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31.
Any calculation of seismic wave propagation comprising the seismic source, the travel path, and the receiver site in a single finite-difference (FD) model requires a considerable amount of computer time and memory. Moreover, the methods currently available for including point sources in the 2D FD calculations are far-field approximations only. Therefore we have developed a new hybrid method for treating the seismic wave fields at localized 2D near-surface structures embedded in a 1D background medium, and excited by a point source. The source radiation and propagation in the background model is solved by the discrete-wave number (DW) method, while the propagation in the local 2D structure is calculated by the FD method. The coupling between the two sets of calculations is performed on a rectangular excitation box surrounding the local structure. We show the usefulness of the method in ground-motion studies where both near-field source effects and local site effects are important. Technical problems connected with the inconsistency between the 3D source radiation and the 2D FD calculation are minor for the relatively distant in-plane point explosive sources, but are more serious for the in-plane dislocation sources. 相似文献
32.
Among the three principal regional units of Croatia, i.e. the elongated and spacious Adriatic littoral (with numerous islands), the relatively small and narrow mountainous belt (the Croatian transit doorway) and the Pannonian/peri-Pannonian region, the latter is the largest and accounts for 54 percent of the surface area and 66 percent of the population of Croatia (1991 census). It is part of the Pannonian (or Carpathian) basin, or the central Danube basin, so that Croatia is simply by its position a Danube country. Its Danube character is also highlighted by the fact that the Pannonian/peri-Pannonian region of Croatia through the Sava and Drava Rivers is directly linked to the navigable Danube, which is the historical and ethnic eastern boundary of Croatia. Croatia is an old historical Danube nation and country, although it has nominally appeared as a state after the break-up of Yugoslavia, and its international recognition as an independent state (1992). 相似文献
33.
Václav Vavryčuk 《Pure and Applied Geophysics》1994,143(4):563-586
Complete relations are derived for energy and energy flux of elastic waves generated by an isotropic and double-couple source in a perfectly elastic, homogeneous, isotropic, and unbounded medium. In the energy balance of elastodynamic sources near-field waves play an essential role, transforming static energy into wave energy, andvice versa. For explosive and dislocation sources, the sources surface radiates a positive wave energy that is partially distributed to the medium transforming into static energy. For implosive and antidislocation sources, the source surface generates elastic waves, but it does not necessarily imply that it also radiates a positive wave energy. The energy transported by waves can originate in gradual transformation of the static-to-wave energy during propagation of waves through a stressed medium.On leave from Geophysical Institute, Czech Academy of Sciences, Boní II/1401, 41 31, Praha 4 Czech Republic 相似文献
34.
Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He+ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P 相似文献
35.
Periodic ab initio Hartree-Fock LCAO calculations have been carried out on the two dimensional sheet of SiO4 tetrahedra, representing one of the basic constituting units of layer silicates, using Huzinaga's DZP basis sets. The influence of the basis set on the chemical bonding picture is characterized by Mulliken atomic charges and by electron density maps. Silicon atomic charges +1.6 ¦e¦ are more realistic than those +2.4 ¦e¦ reported for smaller basis sets. The silicon d orbital population is found to be 0.6 in close agreement with molecular data. Electron density maps indicate the absence of charge density in the center of the ditrigonal cavity. The charge buildup of nonbonding basal oxygen orbitals is directed mainly downwards perpendicular to the sheet plane. 相似文献
36.
Weak and strong ground motions were numerically predicted for three stations of the Ashigara Valley test site. The prediction was based on the records from a rock-outcrop station, one weak-motion record from a surface-sediments station, and the standard geotechnical model. The data were provided by the Japanese Working Group on the Effects of Surface Geology as a part of an international experiment. The finite-difference method for SH waves in a 2-D linear viscoelastic medium (a causalQ model) was employed.Comparison with the real records shows that at two stations the predictions fit better than at the third one. Strangely, the two better predictions were for stations situated at larger distances from the reference rock station (one station was on the surface, the other in a borehole). The strong ground motion (the peak acceleration of about 200 cm s–2) was not predicted qualitatively worse than the weak motion (8 cm s–2). A less sophisticated second prediction (not submitted during the experiment), in which we did not attempt to fit the available weak-motion record at the sedimentary station, agrees with the reality significantly better. 相似文献
37.
