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

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 Mw = 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 > 106 years, even in the absence of direct geodetic constraints. © 2008 Elsevier B.V. All rights reserved

The average shape of large waves in the coastal zone

The ability of the NewWave focused wave group (the scaled auto-correlation function) to represent the average shape in time of large waves in a random sea state makes it a useful tool for the design of offshore structures. However, the profile has only been validated against field data for waves on deep and intermediate water depths. A similar validation is advisable when applying NewWave to shallow water problems,where waves are less dispersive and more nonlinear. For this purpose, data recorded by two Channel Coastal Observatory (CCO) wave buoys during two large storms in January 2014 are analysed to assess the ability of NewWave to replicate the average shape of large waves in shallow water. A linear NewWave profile is shown to successfully capture the average shape of the largest waves from the Perranporth and Porthleven wave buoys during these large storm events. The differences between the measurements obtained by a surface-following buoy and a fixed sensor become important when considering the ability of a second-order corrected NewWave profile to capture weakly nonlinear features of the measured data. A general expression for this effect is presented for weakly nonlinear waves on intermediate water depths, leading to Lagrangian second-order sum corrections to the linear NewWave profile. A second-order corrected NewWave profile performs reasonably well in capturing the average features of large waves recorded during the January storms. These findings demonstrate that the NewWave profile is valid in relatively shallow water (kpD values less than 0.5), and so may have potential for use as a design wave in coastal engineering applications

Geomorphic and geological constraints on the active normal faulting of the Gediz (Alaşehir) Graben, Western Turkey.

The Gediz (Alaşehir) Graben is located in the highly tectonically active region of Western Turkey. Extension due to regional geodynamic controls has resulted in a broadly two-phase evolution of the graben; firstly, low-angle normal faulting relating to the exhumation of the Menderes Massif metamorphic core complex took place between 16 - 2.6 Ma. Secondly, high-angle normal faulting initiated ~ 2 Ma forming the Gediz and other E-W trending grabens in the region. Here we quantify the throw rate along the fault array over the last 2.6, 2 and 0.7 Ma using structural and geological constraints, along with analysis of topographic relief as a proxy for footwall uplift. We derive, for the first time, time averaged rates of fault motion from 0.4 mm/yr to 1.3 mm/yr along the strike of the Gediz Graben, with variation in throw-rate associated with the geometry of individual fault strands. Patterns in throw-rate along strike of the graben bounding fault array also suggest that the fault segments have become linked during the last 2.6 - 2 Ma, possibly at 0.8 – 0.7 Ma. Furthermore, these data suggest that an earthquake occurring along the graben bounding fault could have a maximum predicted Mw of 6.3 - 7.6

Normal fault growth and linkage in the Gediz (Alasehir) Graben, Western Turkey, revealed by transient river long-profiles and slope-break knickpoints

The Gediz (Alaşehir) Graben is located in the highly tectonically active and seismogenic region of Western Turkey. The rivers upstream of the normal fault-bounded graben each contain a non-lithologic knickpoint, including those that drain through inferred fault segment boundaries. Knickpoint heights measured vertically from the fault scale with footwall relief and documented fault throw (vertical displacement). Consequently, we deduce these knickpoints were initiated by an increase in slip rate on the basin-bounding fault, driven by linkage of the three main fault segments of the high-angle graben bounding fault array. Fault interaction theory and ratios of channel steepness suggest that the slip rate enhancement factor on linkage was a factor of 3. We combine this information with geomorphic and structural constraints to estimate that linkage took place between 0.6 Ma and 1 Ma. Calculated pre- and post-linkage throw rates are 0.6 and 2 mm/yr respectively. Maximum knickpoint retreat rates upstream of the faults range from 4.5 to 28 mm/yr, faster than for similar catchments upstream of normal faults in the Central Apennines and the Hatay Graben of Turkey, and implying a fluvial landscape response time of 1.6 to 2.7 Myr. We explore the relative controls of drainage area and precipitation on these retreat rates, and conclude that while climate variation and fault throw rate partially explain the variations seen, lithology remains a potentially important but poorly characterised variable

