A Hybrid Collocation Method For Calculating Complete Theoretical Seismograms In Vertically Varying Media

A numerical method is presented for calculating complete theoretical seismograms, under the assumption that the earth models have velocity, density and attenuation profiles which are arbitrary piece-wise continuous functions of depth only. Solutions for the stress-displacement vectors in the medium are expanded in terms of orthogonal cylindrical functions. Our method for solving the resulting two-point boundary value problems differs from that of other investigators in three ways. First, collocation is used in traditionally troublesome situations, e.g. for highly evanescent waves, at turning points, and in regions having large gradient in material properties. Second, in some situations (high frequencies and small gradients) P and S -waves decouple and we use a different solution method for each wave type, instead of trying to force a single method to find all solutions. For example, above the P - and S -waves turning points an approximate fundamental matrix may be used for each wave type. At the P -wave turning point, the fundamental matrix may be used for the S -wave components but collocation is used for the P -wave. Between the P - and S -wave turning points collocation is used for the evanescent P -wave and the fundamental matrix is used for the S -wave. At the S -wave turning point and below, collocation is used for both. Third, the computational algorithm chooses the appropriate solution method and depth domain upon which it is employed based upon a specified error tolerance and the known inaccuracies of the various approximations employed. Once solutions of the boundary value problems are obtained, a Fourier—Bessel transform is then applied to get back into the space-time domain.     

Biological marker characteristics of oils and asphalts from carbonate source rocks in a rapidly subsiding graben,Dead Sea,Israel

A detailed GC/MS study of biological marker compounds in the saturated and aromatic hydrocarbon fractions of oils and asphalts from the Dead Sea area, Israel, provided decisive information to the solution of a long-lasting controversy by showing that the asphalts are products of early generation in an immature stage from the same type of carbonate source rock which generated more mature oils. The asphalts are not biodegraded residues of the oils.Oils from six different wells, and asphalts from wells, outcrops, and a floating block from the Dead Sea all have very similar sterane and triterpane patterns. They all lack rearranged steranes (diasteranes) indicating a carbonate source matrix and compare reasonably well with a sample of Upper Cretaceous bituminous chalk from Nebi Musa. The main difference between the oils and the asphalts is a significantly higher triaromatic to mono- plus triaromatic steroid hydrocarbon ratio in the former. This is explained as a result of rapid subsidence and heating of their source rock close to the deep parts of the Dead Sea graben. The oils thus were generated in the more deeply buried source rock blocks under the graben fill, whereas the asphalts either originate from an immature source rock section closer to the graben rims or represent an earlier phase of generation and expulsion.This study also provides general information on the evolution of biological markers in carbonate source rocks. Low-activation-energy processes, like isomerisation of steranes, appear to occur much faster at low temperatures than in shales. The high sulfur content and less cross-linking of the biogenic organic matter into a complex kerogen structure are suggested to be responsible for this. Care should be taken when using only sterane isomerisation to assess the maturity of hydrocarbons from carbonate rocks and of carbonate-derived oils.     

Role and timing of complementary objectives of a regional policy,the case of Northern Israel

The lessons of a regional development policy for Northern Israel are evaluated. The policy has been led by two complementary objectives: the creation of a demographic balance in favour of Jews and the geographical development of a continuous network of Jewish settlements. Each objective had its appropriate spatial timing in the regional process. The first took advantage of geopolitical needs, ideological values and social conditions of the evolving nation during its pre-state and its early years. Attempts to reach the other objective through urban development programmes had failed until recently due to the strong polarization effects of Metropolitan Haifa. Starting in the mid 1970s, spontaneous metropolitan spread effects have created favourable conditions of growth. They have been reflected by both urban growth and massive rural development throughout the spillover effect area of the metropolis.     

Assessing a farmer's decision concerning the application timing of nitrogen fertilizer

This paper is concerned with a farmer's decision on the timing of nitrogen fertilizer application. Analytical models are developed to determine the necessary conditions for the optimal timing of the application of nitrogen fertilizer. The models, coupled with an estimated cotton yield function, are used to assess a farmer's decision on the optimal application timing of nitrogen fertilizer in cotton production. The empirical results explain various observed application timings of nitrogen fertilizer being used in cotton production in Mississippi, USA, and provide an estimate of the cost to a farmer when he or she must comply with a restriction on the timing of the application of nitrogen fertilizer.The views expressed are those of the authors, and do not necessarily represent the policies of the US Department of Agriculture or the views of other US Department of Agriculture staff members     

Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic (C,O, <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr) data from Kangankunde,Malawi

Carbonatites host some of the largest and highest grade rare earth element (REE) deposits but the composition and source of their REE-mineralising fluids remains enigmatic. Using C, O and ⁸⁷Sr/⁸⁶Sr isotope data together with major and trace element compositions for the REE-rich Kangankunde carbonatite (Malawi), we show that the commonly observed, dark brown, Fe-rich carbonatite that hosts REE minerals in many carbonatites is decoupled from the REE mineral assemblage. REE-rich ferroan dolomite carbonatites, containing 8–15 wt% REE₂O₃, comprise assemblages of monazite-(Ce), strontianite and baryte forming hexagonal pseudomorphs after probable burbankite. The ⁸⁷Sr/⁸⁶Sr values (0.70302–0.70307) affirm a carbonatitic origin for these pseudomorph-forming fluids. Carbon and oxygen isotope ratios of strontianite, representing the REE mineral assemblage, indicate equilibrium between these assemblages and a carbonatite-derived, deuteric fluid between 250 and 400 °C (δ¹⁸O + 3 to + 5‰_VSMOW and δ¹³C ? 3.5 to ? 3.2‰_VPDB). In contrast, dolomite in the same samples has similar δ¹³C values but much higher δ¹⁸O, corresponding to increasing degrees of exchange with low-temperature fluids (< 125 °C), causing exsolution of Fe oxides resulting in the dark colour of these rocks. REE-rich quartz rocks, which occur outside of the intrusion, have similar δ¹⁸O and ⁸⁷Sr/⁸⁶Sr to those of the main complex, indicating both are carbonatite-derived and, locally, REE mineralisation can extend up to 1.5 km away from the intrusion. Early, REE-poor apatite-bearing dolomite carbonatite (beforsite: δ¹⁸O + 7.7 to + 10.3‰ and δ¹³C ?5.2 to ?6.0‰; ⁸⁷Sr/⁸⁶Sr 0.70296–0.70298) is not directly linked with the REE mineralisation.     

Indication for circular organization of column sprite elements associated with Eastern Mediterranean winter thunderstorms

We report synchronized optical observations of sprites in Israel during the winters of 2006/7–2007/8. Based on several events, we suggest that the elements of columniform sprites are organized in spaced intervals on the circumference of a circle centered directly above, or a little offset, to the vertical direction from the parent lightning. In 2D images most of the cases show columns to be arranged in highly eccentric elliptical forms or in straight rows. The analysis of the optical images provided the geometrical dimensions of the columns and their spatial organization. We used an electrostatic model of the QE field with reasonable assumptions on the location and magnitude of the cloud charge center, constrained by ELF evaluation of the Charge Moment Change in the parent flash, to show that the observed diameter of the columnar arrangement closely matches the conventional breakdown field line contour at the same altitude.