Summary A possible relation between the 10-day, 1-month, and 2-month geomagnetic as well as solar activity, characterized by Kp and Wolf's number R, and temperatures measured at the Prague-Klementinum meteorological station in January–February of the years 1932–1987 was sought. It was found that:1) Kp correlates with the temperature in Prague better than Wolf's number R.2) If the QBO phase is taken into account, the correlations improve.3) Even if the correlations improves with increasing length of the subintervals into which the individual winter periods (January-February) were derived, their statistical significance declines. 相似文献
38.
The correlation between the long-term intensity variations of cosmic rays at neutron monitor energies and the LDE index measure of solar flares with long-lasting soft X-ray emissions is reported. Three subsequent solar cycles, 20–22, are taken into account and half-monthly data are analyzed. Possible explanation of this correlation is discussed in terms of the recent concepts of cosmic-ray modulation, in particular with merged interaction regions affecting the cosmic-ray intensity. 相似文献
39.
Stanislav Horník 《GeoJournal》1993,31(4):379-382
Some results of biogeographic research on meadows in the Dyje-Svratka basin in the Czech Republic. The paper shows one example of biogeographic inventory of natural ecosystems in an unflooded meadow in the Dyje-Svratka basin. It is part of the complex physio-geographic research of the Geographic Department of the Masaryk University in Brno aimed at gaining a basis for territorial interpretation of ecological regularities and territorial application of general ecological optimizing principles. A segment of biocenosis of Ulmi-fraxineta carpini has been analyzed (Zlatník 1956).The endeavour of Czech geographers to study geosystems of various dimensions completely gets in the limelight. In question is the understanding of mutual relationship of components of geosystems based on the exchange of mass and energy. There are two ways of studying them: spatial relations or approaches concentrated on processes. In contrast to the above unilateral concept, the endeavour to make the approaches compatible appears rarely. This complex view is made possible by geobiocenologically taken biogeography in papers of Zlatník and Rauer, their students and successors. This paper shows only one example of the results of biogeographic stock-taking of meadows in the Dyje-Svratka basin, indicating relations of eco- and geosystems which confirm the necessity of ecological orientation of the present biogeography and its potential contribution to ecology. 相似文献
40.
Miroslav Krs František Novák Marta Krsová Petr Pruner Jiří Jansa 《Studia Geophysica et Geodaetica》1993,37(4):382-400
Summary This study is a follow up of the investigation of some magnetic properties and metastability of greigite in samples obtained from Miocene claystones in the Kruné hory (Erzgebirge) Piedmont basins (Bohemia). Three different methods of upgrading the smythite were applied; the magnetic properties of the concentrates are compared. The thermal conversion of smythite sets in at 200°C while greigite converts at 250°C. The first intermediate products to be formed are iron sulphides, marcasite clearly dominating over pyrite and pyrrhotite. Apart from a Fe3+ sulphate with a composition of Fe2(SO4)3, oxidation of these sulphides gives rise to -Fe2O3. The result of the subsequent decomposition of the mentioned sulphate is the formation of -Fe2O3, which retains the sulphate structure. The final product of the thermal decomposition at 800°C is -Fe2O3. In the smythite concentrate the conversion to Fe3+ sulphate and -Fe2O3 is about twice as intensive as in greigite. No direct conversion to -Fe2O3 was found. During the thermal process self-reversals of remanence were observed, in various samples as many as four reversals in the temperature interval from 340 to 590°C. The occurrences of self-reversals of remanence were only observed at high degrees of thermal demagnetization, of the order of 10–2 down to 10–3 in the temperature interval of sulphide origin (below 400°C), and of the order of 10–4 down to 10–6 in the temperature interval of Fe-oxides origin (above 400°C).Presented at the 3rd Conference on New Trends in Geomagnetism, Castle of Smolenice, Czechoslovakia, June 22–29, 1992 相似文献