Attenuation ofSH waves before cut-off frequency     

Karel Pêê 《Studia Geophysica et Geodaetica》1964,8(2):140-147

  相似文献   

Theorie der im elastischen halbraum durch eine flächenförmige quelle erregten wellen. (1. teil)     

Pěč  Karel 《Studia Geophysica et Geodaetica》1959,3(2):135-153

Studia Geophysica et Geodaetica - В работе рассматривается...  相似文献   

Geophysical Field Pattern in The West Bohemian Geodynamic Active Area     

Švancara  Jan  Gnojek  Ivan  Hubatka  František  Dědáček  Karel 《Studia Geophysica et Geodaetica》2000,44(2):307-326

Regional geophysical data from detailed gravity survey, airborne magnetometry and gamma-ray spectrometry were analysed in order to determine the subsurface extent of contrasting geological bodies and to highlight subtle anomalies which can be related to the occurrence of earthquake swarms. Potential field data were compiled into contour and colour-shaded relief maps suitable for detecting structural tectonic elements. A shaded relief map of the horizontal gradient of gravity was used to detect considerable structural and tectonic features. The results of airborne gamma-ray spectrometry, showing the regional total gamma-ray activity, abundance of uranium, thorium and potassium, were included in this study. Only the two most instructive maps – the total gamma-ray activity and the abundance of potassium are shown. The main line of epicentres Nový Kostel – Poátky coincides well with the N-S configuration of abundances of these natural radioactive elements. The epicentres of micro-earthquakes detected by the local seismological network KRASLICE for the 1991 to 1998 period were plotted in the geophysical maps. The hypocentres of earthquakes in the main epicentral zone at Nový Kostel were projected onto the crustal density model based on the interpretation of seismic reflection profile 9HR and gravity data. The average distance between the Nový Kostel epicentral zone and the seismic profile was 4-5 km. Based on the interpretation of gravity data the hypocentres of the main epicentral zone seem to be associated with the western margin of the Eibenstock - Nejdek (Karlovy Vary) Pluton and, beside that, they follow the depth level where the allochthonnous part of the Saxothuringian Zone is thrust over the European parautochton. A drawing of the geodynamic model of the area is also shown.  相似文献   

Thermal and mechanical behaviour of the orogenic middle crust during the syn‐ to late‐orogenic evolution of the Variscan root zone,Bohemian Massif     

B. Petri  P. Štípská  E. Skrzypek  K. Schulmann  M. Corsini  J. Franěk 《Journal of Metamorphic Geology》2014,32(6):599-626

We combine structural observations, petrological data and ⁴⁰Ar–³⁹Ar ages for a stack of amphibolite facies metasedimentary units that rims high‐P (HP) granulite facies felsic bodies exposed in the southern Bohemian Massif. The partly migmatitic Varied and Monotonous units, and the underlying Kaplice unit, show a continuity of structures that are also observed in the adjacent Blanský les HP granulite body. They all exhibit an earlier NE?SW striking and steeply NW‐dipping foliation (S3), which is transposed into a moderately NW‐dipping foliation (S4). In both the Varied and Monotonous units, the S3 and S4 foliations are characterized by a Sil–Bt–Pl–Kfs–Qtz–Ilm±Grt assemblage, with occurrences of post‐D4 andalusite, cordierite and muscovite. In the Monotonous unit, minute inclusions of garnet, kyanite, sillimanite and biotite are additionally found in plagioclase from a probable leucosome parallel to S3. The Kaplice unit shows rare staurolite and kyanite relicts, a Sil–Ms–Bt–Pl–Qtz±Grt assemblage associated with S3, retrogressed garnet?staurolite aggregates during the development of S4, and post‐D4 andalusite, cordierite and secondary muscovite. Mineral equilibria modelling for representative samples indicates that the Varied unit records conditions higher than ~7 kbar at 725 °C during the transition from S3 to S4, followed by a P?T decrease from ~5.5 kbar/750 °C to ~4.5 kbar/700 °C. The Monotonous unit shows evidence of partial melting in the S3 fabric at P?T above ~8 kbar at 740–830 °C and a subsequent P?T decrease to 4.5–5 kbar/700 °C. The Kaplice unit preserves an initial medium‐P prograde path associated with the development of S3 reaching peak P?T of ~6.5 kbar/640 °C. The subsequent retrograde path records 4.5 kbar/660 °C during the development of S4. ⁴⁰Ar–³⁹Ar geochronology shows that amphibole and biotite ages cluster at c. 340 Ma close to the HP granulite, whereas adjacent metasedimentary rocks preserve c. 340 Ma amphibole ages, but biotite and muscovite ages range between c. 318 and c. 300 Ma. The P?T conditions associated with S3 imply an overturned section of the orogenic middle crust. The shared structural evolution indicates that all mid‐crustal units are involved in the large‐scale folding cored by HP granulites. The retrograde P–T paths associated with S4 are interpreted as a result of a ductile thinning of the orogenic crust at a mid‐crustal level. The ⁴⁰Ar–³⁹Ar ages overlap with U–Pb zircon ages in and around the HP granulite bodies, suggesting a short duration for the ductile thinning event. The post‐ductile thinning late‐orogenic emplacement of the South Bohemian plutonic complex is responsible for a re‐heating of the stacked units, reopening of argon system in mica and a tilting of the S4 foliation to its present‐day orientation.  相似文献   

