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Libor Šachl 《Studia Geophysica et Geodaetica》2013,57(1):84-102
The first-order Born approximation is a weak scattering perturbation method which is a powerful tool. The combination of the Born approximation and the ray theory enables to extend the applicability of the ray theory in terms of the required smoothness of the model and ensures faster computations than with, e.g., the finite difference method. We are motivated to describe and explain the effects of the numerical discretization of the Born integral on the resulting seismograms. We focus on forward modelling and study the cases in which perturbation from the background model contains the interface. We restrict ourselves to isotropic models that contain two homogeneous layers. We compare the 2D and 3D ray-based Bornapproximation seismograms with the ray-theory seismograms. The Born seismograms are computed using a grid of finite extent. We anticipate that the computational grid should contain an appropriate number of gridpoints, otherwise the seismogram would be inaccurate. We also anticipate that the limited size of the computational grid can cause problems. We demonstrate numerically that an incorrect grid can produce significant errors in the amplitude of the wave, or it can shift the seismogram in time. Moreover, the grid boundaries work as interfaces, where spurious waves can be generated. We also attempt to explain these phenomena theoretically. We give and test the options of removing the spurious waves. We show that it is possible to compute the Born approximation in a sparser grid, if we use elastic parameters averaged from some dense grid. 相似文献
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Jiří Málek Oldřich Novotný Renata Gaždová Libor Žanda 《Studia Geophysica et Geodaetica》2010,54(3):389-401
The Orlík water reservoir was built on the Vltava River in the places where the river crosses the geological unit called the Central Bohemian Pluton. Previous geological studies have disclosed no significant lateral inhomogeneity or fault zone in the close vicinity of the reservoir. However, repeated levellings, performed there in the 1950s and 1960s, revealed a systematic subsidence of the Vltava River valley. Using these measurements, the idea of the tectonic origin of the valley was even formulated. Recent seismic observations have also attracted attention to this region. Namely, a macroseismically felt earthquake occurred there on January 13, 2007, and many weaker earthquakes have been recorded by local seismic networks since 1992. To increase the accuracy of locating these seismic events, recently we have carried out refraction measurements along a short profile across the Orlík reservoir. These authors smoothed the observed travel times and derived a 1-D velocity model of the shallow crustal structure for the Orlík region. In the present paper, using the same refraction measurements, we study some anomalies in wave propagation beneath the Orlík reservoir. In particular, it is shown that the passage of seismic waves beneath the reservoir leads to their time delays and spectral changes. Moreover, we have also recognised similar time delays in earlier data from the nearby international profile CEL09 in the places where the profile crosses the Orlík reservoir. 相似文献
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Utilization of a new geomorphometric variable for land surface segmentation — the angle of absolute curvatures — is a main goal of the paper. The angle of absolute curvatures is defined as the difference between the orientation of maximal curvature (field independent) and the orientation of the greater of the profile or the tangential curvature. Land-forms separated by three types of borders (A, B, C) can be delimited from the field of angles of absolute curvatures. Borders of A type are connected with a local extreme of slope. Borders of B and C type are connected with a change to the priority of either profile or tangential curvature, as shown in computation, respectively. Fields of altitude, slope, profile curvature, tangential curvature and rotor curvature are reflected by an algorithm. Distinct borders in the field of the angles of absolute curvatures are connected with a sudden change of value and with zero isolines in the previously mentioned fields. Spatially closed entities generated by this proposed algorithm are considered to be a variant of the elementary forms of the land surface. The quality of information generated by this algorithm depends on the size of the grid mesh of the input digital elevation model. The algorithm in its current state is suitable for locating the borders of some elementary forms in the first stage of geomorphology mapping. 相似文献
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Peter Maas Rudolf Ondrasik Libor Jansky 《山地科学学报》2005,2(3):202-210
The Western Carpathians are located out of world main natural hazardous zones. Human casualties are related more to snow avalanches in connection with mountain hiking, some individuals yearly by flooding and rarely by forest fires. Economic lost about 0.1 to 0.2 %, exceptionally up to 0.8 % of the gross domestic product （GDP） proportionally to the Carpathian regions of particular countries. Natural disasters are linked, except of the above mentioned events, to infrequent small and medium scale earthquakes, landslides, and erosion. Records of the most harmful natural events are found in archives since the 16^th century. Their systematic study and factor analysis started from the end of the 19^th century, and protective measures and organization of impact mitigation developed during the 20^th century to minimize the risk. 相似文献
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The Lateglacial and Holocene in Central Europe: a multi‐proxy environmental record from the Bohemian Forest,Czech Republic 
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下载免费PDF全文 Klára Vočadlová Libor Petr Pavla Žáčková Marek Křížek Lenka Křížová Simon M. Hutchinson Miroslav Šobr 《Boreas: An International Journal of Quaternary Research》2015,44(4):769-784
