This study evaluated the spatial variability of streambed vertical hydraulic conductivity (Kv) in different stream morphologies in the Frenchman Creek Watershed, Western Nebraska, using different variogram models. Streambed Kv values were determined in situ using permeameter tests at 10 sites in Frenchman, Stinking Water and Spring Creeks during the dry season at baseflow conditions. Measurements were taken both in straight and meandering stream channels during a 5 day period at similar flow conditions. Each test site comprised of at least three transects and each transect comprised of at least three Kv measurements. Linear, Gaussian, exponential and spherical variogram models were used with Kriging gridding method for the 10 sites. As a goodness-of-fit statistic for the variogram models, cross-validation results showed differences in the median absolute deviation and the standard deviation of the cross-validation residuals. Results show that using the geometric means of the 10 sites for gridding performs better than using either all the Kv values from the 93 permeameter tests or 10 Kv values from the middle transects and centre permeameters. Incorporating both the spatial variability and the uncertainty involved in the measurement at a reach segment can yield more accurate grid results that can be useful in calibrating Kv at watershed or sub-watershed scales in distributed hydrological models. 相似文献
High‐resolution aeromagnetic data over the Bida Basin, North Central Nigeria has been analysed to investigate the possible continuity of Ifewara fault zone, through the Bida Basin, to Zungeru fault zone. Analytic signal magnitude, horizontal gradient magnitude, and Euler deconvolution methods were applied to the aeromagnetic data to delineate the subsurface structures. The results showed that a prominent NNE–SSW trending fault associated with the Ifewara fault zone extends through the study area. Other faults trending in the ENE–WSW, NE–SW, NW–SE, E–W, and WNW–ESE directions were also mapped. Interpreted models revealed the presence of intrusives and a possible mineralised zone within the study area. We therefore concluded that the inferred fault zones within the basin have affinity with the trend of the Ifewara fault zone, which is an indication of possible extension and linkage with Zungeru fault zone through the Bida Basin. 相似文献
A 6.8-magnitude earthquake that occurred on January 24, 2020, has been effective in Turkey’s eastern regions. The earthquake, with recorded peak ground acceleration (PGA) value of 0.292 g, caused the destruction or heavy damage of buildings, especially in the city center of Elaz?? province. The purpose of this paper was to share the results of detailed investigation in the earthquake-stricken area. Additionally, the causes of damages and failures observed in the buildings were compared to those that had occurred in previous earthquakes in Turkey. In this study, the damages observed in especially RC buildings as well as in masonry and rural buildings were summarized, the lessons learned were evaluated, and the results were interpreted with reference to Turkish earthquake codes. In the study, it was particularly emphasized why the building stock underwent such damage even though the buildings were exposed to earthquake acceleration well below the design acceleration values.
The high-K calc-alkaline granitoids in the northern part of the Mandara Hills are part of the well-exposed post-collisional plutons in northeastern Nigeria. The calc-alkaline rock association consists of quartz monzodiorite, hornblende biotite granite, biotite granites and aplite which intruded the older basement consisting mainly of low-lying migmatitic gneisses and amphibolites during the Neoproterozoic Pan-African Orogeny. Petrological and geochemical studies have revealed the presence of hornblende, iron oxide, and metaluminous to slightly peraluminous characteristics in the granitoids which is typical of I-type granite. The granitoids are also depleted in some high field strength elements (e.g. Nb and Ta) as well as Ti. Plots of Mg# versus SiO2 indicate that the granite was derived from partial melting of crustal sources. Lithospheric delamination at the waning stage of the Pan-African Orogeny possibly triggered upwelling of hot mafic magma from the mantle which underplated the lower crust. This, in turn, caused partial melting and magma generation at the lower to middle-crustal level. However, the peculiar geochemical characteristics of the quartz monzodiorite especially the enrichment in compatible elements such as MgO, Cr, and Ni, as well as LILE element (e.g. K, Ce, Cs, Ba, and Sr), signify that the rock formed from an enriched upper mantle source. The emplacement of high-K granites in the Madara Hill, therefore, marked an important episode of crustal reworking during the Neoproterozoic. However, further isotopic work is needed to confirm this model.
