National-scale estimation of potentially harmful element ambient background concentrations in topsoil using parent material classified soil:stream–sediment relationships

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.     

Integration and magnitude homogenization of the Egyptian earthquake catalogue

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.     

The Origin of Associated Basic and Acid Rocks in the Lebombo--Nuanetsi Igneous Province, Southern Africa, as implied by Strontium Isotopes

Whole rock Rb–Sr 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 Si⁸⁷–Sr⁸⁶ratio 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.     

Acoustic-gravity wave propagation in an atmosphere with two sound channels

Summary In order to interpret the observed features of pressure records produced by waves from large explosions in the earth's atmosphere, the writers have obtained numerical solutions of the homogeneous equations governing acoustic-gravity wave propagation in a stratified compressible fluid. Theoretical dispersion curves and variations of perturbation kinetic energy with altitude are presented for 11 normal modes. It is shown that the step-like character of the phase velocity curves in the velocity-period plane can be interpreted as being the result of interference between two families of normal modes-«quasi-horizontal modes» representing energy propagation in the lower atmosphere (below the ozonosphere) and «quasi-vertical modes» representing energy propagation in the upper atmosphere (above the ozonosphere). The theoretical prediction that several normal modes contribute to the observed barogram traces is verified by Fourier analysis of a number of wave records.Lamont Geological Observatory Contribution No. 611. — This research was supported by National Science Foundation Grant NSF-G-11997, Office of Naval Research Contract Nonr 266 (70), and National Science Foundation Grant NSF-GP-550. — Part of this research was done at the NASA Institute for Space Studies, New York, N. Y.