Types of soft-sediment deformation structures in a lacustrine Ploužnice member (Stephanian,Gzhelian, Pennsylvanian,Bohemian Massif), their timing,and possible trigger mechanism     

Marcela Stárková  Karel Martínek  Radek Mikuláš  Nicholas Rosenau 《International Journal of Earth Sciences》2015,104(5):1277-1298

  相似文献   

Evaluation of meteorological controls of reconstructed rockfall activity in the Czech Flysch Carpathians     

Karel Šilhán  Rudolf Brázdil  Tomáš Pánek  Petr Dobrovolný  Lucie Kašičková  Radim Tolasz  Ondřej Turský  Marek Václavek 《地球表面变化过程与地形》2011,36(14):1898-1909

Rockfall is an important process in the final sculpturing of escarpments and scree slopes that originate in bedrock landslides in the Flysch Carpathians. The spatio‐temporal characteristics of rockfall activity were studied at four localities representative of old landslides in the highest part of the Czech Flysch Carpathians (Moravskoslezské Beskydy Mountains). Historical activity, chronology, and spatial context of rockfall activity were reconstructed using dendrogeomorphic techniques and rockfall rate index (RR). A total of 1132 increment cores from 283 trees growing in the rockfall transport and accumulation zones enabled the dating of 989 rockfall events. Reconstruction of a 78‐year‐long RR chronology suggests similar rockfall histories and trends at all study sites, indicating the existence of major common factors driving rockfall dynamics in the region. Temporal analysis and correlation of the RR series obtained with monthly mean temperatures, numbers of days with temperature transitions through 0 °C and monthly precipitation totals show that meteorological characteristics have evident but variable influence on rockfall activity. The most important factor is the effect of freeze–thaw cycles throughout the year, supplemented by low temperatures, especially during autumn. The influence of precipitation totals is of lesser importance. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Origin of freshwater and polynya water in the Arctic Ocean halocline in summer 2007     

Dorothea Bauch  Michiel Rutgers van der Loeff  Nils Andersen  Sinhue Torres-Valdes  Karel Bakker  E. Povl Abrahamsen 《Progress in Oceanography》2011,91(4):482-495

