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371.
Regulatory authorities require estimates of ambient background concentrations (ABCs) of potentially harmful elements (PHEs) in topsoil; such data are currently not available in many countries. High resolution soil geochemical data exist for only part of England and Wales, whilst stream sediment data cover the entire landscape. A novel methodology is presented for estimating soil equivalent ABCs for PHEs from high-resolution (HR) stream sediment geochemical data grouped by common parent materials (PM), using arsenic (As) as an example. Geometric mean (GM) values for local PM groups are used to investigate different approaches for transforming sediment to soil equivalent concentrations. Holdout validation is used to assess: (i) the optimum number of samples for calculating local GM values, and (ii) the optimum scale at which to group data when using linear regression analysis to estimate GM soil ABCs from local sediment geochemical values. Holdout validation showed that the smallest differences were generally observed when five observations were used to calculate the GM and that these should be grouped over the smallest possible area in order to encompass soils over PMs with elevated GM As concentrations. Geometric mean ABCs are estimated and mapped for As in mineral soil across all of England and Wales within delineations of PM polygons. Errors for the estimation of soil equivalent GM As ABCs based on sediment data for an independent validation set were of a similar magnitude to those from holdout validation applied to the original data suggesting the approach is robust. The estimates of soil equivalent ABCs suggest that As exceeds the regulatory threshold used in risk assessments for residential land use (20 mg kg−1) across 16% of the landscape of England and Wales. The applicability of the method for cognate landscapes, and potential refinements is discussed. 相似文献
372.
373.
H. M. Hussein K. M. Abou Elenean I. A. Marzouk A. Peresan I. M. Korrat E. Abu El-Nader G. F. Panza M. N. El-Gabry 《Natural Hazards》2008,47(3):525-546
The aim of the present work is to compile and update a catalogue of the instrumentally recorded earthquakes in Egypt, with
uniform and homogeneous source parameters as required for the analysis of seismicity and seismic hazard assessment. This in
turn requires a detailed analysis and comparison of the properties of different available sources, including the distribution
of events with time, the magnitude completeness, and the scaling relations between different kinds of magnitude reported by
different agencies. The observational data cover the time interval 1900–2004 and an area between 22°–33.5° N and 25°–36° E.
The linear regressions between various magnitude types have been evaluated for different magnitude ranges. Using the best
linear relationship determined for each available pair of magnitudes, as well as those identified between the magnitudes and
the seismic moment, we convert the different magnitude types into moment magnitudes M
W, through a multi-step conversion process. Analysis of the catalogue completeness, based on the M
W thus estimated, allows us to identify two different time intervals with homogeneous properties. The first one (1900–1984)
appears to be complete for M
W ≥ 4.5, while the second one (1985–2004) can be considered complete for magnitudes M
W ≥ 3. 相似文献
374.
375.
376.
Considerable water leakages from reservoirs make it difficult to attain the planned storage capacity. In some cases water leakages give rise to suffusion followed by catastrophes. Until recently methods for locating water leakages were extremely imperfect. Geophysical methods offer good prospects in this direction. For solving these problems, it is effective to use streaming potential measurements, water flow rate observations and thermometry. Laboratory experiments were carried out in connection with the fact that water leakages from reservoirs are characterized by negative anomalies of natural currents; the more filtration discharge, the higher these anomalies are. As a result, the relationship governing the intensity of streaming potential and sand granulometric composition, electrolyte concentrations and other factors were revealed. To determine the velocity of water flowing to leakage sites, a special device, based on the relationship between the temperature of a heated body and its resistance, is applied. This device simultaneously makes it possible to measure the water medium temperature. Observations at reservoir sites were effected by moving along the reservoir non-polarizable potential electrodes and water velocity devices. Recordings were carried out automatically by the recording device of the logging apparatus. Under the conditions of ice cover on water surfaces, measurements were made through separate points by digging holes in the ice cover. Practical field observations were carried out at reservoir sites located in regions where fissured massive rocks as well as loose sediments predominate. In the first case field experiments were carried out in alpine reservoirs, in Armenia. The major water leakages were found to be concentrated on the right bank of the reservoir. In this connection it was not only possible to locate water leakage sites, but also to evaluate their relative intensity. These data were used for planning antifiltration measures. In the second case water leakages from a reservoir located in Uzbekistan in the submontane part of the Pamirs were studied. Streaming potential anomalies and high benthonic flow rates made it possible to discover high filtrations in the base and walls of the dam. Further perfection of these methods should not only permit the determination of water leakage sites and their relative intensity, but also filtration discharges in absolute units. 相似文献
377.
A high resolution Boomer system was used to investigate the bedrock configuration of part of Port Jackson, New South Wales. The continuous reflection profiling technique was successful in delineating a channel incised in bedrock under a thickness of up to 60 m. of unconsolidated sediment covered by up to 20 m. of water. 相似文献
378.
V. A. Williams 《The Photogrammetric Record》1968,6(31):18-23
Topics of immediate practical interest formed the basis of the Address. Particular emphasis was placed upon problems of point transfer, pre-marking of ground control points, aerial triangulation by observation of independent models, and the status of photogrammetric operators. 相似文献
379.
Whole rock RbSr measurements were made on associatedbasic and acid intrusives and extrusives from the northern andsouthern ends of the Lebombo monocline with a view to determineif the acid rocks came from the mantle or from the crust. Inthe south, in Swaziland (now called Ngwame) and Zululand, rhyolitesand granophyres (age 202 14 m.y.) have an initial Si87Sr86ratio of 0.7042 0.0005; in the north, in the Nuanetsi syncline,rhyolites (age 206 13 m.y.) and granites from ring complexes(age 177 7 m.y.) have initial ratios of 0.7081 0.0008 and0.7085 0.0007, respectively. The initial ratios of the basicrocks, basalts and gabbros, vary in both areas and have a rangefrom 0.7042 to 0.7125 which can be explained by crustal contamination.The low initial ratios and isotopic homogeneity of the acidmagmas over long distances (160 km) in Swaziland and Zululandare interpreted as implying that they were derived from themantle. 相似文献
380.