Migration of earthquake foci in Europe     

Dana Procházková 《Pure and Applied Geophysics》1973,110(1):2005-2011

Summary The present paper deals with the migration of earthquake foci in the horizontal and vertical plane observed in Europe and Asia Minor in the period 1901–69.  相似文献   

Distribution of earthquake sequences in the Mediterranean     

Dana Procházková 《Pure and Applied Geophysics》1973,111(1):2158-2162

Summary The results that were obtained by the study of space distribution of individual types of earthquake sequences in the Mediterranean are summarized. The present results apply only to large earthquakes, because with weak shocks it is not possible to present reliable results owing to the incompleteness of material.  相似文献   

Test of differences of magnitude-frequency relation parameters due to different calculation procedures     

Dana Procházková 《Pure and Applied Geophysics》1974,112(4):727-736

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Migration of strong intermediate earthquakes from depth to surface     

Dana Procházková  Reviewer J. Buben 《Studia Geophysica et Geodaetica》1972,16(4):404-406

Zusammenfassung Für den überwiegenden Teil der Gebiete mitteltiefer Erdbeben ist eine Verschiebung der Herde starker Erschütterungen aus der Tiefe zur Oberfläche hin in bestimmten Zeitintervallen charakteristisch. Am Ende einer Sequenz mitteltiefer Erschütterungen, deren Tiefe sich mit der Zeit verkleinert, kommt gewöhnlich in demselben Gebiet ein starkes Erdbeben nahe an der Erdoberfläche vor.

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Dedicated to Academician Alois Zátopek on His 65th Birthday  相似文献   

Quaternary Listserver Newsgroup     

Dana L. Naldrett 《Journal of Paleolimnology》1995,13(3):291-292

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Compositional variation of coexisting olivine,orthopyroxene and Fe/Mg-ferrite as a function of T and f_{O_2 }: a geothermometer and oxygen-barometer     

A. Dana Johnston  John R. Beckett 《Contributions to Mineralogy and Petrology》1986,94(3):323-332

A thermodynamic model is developed that describes the compositional variation of coexisting olivine, orthopyroxene, and ferrite (Fe₃O₄-MgFe₂O₄) as a function of and T. The ferrite phase has a cation distribution which varies from nearly inverse to nearly random with increasing T and is described with a model in which the number of sites per formula unit on which mixing occurs varies from 1.67 to 2.0. Given this model and the equilibrium phase composition data for coexisting olivine and ferrite at 1,300° C of Jamieson and Roeder (1984), the ferrite solution is described to an excellent approximation by a symmetric regular solution model with W _ft =+14.0 ±0.3 kJ/mole. Orthopyroxene and olivine non-ideality are also considered. The T-dependence of the equilibrium constant for the oxidation reaction 6Fs+2Mt=6Fa+O₂ and the two Fe/Mg exchange reactions between olivine-ferrite and olivine-orthopyroxene, are used to calculate the compositional variation of coexisting phases as a function of and T. The results are summarized on an isobaric (1 bar) –1/Tplot with the compositional variation of olivine, ferrite, and orthopyroxene shown by sets of isopleths. The ferrite isopleths intersect those of olivine and orthopyroxene at sufficiently high angles for this assemblage to serve as a sensitive geothermometer and oxygen-barometer. The model is applied to orthopyroxene-ferrite symplectite in coronas around olivine in a metamorphosed gabbro, to olivine-hosted orthopyroxene-ferrite symplectite in unmetamorphosed gabbros and norites and to olivine-hosted orthopyroxene-ferrite symplectites developed within the rims of lherzolite xenoliths.  相似文献   

Dunes of the Gran Desierto Sand-Sea,Sonora, Mexico     

N. Lancaster  R. Greeley  P. R. Christensen 《地球表面变化过程与地形》1987,12(3):277-288

The Gran Desierto Sand-Sea contains dunes of crescentic and star form in simple, compound, and complex varieties. The dunes have developed in bimodal to complex wind regimes of intermediate energy. Transitions from simple through compound to complex crescentic dunes are associated with regional changes in wind regimes. Growth of large star dunes takes place by merging of smaller crescentic and reversing dunes from southerly directions and reworking of sand by northerly and westerly winds. Although wind regimes appear to be the major control of dune morphology in this sand-sea, there is a close correlation between the spacing of simple crescentic dunes and the grain size of the coarse 20th percentile.  相似文献   