Active normal faults and coupled landscape response: bedrock variability in the southern Gulf of Corinth, central Greece

Fluvial erosion processes control landscape response to climatic and tectonic signals and its propagation into sedimentary basins. Considerable effort has gone into quantifying and modelling the effect of changes in uplift rates on fluvial erosion in bedrock rivers. However, current landscape models, based on stream power, tend to ignore the effects bedrock variability. The lack of available data relating rock strength to bedrock erodibility in fluvial settings has limited our ability to explore this question. Recent attempts at modelling to resolve this issue rely on indirect or theoretical rock strength properties. An alternative approach requires field measurements of rock strength together with geomorphological and tectonic constraints to quantify the effect of rock strength on river evolution. The Gulf of Corinth, central Greece, is one of the fastest extending rifts in the world and tectonic boundary conditions are well constrained. We (1) review published constraints on uplift along the active normal faults on the southern coast of the Gulf, and project uplift away from the faults into three catchments using a viscoelastic dislocation model; (2) test how channel width and slope vary in these rivers upstream of the active faults, and we use this data to estimate the distribution of stream power down-system; (3) systematically measure rock strength, using a Schmidt hammer, to constrain its effect on river response to uplift. All the rivers have knickpoints upstream of the active faults and we show they are responding transiently to active faulting. By assuming that our derived uplift rate equals stream power-driven erosion rate we calculate the erodibility, k, of bedrock. We demonstrate that stream powers in rivers crossing faults in the southern Gulf of Corinth correlate with rock strength and derive a non-linear power relationship between bedrock erodibility k and Schmidt hammer rebound. These findings highlight the need to incorporate bedrock variability into stream power erosion models

Cardiovascular Stress Reactivity and Health: Recent Questions and Future Directions

OBJECTIVE: High cardiovascular reactions to psychological stress are associated with the development of hypertension, systemic atherosclerosis, and cardiovascular disease. However, it has become apparent that low biological stress reactivity also may have serious consequences for health, although less is known about the mechanisms of this. The objective of this narrative review and opinion paper is to summarise and consider where we are now in terms of the usefulness of the reactivity hypothesis and reactivity research, given that both ends of the reactivity spectrum appear to be associated with poor health, and to address some of the key criticisms and future challenges for the research area. METHODS: This review is authored by the members of a panel discussion held at the American Psychosomatic Society meeting 2019 which included questions such as: How do we measure high and low reactivity? Can high reactivity ever indicate better health? Does low or blunted reactivity simply reflect less effort on task challenges? Where does low reactivity originate from, and what is a low reactor? RESULTS: Cardiovascular (and cortisol) stress reactivity are used as a model to: demonstrate an increased understanding of the different individual pathways from stress responses to health/disease and show the challenges of how to understand and best use the reconstruction of a long-standing reactivity hypothesis given recent data. CONCLUSIONS: This discussion elucidates the gaps in knowledge and key research issues that still remain to be addressed in this field, and that systematic reviews and meta-analyses continue to be required

Normal fault evolution and coupled landscape response: Examples from the Southern Apennines, Italy

We present new data addressing the evolution, activity and geomorphic impact of three normal faults in the Southern Apennines: the Vallo di Diano, East Agri and Monti della Maddalena faults. We show that these faults have minimum total throws of ca. 1000-2000 m, and throw rates of ca. 0.7-1 mm year -1 for at least the last ca. 18 ka. We demonstrate that for the Vallo di Diano and East Agri faults, the landscape is effectively recording tectonics, with relief, channel and catchment slopes varying along fault strike in the same manner as normal fault activity does, with little apparent influence of lithology. We therefore use these data to reconstruct the time-integrated history of fault interaction and growth. From the distribution of knickpoints on the footwall channels, we infer two episodes of base level change, which we attribute to fault interaction episodes. We reconstruct the amount of throw accumulated after each of these events, and the segments involved in each, from the fault throw profiles, and use fault interaction theory to estimate the magnitude of the perturbations and past throw rates. We estimate that fault linkage events took place 0.7 ± 0.2 Ma and 1.4 ± 0.3 Ma in the Vallo di Diano fault, and 1 ± 0.1 in the East Agri Fault, and that both faults likely started their activity between 3 and 3.5 Ma. These fault linkage scenarios are consistent with the observed knickpoint heights. This method for reconstructing fault evolution could potentially be applied for any normal faults for which there is information about throw and throw rates, and in which channels are transiently responding to tectonics