The study area is located on the middle sector of the Malatya-Ovacık Fault Zone (MOFZ) in the eastern Anatolia. Four basaltic flows from bottom to top, which are tholeiitic in character and intercalated with Pliocene sedimentary rocks, were erupted along this fault zone. Chemical compositions of these flows reveal some differences between the first flow and others in terms of high-field strength elements (HFSEs) (e.g. Ti, Zr, Nb). Limited variations in compositions within the first flow and upper flows suggest a limited fractionation range. Trace-element patterns exhibit that all the flows have similar and OIB-like patterns without positive peak at Pb and a trough at Nb—Ta, indicating minimal or no crustal contribution. Rare-earth element (REE) patterns indicate that the first flow has flat patterns with negative Eu anomaly, whereas the upper flows have variable enrichments in LREE and depletions in HREE. La/SmN, Dy/YbN and Zr/Y ratios exhibit that the degree of partial melting decreases from the first flow to upper flows. Higher values of La/YbN ratio for the upper flows and depletions at Y and Yb on the trace-element patterns suggest the presence of garnet as a residual phase, which imply that the depth of partial melting took place solely in the garnet-stability field. OIB-like trace-element patterns and trace-element ratios (e.g. La/Nb, Ce/Y and Zr/Nb) emphasize that the melts forming the Arguvan basalt were originated from the asthenospheric mantle rather than the lithospheric mantle. 相似文献
There are numerous hot springs with temperatures ranging from 30 to 100 °C in Biga peninsula and they occur throughout the peninsula. The result of this study shows that the region is under a tectonic compressional regime. The investigation of the faults and fractures in the region indicates that the region has been affected first by N–S and then E–W compression since the Middle Miocene. Opening fractures and antithetic and synthetic faults due to the compressional movements provide paths for the deep circulation of water. In addition, the tectonic movements, granitic intrusion and volcanic activity have also played important roles as heat sources for the geothermal systems. 相似文献
This report details the result of geophysical exploration for iron ore; which involved vertical magnetic intensity (?Z) and gravity measurements, to delineate the geometry and depth extent of the deposit and acquiring quantitative and qualitative information for pre-drilling purposes in Agbado-Okudu. It is located about 3 km from Jakura along Lokoja-Jakura marble quarry and within low latitude precambrian basement complex district of Kogi State, Nigeria. A total of 517 magnetic measurement points along 16 traverses and 330 gravity reading along 11 profiles on the deposit in northeast–southwest azimuth were undertaken. The magnetic and gravity data enhancement involved linear regression curve fitting and fast Fourier transform, which were used to construct residual magnetic (RM) and gravity (RG) anomalies, analytic signal amplitude, Euler deconvolution at varying spectral indices (SI), power spectrum, and source parameter image (SPI), using the submenu of Geosoft Oasis Montaj software. Interpretation of the RM and RG anomalies revealed a primary causative body which perfectly correlates the positive anomalies and iron ore deposit, in form of a horizontal or gently dipping dyke with strike length of 600 m and average width of 110–130 m, within the gneiss complex in the north and trending south of the area. A secondary causative body associated with the negative anomalies and inferred as a vertical/near vertical thin sheet striking northeast–southwest coincided with the granitic and quartzitic intrusion. The NW–SE and E–W lineament trend conformed Kibarian and Liberian orogeny cycles of generally known structural trends in Nigeria, which shows that the iron ore deposit is structurally controlled. Depths to sources were estimated within range ≤ 2–24 m and 37.5–60 m, regarded as shallow and relatively deep depths, respectively. Ten vertical boreholes ranging in depth between 50 and 100 m are recommended, five of which require a priority attention to ascertain the thickness of the primary causative body. 相似文献
With a clear understanding of the drilling fluid techniques and the cutting-taking mechanism, a new advanced model is set up for analyzing field data and quantitative forecast of cutting-taking mechanism. Therefore, a number of values affecting the drilling rate and the hole cleaning are studied over a wide range of parameters. Drilling data obtained under high-borehole-pressure conditions are analyzed to determine the causes of the reduction in rate of penetration (ROP) as the borehole pressure increases, which in some cases is caused by the buildup of rock debris under the bit. The theoretical achievement and testing conclusions can be very instructional for horizontal well drilling. Much higher annular velocities are required for effective hole cleaning in directional wells than in vertical wells. Highviscosity muds are observed to provide better transport than low-viscosity muds. 相似文献