Extremely low summer sea-ice coverage in the Arctic Ocean in 2007 allowed extensive sampling and a wide quasi-synoptic hydrographic and δ¹⁸O dataset could be collected in the Eurasian Basin and the Makarov Basin up to the Alpha Ridge and the East Siberian continental margin. With the aim of determining the origin of freshwater in the halocline, fractions of river water and sea-ice meltwater in the upper 150 m were quantified by a combination of salinity and δ¹⁸O in the Eurasian Basin. Two methods, applying the preformed phosphate concentration (PO^*) and the nitrate-to-phosphate ratio (N/P), were compared to further differentiate the marine fraction into Atlantic and Pacific-derived contributions. While PO^*-based assessments systematically underestimate the contribution of Pacific-derived waters, N/P-based calculations overestimate Pacific-derived waters within the Transpolar Drift due to denitrification in bottom sediments at the Laptev Sea continental margin.Within the Eurasian Basin a west to east oriented front between net melting and production of sea-ice is observed. Outside the Atlantic regime dominated by net sea-ice melting, a pronounced layer influenced by brines released during sea-ice formation is present at about 30–50 m water depth with a maximum over the Lomonosov Ridge. The geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the Transpolar Drift.The ratio of sea-ice derived brine influence and river water is roughly constant within each layer of the Arctic Ocean halocline. The correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea-ice formation within the Arctic Ocean. Over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found, sea-ice formation results in a linear correlation between brine influence and river water at salinities of about 32–34. In coastal polynyas in the shallow regions of the Laptev Sea and southern Kara Sea, sea-ice formation transports river water into the shelf’s bottom layer due to the close proximity to the river mouths. This process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30–32. Our study indicates which layers of the Arctic Ocean halocline are primarily influenced by sea-ice formation in coastal polynyas and which layers are primarily influenced by sea-ice formation over the open ocean. Accordingly we use the ratio of sea-ice derived brine influence and river water to link the maximum in brine influence within the Transpolar Drift with a pulse of shelf waters from the Laptev Sea that was likely released in summer 2005.  相似文献   

Book reviews     

G. Kunkel  Barry Floyd  John Innes  Daniel W. Oade  V. Kamiuske  K. Pye  Karel Bayer  B. Schulze  Mohammad A. Kishk  Wolf Tietze 《GeoJournal》1990,22(1):107-108

  相似文献   

The Roermond earthquake of 13 April 1992, the Netherlands: geological aspects     

Vladimir G. Trifonov  Jean Klerkx  Karel Theunissen 《地学学报》1994,6(3):301-305

The epicentre of the Roermond earthquake is located near the western boundary fault of the Roer valley trough, one of the deepest and the most active in the Quaternary part of the Lower Rhine graben. The Late Pleistocene and Holocene activity of the trough is manifested by offsets of the main (Mindel) and the lower (Riss and Late Pleistocene) terraces along the boundary faults.
Surface fractures have been observed in an area of more than 50 km²: 2.5–3.5 km to the north of the town of Roermond, at 0.8 km to the south of the village of Herkenbosch and in the southeastern part of the village of Montfort. Three types of ruptures were differentiated: scarps up to 50 cm high along open fractures near the Maas River; open fractures (continued by scarps in some places) and open fractures with a liquefaction of the Quaternary alluvium sands. The last type is predominant. The location of the ruptures depends on the landscape and water-table of the region. While they could be produced solely by hydraulic shock during the earthquake (increased by the wet spring season), the majority of the ruptures strike N50°W ± 10°, i.e. parallel to the main trough faults, or N55°E ± 10°, along 'neotectonic lines', parallel to the Maas valley and deduced from space imagery. Thus, the ruptures could be the secondary surficial effect of the earthquake, linked indirectly with the active tectonics of the region.  相似文献   

Intergranular diamonds derived from partial melting of crustal rocks at ultrahigh-pressure metamorphic conditions     

Andrey V. Korsakov  Karel Theunissen  Larissa V. Smirnova 《地学学报》2004,16(3):146-151

By reporting for the first time intergranular diamond in quartz–feldspar (Qtz–Kfs) aggregates, the processes of metamorphic diamond formation have to be reconsidered. Based on their Kfs/Qtz ratio, the texture of these aggregates are proposed to result from ‘granitic’ melt with a calculated composition that corresponds well with that of experimental data for the pelitic system. Taking into account experiments on CO₂ solubility in silicate melt under ultrahigh‐pressure conditions, a granitic melt is further suggested to act as a crystallization medium as well as a transport medium for producing metamorphic diamond.  相似文献