The Hercynian mountain ranges were islands of mountain glaciation and alpine tundra in a Central European ice‐free corridor during the Late Pleistocene. Today they are notable areas of glacial landforms, alpine‐forest free areas, peatlands and woodlands. However, our knowledge of the Lateglacial and early Holocene environmental changes in this region is limited. We present a new multi‐proxy reconstruction of a mid‐altitude environment in the Bohemian Forest spanning this period. A core (5.2 m length) in the ?erné Lake cirque (1028 m a.s.l.) was subjected to lithological, geochemical, pollen and macrofossil analysis supplemented by two optically stimulated luminescence (OSL) and 10 AMS radiocarbon dates. We determined the impact of regional and supraregional climate changes on the environment. The two most significant changes in sedimentation during the Lateglacial (17.6 and 15.8–15.5 cal. ka BP) were synchronous with regional glacial chronostratigraphy. Unlike Central European mountain ranges, in the Bohemian Forest the Younger Dryas was not coincident with glacier re‐advance, but was a dry, cold episode with low lake levels, which prevailed until the early Preboreal. Plant macrofossils indicate local establishment of Betula nana and Betula pendula/pubescens at 15.4–13.4 cal. ka BP. Comparison with Holocene records from Central Europe shows a similar immigration history of vegetation at mid and higher altitudes. The tree line exceeded an altitude of ~1000 m a.s.l. around 10.5 cal. ka BP and coincided with rapid geochemical changes in the sediment. The 8.2 ka BP event did not have any response in the sedimentary record, but corresponded to stabilization of the Picea abies population and expansion of Fagus. Fagus colonized the Bohemian Forest earlier than other Hercynian mid‐mountains, but never predominated in the composition of the forest at higher elevations. Abies alba was the last tree species that immigrated to the study area. 相似文献
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Assessment of satellite-based rainfall estimates in urban areas in different geographic and climatic regions 总被引：1，自引：0，他引：1
This paper presents an assessment of the 3B42 research version rainfall product from NASA’s Tropical Rainfall Measuring Mission
Multi-satellite Precipitation Analysis (TMPA). The study provides new results of TMPA data accuracy in urban areas and highlights
trends associated with the climatological indicators of temperature and relative humidity in cities. Ten years (1998-2007)
of TMPA data were analyzed for three case study cities in the United States (Houston, Atlanta, and Las Vegas) and one in Korea
(Cheongju), representing semi-arid to humid climates. At each location, an urbanized river basin and non-urbanized river basin
were selected and comparisons between TMPA and rain gage observations were made for recorded storm events in the study period,
the largest storm events by total depth, and selected hurricanes and topical storms. The results indicate TMPA data match
well with rain gage observations at all locations. TMPA is slightly underestimated for semi-arid regions and overestimated
for humid regions. The relative magnitude of TMPA rain event accumulation compared to rain gage accumulation is noted to be
smaller for urbanized watersheds and high intensity events. The correlation of TMPA accuracy with temperature and relative
humidity and the analysis of accuracy by season indicate TMPA is more accurate for convective rainfall events. This suggests
a possible linkage between the observed urban-modified temperatures, hypothesized enhanced convection, and improved TMPA accuracy
in urban areas. 相似文献
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We analyze refraction measurements along a short profile in western Kru?né hory crystalline unit. The profile passed close to the seismically active zone of Nový Kostel. The measurements were carried out to distances of about 15 km using quarry blasts near the village of Horní Rozmy?l, located at the eastern margin of the crystalline unit. Smoothed P-wave travel times were interpreted using the Wiechert-Herglotz method, which yielded a 1-D velocity model of the shallow crustal structure of the crystalline unit down to a depth of 1.7 km. The P-wave velocity of the model increases from about 4.0 km/s at the surface to 5.9 km/s at a depth of 1.7 km. The superficial velocities of our model are somewhat higher than the superficial velocities of the model that is routinely used for earthquake location in the region. 相似文献
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Jitka &#x;pi
kov Irena Dobe&#x;ov Marek Vach Petr Sk&#x;ivan Martin Mihaljevi
Milo&#x; Burian 《Chemie der Erde / Geochemistry》2008,68(1):105-115
Atmospheric precipitation samples were collected in the Bohemian Karst (30 km SW from Prague, Czech Republic) at six localities in the vicinity of the limestone-quarry Čertovy schody during years 1996–2003. Samples were analyzed for major components (Na+, K+, Mg2+, Ca2+, F−, Cl−, NO3−, HCO3−, SO42−) and trace metals (Cu, Mn, Fe, Zn, Pb, Be, As, Sr, Cd, Al, Cr). Deposition fluxes were calculated from more than 10 000 elemental analyses of samples collected monthly. The fluxes of monitored substances show temporal and spatial variability. The most marked attribute is the strong affection by local emission sources confirmed by the investigation of seasonal variability, temporal trend and correlation analysis. 相似文献
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René Hudec Pavel Spurný Jan Florián Jaroslav Boček Miloš Tichý Jana Tichá Libor Vyskočil Wolfgang Wenzel Scott Barthelmy Thomas Cline Niels Gehrels Gerald Fishman Chryssa Kouveliotou Charles Meegan Asen Mutafov 《Experimental Astronomy》1997,7(4):319-323
We present first preliminary results obtained with the European Observation Network consisting of 9 observatories in the Czech Republic, Germany and Bulgaria. We also discuss related problems such as the background of unknown variable stars and suggest a strategy for work in this area. 相似文献
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