排序方式： 共有55条查询结果，搜索用时 15 毫秒
11.
Darrel Maddy Tuncer Demir David R. Bridgland Antonie Veldkamp Chris Stemerdink Tim van der Schriek Rob Westaway 《Quaternary Research》2005,63(3):66-346
Investigation of the Pleistocene sequence of the Gediz River, Western Turkey, has revealed a record of Early Pleistocene river terraces. Eleven terraces spanning the interval from 1.67 to 1.245 million years ago (MIS 59–37) are preserved beneath basaltic lava flows. The high number of terraces over this short time period reflects high-frequency sedimentation/incision cycles preserved due to the fortuitous combination of relatively high uplift rates (0.16 mm yr−1) and progressive southwards valley migration. Comparison of this record with ODP967 from the Eastern Mediterranean Basin suggests a link between the production of terraces and obliquity-driven 41,000 year climate cycles in the Early Pleistocene. 相似文献
12.
Turkey confronts loss of life and large economic losses due to natural disasters caused by its morphologic structure, geographical placement, and climate characteristics. The Kuzulu (Koyulhisar) landslide, which caused loss of life and property on 17th March 2005, occurred in an area near the country’s most important active fault, the North Anatolian Fault Zone. To mitigate and prevent landslide damages, prediction of landslide susceptibility areas based on probabilistic methods has a great importance. The purpose of this study was to produce a landslide susceptibility map by the logistic regression and frequency ratio methodologies for a 733-km2 area near the North Anatolian Fault Zone from the southeast of Niksar to Resadiye in Tokat province. Conditioning parameters, such as elevation, slope gradient, slope aspect, distance to streams, roads, and faults, drainage density, and fault density, were used in the analysis. Before susceptibility analysis, the landslides observed in the area were separated into two groups for use in analysis and verification, respectively. The susceptibility maps produced had five different susceptibility classes such as very low, low, moderate, high, and very high. To test the performance of the susceptibility maps, area under curve (AUC) approach was used. For the logistic regression method, the AUC value was 0.708; while for the frequency rate method, this value was 0.744. According to these AUC values, it could be concluded that the two landslide susceptibility maps obtained were successful. 相似文献
13.
Pedrazas Micaela N. Cardenas M. Bayani Hosain Alamgir Demir Cansu Ahmed Kazi Matin Akhter Syed Humayun Wang Lichun Datta Saugata Knappett Peter S. K. 《Hydrogeology Journal》2021,29(4):1601-1610
Fluvio-deltaic aquifers are the primary source of drinking water for the people of Bangladesh. Such aquifers, which comprise the Ganges-Brahmaputra-Meghna Delta, are hydrogeologically heterogeneous. Because of widespread groundwater quality issues in Bangladesh, it is crucial to know the hydrostratigraphic architecture and hydrochemistry, as some aquifer units are contaminated, whereas others are safe. Geophysical methods provide a potentially effective and noninvasive method for extensive characterization of these aquifers. This study applies and investigates the limitations of using electrical resistivity imaging (ERI) for mapping the hydrostratigraphy and salinity of an aquifer-aquitard system adjacent to the Meghna River. Some electrical resistivity (ER) sections showed excellent correlation between resistivity and grain size. These suggest that ERI is a powerful tool for mapping internal aquifer architecture and their boundaries with finer-grained aquitards which clearly appear as low-ER zones. However, in parts of some ER sections, variations in electrical properties were determined by porewater resistivity. In these cases, low ER was indicative of brine and did not indicate the presence of finer-grained materials such as silt or clay. Accordingly, the following hydrostratigraphic zones with different resistivities were detected: (1) aquifers saturated with fresh groundwater, (2) a regional silt/clay aquitard, and (3) a deeper brine-saturated formation. In addition, shallow silt/clay pockets were detected close to the river and below the vadose zone. ERI is thus a promising technique for mapping aquifers versus aquitards; however, the observations are easily confounded by porewater salinity. In such cases, borehole information and groundwater salinity measurements are necessary for ground-truthing.
相似文献14.
Nusret Demir 《Journal of the Indian Society of Remote Sensing》2018,46(8):1265-1272
The purpose of this study is to derive vectoral 3D roof planes from the LIDAR point cloud of the detected buildings. For segmentation of the LIDAR point cloud, the RANSAC algorithm has been used. Because the RANSAC algorithm is sensitive to the used parameters, and results in over- or under-segmentation of the clusters, a refinement method has been proposed. The detection of roof planes has been improved with use of the refinement method. Therefore, similar plane surfaces have been combined, followed by the region-growing algorithm, to split the under-segmented plane surfaces. The digitization of the roof boundaries is performed using the alpha-shapes algorithm, followed by line fitting to generalize the roof edges. The quality assessment has been done using the reference vector dataset with comparison using four different criteria. 相似文献
15.
