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- Author or Editor: G. Popescu x
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We present a short review of the most recent results coming from the numerical modeling of seismic hazard and interpretation of the new observations provided by the recently installed seismic stations in Romania. There are still controversial questions related to the asymmetric distribution of the ground motion radiated by the Vrancea intermediate-depth earthquakes and which is the main factor responsible for this particular distribution: seismic source, structural model, site effects or vulnerability. Our main goal is to provide a solution to this key problem, with direct implications upon the seismic hazard assessment. NE-SW elongation of the isoseismals and the maximum values in the Romanian Plain are well explained by the source radiation pattern and the average structural model. The attenuation toward NW is shown to be a frequency-dependent effect, much more important in the high frequency range (≯1 Hz). We conclude that the present seismic hazard of Romania, computed by the deterministic approach, fits well, as a first approximation, the ground motion distribution for the low-frequency band, and the apparent contradiction with the historically-based intensity maps arises mainly from a systematic difference in the vulnerability of the buildings in the intra- and extra-Carpathians regions.
Abstract
In order to determine uranium from raw phosphoric acid solutions, resulted by the sulphuric acid attack of phosphate rocks and the strip solutions of the solvent extraction process for uranium recovery, two classes of analytical methods were established: one for low uranium content in phosphoric acid, and the other for higher uranium concentration in the same medium. The study was based on specific methods, therefore interference probability with other impurities in phosphoric acid medium is low. In the first class, X-ray fluorescence and spectrophotocolorimetric methods were used. X-ray fluorescence was applied on direct raw phosphoric acid solution and raffinate. The last one was associated with solvent extraction [di-(2-ethylhexyl) phosphate + triocylphosphine oxide] on the U(IV)-Arsenazo III complex in strip. The methods of the second class, were used for strip uranium concentrated solutions: X-ray fluorescence isotopic dilution and mass spectrometry, spectrophotocolorimetry and activation analysis associated with gamma-spectrometry. Here spectrophotocolorimetry involves two methods. The first one is based on the U(IV)-Arsenazo III complex and the other on direct U(IV)—phosphoric acid solutions measurements. A good agreement was obtained in each case for all comparative measurements involving various methods.
Abstract
Six groups of Basella Alba L plants grown in different conditions were analysed by using particle induced X-ray emission (PIXE) method to establish a relationship between the elemental map and growth fertiliser conditions. The target samples were bombarded with a 3 MeV protons beam at the tandem accelerator of IFIN-HH Bucharest and the X-rays were detected with a HPGe detector with a 160 eV resolution at the 6.4 keV of K
line of iron. The concentrations obtained have an estimated error of less then 6% for most of the elements analysed.
The seismic hazard assessment in dense-populated areas and the strategic objectives design are based on the study of seismicity of the seismogenic sources (which can have an effect at the site above a specified minimum level that is considered risky) and the attenuation between focus and site. The purpose of this paper is to provide a complete set of information required for a probabilistic assessment of the seismic hazard in the southeast Romania relative to the following seismic sources: Vrancea zone (in the crust and intermediate-depth domains), Predobrogean depression zone, Intramoesian zone and Shabla-Dulovo (Bulgaria) zone. As an example, the obtained input parameters are used to evaluate the seismic hazard distribution due to the crustal earthquakes applying the McGuire's procedure (1976). These preliminary results are in good agreement with the previous research based on deterministic approach (Radulian et al. 2000).
Attenuation specific from Vrancea intermediate-depth focus toward SE is revised at length in order to re-evaluate the seismic hazard at the nuclear power plant (NPP) Cernavoda. To this aim, we took into consideration all the strong motion data available for the region and test a large range of relationship types. Since the instrumental data are limited as magnitude and depth intervals, the extrapolation based on the attenuation laws deduced from these data to great magnitudes is very instable and must be carefully considered. The extrapolation outside the characteristic domain of the available database leads to large deviations, especially at large magnitudes and for the relations which contain the depth as independent parameter.