Magnitudes of detectable and localizable shocks in nw bohemia     

Vladimír Tobyáš  Jaroslav Fiedler  Dana Knaislová  Dana Procházková  Reviewer I. Pšenčík 《Studia Geophysica et Geodaetica》1985,29(1):68-74

Summary The effectiveness of recording seismic phenomena in the Kruné hory (Mts.) region in NW Bohemia by selected stations in the CSR, GDR and Poland has been estimated. Magnitude isolines of the weakest earthquakes, which can be localized and detected with an 0.9 probability, were calculated on the basis of the level of seismic disturbances at the individual stations and of the empirical dependence of the attenuation of seismic waves with distance.

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Radon-222 Concentration and Aquifer Lithology in North Carolina   总被引：1，自引：0，他引：1  

Dana P. Loomis 《Ground Water Monitoring & Remediation》1987,7(2):33-39

The presence of the radioactive gas radon (Rn-222) in many ground water supplies is a potentially significant source of public exposure to ionizing radiation. A wide range of radon concentrations has been measured in ground water in North Carolina, including some far in excess of national average concentrations. North Carolina is, however, geologically complex and ground water radon concentrations vary considerably among the state's aquifers. The highest average radon concentrations occur in areas underlain by granites (geometric mean 5910 pCi/l), and the lowest occur in the Atlantic Coastal Plain region (48 pCi/l). Average radon levels intermediate between these extremes are characteristic of the large areas of North Carolina underlain by gneisses, schists and metavolcanic rocks. Relative average radon concentrations in ground water from the rock types surveyed are consistent with relative abundances of uranium, the parent element of radon, in these rocks. Although other geologic and hydrologic factors also have an effect, aquifer lithology is a useful predictor of the concentration of radon in ground water. The occurrence of high radon concentrations in certain aquifer types; such as granites, shows that geologic factors should be considered in estimates of population exposure to radon, and that knowledge of aquifer geology can help to predict ground water radon concentrations in areas where field sampling has not been done.  相似文献   

Fluid absent melting of a layered crustal protolith: implications for the generation of anatectic granites     

Kjell P. Skjerlie  Alberto E. Patiño Douce  A. Dana Johnston 《Contributions to Mineralogy and Petrology》1993,114(3):365-378

We report the result of H₂O-undersaturated melting experiments on charges consisting of a layer of powdered sillimanite-bearing metapelite (HQ36) and a layer of powdered tonalitic gneiss (AGC150). Experiments were conducted at 10 kbar at 900°, 925° and 950°C. When run alone, the pelite yielded 40 vol% strongly peraluminous granitic melt at 900°C while the tonalite produced only 5 vol% weakly peraluminous granitic melt. At 950°C, the pelite and the tonalite yielded 50 vol% and 7 vol% granitic melt, respectively. When run side by side, the abundance of melt in the tonalite was 10 times higher at all temperatures than when it was run alone. In the pelite, the melt abundance increased by 25 vol%. When run alone, biotite dehydration-melting in the tonalite yielded orthopyroxene and garnet in addition to granitic melt. When run side by side only garnet was produced in addition to granitic melt. Experiments of relatively short duration, however, also contained Al-rich orthopyroxene. We suggest that the large increase in melt fraction in the tonalite is mainly a result of increased activity of Al₂O₃ in the melt, which lowers the temperature of the biotite dehydration-melting reaction. In the pelite, the increase in the abundance of melt is caused by transport of plagioclase component in the melt from the tonalite-layer to the pelite-layer. This has the effect of changing the bulk composition of this layer in the direction of minimum-temperature granitic liquids. Our results show that rocks which are poor melt-producers on their own can become very fertile if they occur in contact with rocks that contain components that destabilize the hydrous phase(s) and facilitate dehydration-melting. Because of this effect, the continental crust may have an even greater potential for granitoid melt production than previously thought. Our results also suggest that many anatectic granites most likely contain contributions from two or more different source rocks, which will be reflected in their isotopic and geochemical compositions.  相似文献