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Bohuslav R??ek Jaroslava Plomerová Vladislav Babu?ka 《Studia Geophysica et Geodaetica》2012,56(1):107-140
Joint inversion of teleseismic P-waveforms and local group velocities of surface waves retrieved from ambient seismic noise
has been performed to model velocity structure of the crust and uppermost mantle of the Bohemian Massif. We analysed P-waveforms
of 381 teleseismic earthquakes recorded at 54 broadband seismic stations located on the territory of the Czech Republic and
in its close surroundings. Group velocities of Rayleigh and Love surface waves were obtained by cross-correlating long-term
recordings of seismic noise. The basis for waveform inversion is the well-known methodology of P-to-S receiver functions constructed
from converted phases. Due to instabilities in direct inversion of receiver functions caused by the necessity of applying
deconvolution, we propose an alternative formulation to fit observed and calculated radial components of P waveforms. The
joint inversion is transformed into a search for the minimum of the cost function defined as a weighted sum of waveform and
group velocity misfits. With the use of the robust stochastic optimizer (Differential Evolution Algorithm), neither derivatives
nor a starting model are needed. The task was solved for 1D layered isotropic models of the crust and the uppermost mantle.
We have performed a sequence of inversions with models containing one, two, three and four layers above a half-space. By using
statistical criteria (F-test) we were able to select the simplest velocity models satisfying data and representing local geological
structures. Complex crustal models are typical for stations located close to boundaries of major tectonic units. The relatively
low average P to S wave-velocity ratio is in agreement with the generally accepted view that the BM crust is predominantly
felsic. 相似文献
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Růžek Bohuslav Zedník Jan Klíma Karel Ruprechtová Libuše 《Studia Geophysica et Geodaetica》2000,44(2):175-187
The routine location of regional seismic events using data from the Czech National Seismological Network (CNSN) is based on Pn, Pg, Sn, Sg phases. A simple velocity model derived from Kárník's (1953) interpretation of an earthquake in Northern Hungary in 1951 has hitherto been used. At present, numerous local seismic networks record and locate local events, which are occasionally recorded at regional distances as well. Due to the relatively small dimensions of local networks, hypocenters (and origin times) determined by a local network might be considered as nearly exact from the point of view of regional-scale CNSN. The comparison of common locations performed by CNSN and by a local network enables us to estimate the accuracy of CNSN locations, as well as to optimize a simple velocity model. The joint interpretation of the CNSN bulletin and the catalogues of four local seismic networks WEBNET, OSTRAVA, KLADNO and LUBIN produced a new ID velocity model. The most frequent epicentral error in this model is less than 5 km, and most foci lie up to 15 km from the true position. The performed analysis indicates bimodal distribution of Sn residuals. 相似文献
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Miroslav Novotný Zuzana Skácelová Jan Mrlina Bedřich Mlčoch Bohuslav Růžek 《Surveys in Geophysics》2009,30(6):561-600
The refraction data from the SUDETES 2003 experiment were used for high-resolution tomography along the profile S01. The S01
profile crosses the zone Erbendorf-Vohenstrauss (ZEV) near the KTB site, then follows the SW–NE oriented Eger Rift in the
middle part and continues toward the NE across the Elbe zone and the Sudetic structures as far as the Trans-European Suture
Zone. To get the best resolution in the velocity image only the first arrivals of Pg waves with minimum picking errors were
used. The previous depth-recursive tomographic method, based on Claerbout’s imaging principle, has been adapted to perform
the linearized inversions in iterative mode. This innovative DRTG method (Depth-Recursive Tomography on Grid) uses a regular
system of refraction rays covering uniformly the mapped domain. The DRTG iterations yielded a fine-grid velocity model with
a required level of RMS travel-time fit and the model roughness. The travel-time residuals, assessed at single depth levels,
were used to derive the statistical lateral resolution of “lens-shaped” velocity anomalies. Thus, for the 95% confidence level
and 5% anomalies, one can resolve their lateral sizes from 15 to 40 km at the depths from 0 to 20 km. The DRTG tomography
succeeded in resolving a significant low-velocity zone (LVZ) bound to the Franconian lineament nearby the KTB site. It is
shown that the next optimization of the model best updated during the DRTG iterations tends to a minimum-feature model with
sweeping out any LVZs. The velocities derived by the depth-recursive tomography relate to the horizontal directions of wave
propagation rather than to the vertical. This was proved at the KTB site where pronounced anisotropic behavior of a steeply
tilted metamorphic rock complex of the ZEV unit has been previously determined. Involving a ~7% anisotropy observed for the
“slow” axis of symmetry oriented coincidentally in the horizontal SW–NE direction of the S01 profile, the DRTG velocity model
agrees fairly well with the log velocities at the KTB site. Comparison with the reflectivity map obtained on the reflection
seismic profile KTB8502 confirmed the validity of DRTG velocity model at maximum depths of ~16 km. The DRTG tomography enabled
