the lower valley of the River Orontes (Asi), downstream of Antakya in the extreme south of Turkey. Active faulting, combining components of left-lateral slip and extension (i.e., left-lateral transtension) has indeed been recognised onshore along the lower Orontes valley (e.g., Boulton and Robertson, 2008;Boulton and Whittaker, 2009;Tüysüz et al, 2013;Figs 2, 3) although this interpretation has been disputed (Karabacak et al, 2010;Karabacak and Altunel, 2013). The published GPS data for this region have been depicted as velocity vector maps many times (e.g., Reilinger et al, 2006, Fig.…”

Long-term geomorphological evolution of the axial zone of the Campania-Lucania Apennine, southern Italy: a review

“…In fact, the fault-slip rates (referred to the vertical component of motion, cf. Boulton & Whittaker 2009) from the upper Agri Valley and Pergola-Melandro basin vary from 0.3 to 0.5 mm/yr in the time interval included between 1.8 -1.2 Ma, and from 0.5 to 0.8 mm/yr in the 1.2-0.7 Ma time span (Schiattarella et al 2003;Boenzi et al 2004). The 0.3 -0.5 mm/yr slip rate value has also been obtained for the Vallo di Diano basin fault system, but in relation to the activity started from the Early-Middle Pleistocene boundary (Giano et al 2014a, b).…”