A Younger Dryas Ash Bed in western Norway,and its possible correlations with tephra in cores from the Norwegian Sea and the North Atlantic

A bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western Norway. It is formally mamed the Vedde Ash Bed, and its age is approximately 10,600 yr B.P., i.e., mid-Younger Dryas. The bed consits of pure glass having a bimodal basaltic and rhyolitic somposition. The geochemistry of the glass shards suggests an Icelandic source. By means of stratigraphic position and geochemistry, the ash is correlated with ash zones found in cores from the continental shelf, the Norwegian Sea, and the North Atlatic.     

Three-dimensional deformation analysis: Global vector spherical harmonic and local finite element representation

Deformation elements which have global support, such as tidal induced displacements, are represented in terms of vector spherical harmonics. In contrast, local strain and local rotation are represented in terms of irregularly shaped three-dimensional finite elements. These geodetic finite elements reflect the structure of a geodetic network which is arbitrarily shaped. Various continuity classes are discussed. Numerical examples are presented.     

Ground Water Contamination from Creosote Sites

Field data from 44 waste sites contaminated with creosote have been compiled in a database. The data from each site included geological and hydrogeological parameters and the concentrations of creosote compounds in the ground water at various distances from the pollution sources. The creosote compounds that were measured included mononuclear aromatic hydrocarbons and polynuclear aromatic hydrocarbons (PAH) and phenols. Already 50 m down-gradient of the creosote waste sites, 90 percent of the concentrations were from three to 50 times lower than at the source, and most of the median concentrations were below detection limit (0.1 to 0.5 μg/L). The maximum concentrations of benzene, toluene, and xylenes (BTX) and phenols were much lower under aerobic than under anaerobic conditions. Among the phenols, the xylenols (dimethylphenols) appear in higher concentrations under aerobic conditions than phenol and the cresols do. The highest concentrations found were of the same order of magnitude as the calculated solubilities found in the literature, except the chrysene and benz(a)pyrene concentrations, which were one to two orders of magnitude higher than the solubilities.     

Spatial correlation of earthquake ground motion: non-parametric estimation

A non-parametric method, called multidimensional correlation mapping (MCM), is used to describe the local spatial correlation of different components of earthquake ground acceleration. The method estimates spatial correlation without presuming homogeneity or isotropy of the phase-aligned local ground motion fields. For selected events recorded by the SMART1 accelerograph array, we obtain contour plots of equal correlation of ground acceleration, with respect to the center of the array. Displacement time-histories are also computed from the accelerograms and the spatial correlation of the displacements is estimated for comparison with that of the accelerations.     

Dixon resultant’s solution of systems of geodetic polynomial equations

The Dixon resultant is proposed as an alternative to Gröbner basis or multipolynomial resultant approaches for solving systems of polynomial equations inherent in geodesy. Its smallness in size, high density (ratio on the number of nonzero elements to the number of all elements), speed, and robustness (insensitive to combinatorial sequence and monomial order, e.g., Gröbner basis) makes it extremely attractive compared to its competitors. Using 3D-intersection and conformal C ₇ datum transformation problems, we compare its performance to those of the Sturmfels’s resultant and Gröbner basis. For the 3D-intersection problem, Sturmfels’s resultant needed 0.578 s to solve a 6  ×  6 resultant matrix whose density was 0.639, the Dixon resultant on the other hand took 0.266 s to solve a 4  ×  4 resultant matrix whose density was 0.870. For the conformal C ₇ datum transformation problem, the Dixon resultant took 2.25 s to compute a quartic polynomial in scale parameter whereas the computaton of the Gröbner basis fails. Using relative coordinates to compute the quartic polynomial in scale parameter, the Gröbner basis needed 0.484 s, while the Dixon resultant took 0.016 s. This highlights the robustness of the Dixon resultant (i.e., the capability to use both absolute and relative coordinates with any order of variables) as opposed to Gröbner basis, which only worked well with relative coordinates, and was sensitive to the combinatorial sequence and order of variables. Geodetic users uncomfortable with lengthy expressions of Gröbner basis or multipolynomial resultants, and who aspire to optimize on the attractive features of Dixon resultant, may find it useful.     

Lake Winnipeg coastal submergence over the last three centuries

Radiocarbon dating of marsh facies peat and drowned trees along the barrier beaches at the south end of Lake Winnipeg, indicates water levels are presently rising. Lagoonal sediment and associated trees are being buried as the barrier islands move landward in response to rising water levels. Estimates based on radiocarbon dating suggest the water level has been rising 20 cm/century over the last three hundred years. This estimate is consistent with lake level records and models of isostatic uplift which suggest the level of the lake should be rising between 6.7 and 12 cm/century along the south shore. However, additional radiocarbon dates on submerged trees from Observation Point, at the north end of South Basin, and the Spider Islands, near the northern outlet, indicate that at least part of the water-level rise is basin wide. Southward transgression of Lake Winnipeg, throughout the Holocene, is believed to be the result of isostatic tilting of the basin, whereas the recent basin-wide water-level rise is more likely the result of a combination of isostatic tilting and increased precipitation associated with climate change.