Integration of stress testing with graph theory to assess the resilience of urban road networks under seismic hazards

Transportation networks daily provide accessibility and crucial services to societies. However, they must also maintain an acceptable level of service to critical infrastructures in the case of disruptions, especially during natural disasters. We have developed a method for assessing the resilience of transportation network topology when exposed to environmental hazards. This approach integrates graph theory with stress testing methodology and involves five basic steps: (1) establishment of a scenario set that covers a range of seismic damage potential in the network, (2) assessment of resilience using various graph-based metrics, (3) topology-based simulations, (4) evaluation of changes in graph-based metrics, and (5) examination of resilience in terms of spatial distribution of critical nodes and the entire network topology. Our case study was from the city of Kathmandu in Nepal, where the earthquake on April 25, 2015, followed by a major aftershock on May 12, 2015, led to numerous casualties and caused significant damage. Therefore, it is a good example for demonstrating and validating the developed methodology. The results presented here indicate that the proposed approach is quite efficient and accurate in assisting stakeholders when evaluating the resilience of transportation networks based on their topology.     

Environmental isotopic evaluation of the springs located in Kazan Trona basin in Central Turkey

Kazan Trona ore field, the second discovered deposit in Central Turkey, is planned to be extracted by solution mining technology. Understanding the hydrogeology of the springs in such an area is vital since they can be affected during mining operations. The aim of this study is to provide an isotopic approach by utilizing environmental isotope techniques to the springs in the study area, thereby, to enhance the understanding of their occurrence by complementing the previous geochemical studies. Here, the isotopic signatures and the recharge elevations of the springs are demonstrated together with their field parameters. The relationship between ??D and ??¹⁸O suggest strong evaporation in some of the samples after recharge. For those springs, the unmodified signatures were determined and the recharge elevations were calculated to be between 1100 and 1248 m. These elevations correspond to Incirlik and Asmalidere Members and upper Neogene units. The relationship between Tritium and Electrical Conductivity suggested that SP-6, SP-3 and SP-4 have shallow circulation when compared to SP-7 having both the lowest tritium and highest EC value. This finding is in accordance with the geochemical data, which suggests SP-7 emerges from the deeper, older groundwater present above the trona deposit.     

GIS-based stochastic modeling of physical accessibility using GPS-based floating car data and Monte Carlo simulation

The term physical accessibility has long been used by geographers, economists, and urban planners and reflects the relative ease of access to/from several urban/rural services by considering the traveling costs. Numerous accessibility measures, ranging from simple to sophisticated, can be observed in the geographical information systems (GIS)-based accessibility modeling literature. However, these measures are generally calculated from a constant catchment boundary (a most likely or average catchment boundary) based on constant deterministic transportation costs. This is one of the fundamental shortcomings of the current GIS-based accessibility modeling and creates uncertainty about the accuracy and reliability of the accessibility measures, especially when highly variable speeds in road segments are considered. The development of a new stochastic approach by using global positioning system (GPS)-based floating car data and Monte Carlo simulation (MCS) technique could enable handling the variations in transportation costs in a probabilistic manner and help to consider all possible catchment boundaries, instead of one average catchment boundary, in accessibility modeling process. Therefore, this article proposes a stochastic methodology for GIS-based accessibility modeling by using GPS-based floating car data and MCS technique. The proposed methodology is illustrated with a case study on medical emergency service accessibility in Eskisehir, Turkey. Moreover, deterministic and stochastic accessibility models are compared to demonstrate the differences between the models. The proposed model could provide better decision support for the decision-makers who are supposed to deal with accessibility, location/allocation, and service/catchment area related issues.     

Hydrogeological and hydrogeochemical characterization of a karstic mountain region

Karstic limestone formations in the Mediterranean basin are potential water resources that can meet a significant portion of groundwater demand. Therefore, it is necessary to thoroughly study the hydrogeology and hydrogeochemistry of karstic mountain regions. This paper presents a detailed hydrogeological and hydrogeochemical characterization of the Nif Mountain karstic aquifer system in western Turkey, an important recharge source for the densely populated surrounding area. Based on the geological and hydrogeological studies, four major aquifers were identified in the study area including the allochthonous limestone in Bornova flysch, conglomerate-sandstone and clayey-limestone in Neogene series, and the Quaternary alluvium. Physicochemical characteristics of groundwater were measured in situ, and samples were collected at 59 locations comprised of springs and wells. Samples were analyzed for major ions, isotopic composition, arsenic, boron and heavy metals among other trace elements. It was found that the hydrogeological structure is complex with many springs having a wide range of discharge rates. High-discharge springs originate from allochthonous limestone units, whereas low-discharge springs are formed at the contacts with claystone and limestone units. Using stable isotope analysis data, a δ¹⁸O-deuterium relationship was obtained that lies between the Mediterranean meteoric and mean global lines. Tritium analyses showed that low-discharge springs originating from contact zones had longer circulation times compared to the high-discharge karstic springs. Furthermore, hydrogeochemical data revealed that groundwater quality significantly deteriorated as water moved from the mountain to the plains. Heavy metal, arsenic and boron concentrations were generally within drinking-water quality standards with a few exceptions occurring in residential and industrial areas located at the foothills of the mountain. Elevated arsenic concentrations were related to local geologic formations, which are likely to contain oxidized sulfite minerals in claystones. It is concluded that Nif Mountain overall has a significant potential to provide high-quality water with a safe yield of at least 50 million m³/year, which corresponds to about 28% of the mean annual inflow to the Tahtali reservoir, a major water resource for the city of Izmir. An erratum to this article can be found at     

Improvement of statistical landslide susceptibility mapping by using spatial and global regression methods in the case of More and Romsdal (Norway)

Statistical models are one of the most preferred methods among many landslide susceptibility assessment methods. As landslide occurrences and influencing factors have spatial variations, global models like neural network or logistic regression (LR) ignore spatial dependence or autocorrelation characteristics of data between the observations in susceptibility assessment. However, to assess the probability of landslide within a specified period of time and within a given area, it is important to understand the spatial correlation between landslide occurrences and influencing factors. By including these relations, the predictive ability of the developed model increases. In this respect, spatial regression (SR) and geographically weighted regression (GWR) techniques, which consider spatial variability in the parameters, are proposed in this study for landslide hazard assessment to provide better realistic representations of landslide susceptibility. The proposed model was implemented to a case study area from More and Romsdal region of Norway. Topographic (morphometric) parameters (slope angle, slope aspect, curvature, plan, and profile curvatures), geological parameters (geological formations, tectonic uplift, and lineaments), land cover parameter (vegetation coverage), and triggering factor (precipitation) were considered as landslide influencing factors. These influencing factors together with past rock avalanche inventory in the study region were considered to obtain landslide susceptibility maps by using SR and LR models. The comparisons of susceptibility maps obtained from SR and LR show that SR models have higher predictive performance. In addition, the performances of SR and LR models at the local scale were investigated by finding the differences between GWR and SR and GWR and LR maps. These maps which can be named as comparison maps help to understand how the models estimate the coefficients at local scale. In this way, the regions where SR and LR models over or under estimate the landslide hazard potential were identified.