Calibrating fluvial erosion laws and quantifying river response to faulting in Sardinia, Italy

It is now widely accepted that rivers modify their erosion rates in response to variable rock uplift rates, resulting in changes in channel slope that propagate upstream through time. Therefore, present-day river morphology may contain a record of tectonic history. The simple stream power incision model can, in principle, be used to quantify past uplift rates over a variety of spatial and temporal scales. Nonetheless, the erosional model's exponents of area and slope (m and n respectively) and ‘bedrock erodibility’ (k) remain poorly constrained. In this paper, we will use a geologically and geomorphically well constrained Plio-Pleistocene volcanic landscape in central Sardinia, Italy, to calibrate the stream power erosion equation and to investigate the slip rate of faults that have been seismically quiescent in the historic past. By analysing digital elevation models, geological maps and Landsat imagery, we have identified the geomorphic expression of several volcanic features (eruption centres and basaltic lava flows) and three normal faults with 6 to 8 km fault traces within the outcrop. Downstream, river longitudinal profiles show a similar transient response to relative base level fall, probably as a result of relief inversion at the edge of the volcanic outcrop. From measurements of incision, local slope and upstream catchment area across eight different rivers, we calculate n ≈ 1, m = 0.50 ± 0.02 and, using a landscape age from literature of 2.7 Ma, bedrock erodibility k = 0.10 ± 0.04 m(1−2m) Myr−1. There are also knickpoints on rivers upstream of two normal faults, and we used numerical inverse modelling of the longitudinal profiles to predict the slip rate of these faults since 2.7 Ma. The results from the inverse model show that the erosional parameter values derived in this study can produce theoretical longitudinal profiles that closely resemble observed river profiles upstream of the faults. The lowest misfit theoretical longitudinal profiles were generated by a model of temporally discontinuous footwall uplift with consistently low throw rates (<0.1 mm yr−1). The predicted footwall uplift history is similar for the two faults, both showing periods of fault slip and no fault movement since 2.7 Ma. Keywords Stream powerNormal faultBasaltSardini

Reconciling bathymetric and stratigraphic expressions of submarine channel geometry

Modern submarine channels form distinctive morphological features on the seafloor and play a critical role in shaping the marine sedimentary record. Recent studies have captured the extremely diverse range of cross-sectional geometries in submarine channels from bathymetric data, which typically display aspect ratios markedly different to the stratigraphic record of ancient submarine channels. Here, we compare and reconcile the relationship between the geomorphic expression of submarine channels as observed on the seafloor and the geometry of their stratigraphic bodies as mapped in seismic-reflection data, using the Niger Delta slope an exemplar. For the same channels, our data allows us to contrast the distribution of widths, depths, and aspect ratios from bathymetric data and at two hierarchical scales in the underlying stratigraphy – the channel element and channel system scale. Channel characteristics are also contextualised with respect to two key variables, the underlying structural template and the relative timescale for which the studied systems have been active. Analysis of the seafloor bankfull geometries highlights substantial variability with widths ranging from ∼300 m to ∼4 km and aspect ratios from ∼10:1–100:1. In contrast, the geometry of stratigraphic channel element bodies remains remarkably consistent across the three channels with widths ∼480–620 m and aspect ratios of ∼9:1. At channel system scale stratigraphic width is comparable to that seen in the bathymetric data, but with aspect ratios of 6–23:1. Our results therefore highlight a marked disparity in the cross-sectional geometries on the present-day seafloor and for their associated channels in the stratigraphic record. We demonstrate that a large part of the disparity between modern and ancient submarine channel geometries may be explained by post-abandonment modification of the seabed channels where there is reduced Holocene activity and we argue this effect likely plays a role in the differences seen in global data sets. These results have significant implications for the use of bankfull process analogues when applied to bathymetric data to estimate submarine channel flow characteristics