Gökhan Demir 《Natural Hazards》2018,91(1):133-153
Numerical modelling techniques enable forcing function at the point of contact in a hail impact to be predicted, but many models available in commercial software have not been verified by experiments. A recently developed deterministic model is only able to simulate the impact action of an idealised spherical hailstone. Results recorded from the impact testing of non-spherical simulated hail ice specimens show wide scatters and are different to spherical specimens. A stochastic model has been developed in this study to incorporate the variability of the modelling parameters representing the behaviour of non-spherical ice specimens and to generate time histories of contact force for given impact scenarios. A probabilistic model which was developed previously to provide predictions of the distribution of the size of hailstones in a severe category hailstorm has also been further developed to provide predictions of the maximum contact force values in probabilistic terms. For any given pre-defined forcing function denting into the surface of a steel plate can be estimated by finite element analysis or experimentally on a test machine. The new knowledge base introduced in this paper can be used by manufacturers and designers to re-assess existing products and in making improvements to future installations taking into account cost–benefit considerations. 相似文献
16.
Natural Hazards - Flood emergency management practices cover various aspects of flooding, such as demography, infrastructure, economy, transportation, and agriculture. Emergency managers and local... 相似文献
17.
Rob Westaway Hervé Guillou Ali Seyrek Tuncer Demir David Bridgland Stéphane Scaillet Anthony Beck 《International Journal of Earth Sciences》2009,98(3):601-625
We document the staircase of terraces of the River Tigris in the Diyarbakır area of SE Turkey, in the northern Arabian Platform,
and improve control on the ages of these terrace deposits by dating of overlying basalt flows using the unspiked K–Ar technique.
These fluvial terraces are formed of polymict gravel, including clasts derived from the Anatolian metamorphic terrane farther
north as well as of local basalt. At least 9 Tigris terraces have been recognised so far, the highest of which, ∼200 m above
present river level, marks the local transition from stacked deposition to fluvial incision, the timing of which is bounded
between the mid Late Miocene and the Middle Pliocene. Our K–Ar dating indicates a hiatus in fluvial incision in the late Early
Pleistocene, as basalts dated to 1.22 ± 0.02 and 1.07 ± 0.03 Ma overlie Tigris gravels at very similar levels, ∼60–70 m above
the present river. The lower terraces record the subsequent entrenchment of the modern Tigris valley following an increase
in incision rates in the early Middle Pleistocene, evident from the disposition of younger basalt, dated to 0.43 ± 0.02 Ma,
capping fluvial gravel only ∼21–22 m above the present river level. Numerical modelling can account for the observed uplift
history, as the response to coupling between surface processes and induced flow in the lower crust, with the mobile lower-crust
thin (∼5–7 km thick), consistent with the known presence of a thick layer of mafic underplating at the base of the crust beneath
the Arabian Platform.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
Self-burial processes of finite-length cylinders under oscillatory flows and waves plus currents were examined with the following two different experimental facilities: a large oscillating water-sediment tunnel (LOWST) and a large wave-current tank. More than 130 experiments, with different model cylinders, were conducted within both facilities. The burial mechanisms studied include burial due to local scour and bedform migration. Burial due to fluidization in the tunnel was also explored, but only in a qualitative way. In the case of experiments with LOWST, the equilibrium burial depth was found to be a power function of the shields parameter (thetas). In the wave-current tank, the equilibrium burial depth was also found to be a function of the Shields parameter, albeit with larger scatter. The experimental observations made in both facilities have similar trends but different magnitudes. For equivalent values of the Shields parameter, smaller equilibrium burial depths were observed in the wave flume when compared to the ones in LOWST. After burial induced by local scour takes place, bedform (ripples and sandwaves) formation and evolution play a strong and, in some cases, dominant role on the equilibrium burial depth of the cylinders. Depending on how the vertical dimensions of bedforms compare to the specimen's diameter, cyclical covering and uncovering of the object may take place due to the passage of the migrating sandwaves. In such case, burial depth Bd no longer coincides with the vertical displacement (Vd) of the object as in the case when the burial process is dominated by local scour. 相似文献
19.
20.
Ibrahim Sönmez Ahmet Emre Tekeli Erdem Erdi Fatih Demir Murat Arslan 《Arabian Journal of Geosciences》2014,7(8):3389-3398
Validation of the active fire monitoring (FIR) product from Spinning Enhanced Visible and Infrared Imager sensor of Meteosat Second Generation satellite is performed over Turkey. Ground truth data from the Ministry of Environment and Forestry for the years 2007, 2008, and 2009 is used by taking the active fire months of April–September into consideration. The contingency tables are obtained on a monthly basis and categorical statistics of probability of detection (POD) and false alarm rate (FAR) are derived. The results are introduced for each subclass, namely probable, possible, and combined cases. The highest POD amounts of 8.5, 1.93, and 9.4 % are obtained for the possible, probable, and combined cases, respectively, with the lowest FAR amounts of 70.9, 4.5, and 86.1 % for the same categories. FIR product validation with respect to predefined burnt area thresholds is introduced in the second part of the study in order to investigate burnt area effect in active fire detection. Increasing POD values with respect to burnt area amount is obtained with relatively higher values in probable than possible type. On the other hand, FAR variation is observed to be not correlated with the burnt area amount. 相似文献