us to follow the relationship of major geological units of Bohemian Massif as they manifested in the obtained P-wave velocity
image down to 15 km. Although the contact of Saxothuringian and the Teplá-Barrandian Unit (TBU) is collateral with the S01
profile direction, several major tectonic zones are rather perpendicular to the Variscan strike and so fairly imaged in the
S01 cross-section. They exhibit a weak velocity gradient of sub-horizontal directions within the middle crust. In particular,
the Moldanubian and TBU contact beneath the Western Krušné hory/Erzgebirge Pluton, the buried contact of the Lusatia unit
and the TBU within the Elbe fault zone were identified. The maxima on the 6,100 ms−1 isovelocity in the middle crust delimitated the known ultrabasic Erbendorf complex and implied also two next ultrabasic massifs
beneath the Doupovské hory and the České středohoří volcanic complexes. The intermediate mid-crustal P-wave velocity lows
are interpreted as granitic bodies. The presented geological model is suggested in agreement with available gravity, aeromagnetic
and petrophysical data. 相似文献
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The paper presents some results of seismic experiments carried out on the territory of northern Moravia and Silesia, roughly
delimited by the coordinates 16°E–19°E and 49°N–51°N. The experiments were aimed at compiling a velocity model of the uppermost
Earth’s crust using the database of arrival times of Pg and Sg waves recorded at a fairly large number of seismic stations, which enabled us to produce a simple 1D-layered velocity model
of the region. The velocity model was computed using the traditional tomographic iterative process composed of consecutive
solutions of linear equations. Based on the analysis of velocity distribution, it was found that the velocities of Pg and Sg waves increase from about 5.9 and 3.3 km/s at the surface, to about 6.1 and 3.5 km/s at a depth of 11 km, respectively. 相似文献
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All recent available data sets containing traveltimes of Pg and Sg phases for the Moravo-Silesian region were collected. These
data come from several experiments designed mostly in 2D (in-line) configurations. Simultaneous processing of all data is
possible only considering the true 3D measurement geometry. The goal of this work is to establish the representative 3D seismic
model by means of seismic tomography. The resulting minimum-structure model is presented in a simple and easy to use form
on the Internet. The amount of processed data is relatively low but repeating the computations with new experimental data
included would be very easy. Important material related to this paper is placed on web pages. 相似文献
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Milan Nov��k Petr Gadas Jan Filip Tom��? Vaculovi? Jan P?ikryl Bohuslav Fojt 《Mineralogy and Petrology》2011,102(1-4):3-14
Syn-tectonic quartz-calcite veins containing blue beryl are enclosed in hematite > magnetite-rich portions of the low-grade metamorphosed Fe-deposit Skály near Ryma?ov, Czech Republic. Aggregates of pale to deep blue beryl, up to 2?cm in diameter, are associated with euclase, clinochlore, hematite, albite and dravite. Complexly zoned beryl crystals consist of skeletal aggregates of beryl I randomly distributed within volumetrically dominant beryl II with narrow rims of beryl III. All types of beryl have similar contents of Na (0.32?C0.49 apfu) and Mg (0.31?C0.41 apfu) but variable contents of Fetot (0.05?C0.34 apfu) and Al (1.20?C1.62 apfu). The LA-ICP-MS study yielded elevated contents of Li, up 1,314?ppm (0.28?wt.% Li2O) in beryl I. The quartz-calcite veins represent an unusual type of low-T metamorphic-hydrothermal vein related to Fe-ore deposit characterized by single-stage fracturing and mobilization in a closed system at T~200?C300°C and CO 3 2- as a major complexing agent for the mobility of Be. 相似文献
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Mine excavation in deep black-coal Mayrau Mine, Czech Rep., has a pronounced 7-day periodicity due to the absence of mining during weekend days. Also seismicity induced by mining exhibits some features of the 7-day period. It was found that the number of events generally depends on the intensity of mining, while the analogous dependences of mean energy per event and the total energy per day are weaker. Selective analysis showed that total extent of exploitation has more influences on the seismicity than coining of drifts. The statistical parameters of seismicity (b-value) do not change in accordance with the day of the week. 相似文献
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Zdeněk Dolníček Bohuslav Fojt Walter Prochaska Jan Kučera Petr Sulovský 《Mineralium Deposita》2009,44(1):81-97
The Zálesí vein-type deposit is hosted by Early Paleozoic high-grade metamorphic rocks on the northern margin of the Bohemian
Massif. The mineralization is composed of three main stages: uraninite, arsenide, and sulfide. The mineral assemblages formed
at low temperatures (~80 to 130°C, locally even lower) and low pressures (<100 bars). The salinity of the aqueous hydrothermal
fluids (0 to 27 wt.% salts) and their chemical composition vary significantly. Early fluids of the oldest uraninite stage
contain a small admixture of a clathrate-forming gas, possibly CO2. Salinity correlates with oxygen isotope signature of the fluid and suggests mixing of brines [δ
18O around +2‰ relative to standard mean ocean water (SMOW)] with meteoric waters (δ
18O around −4‰ SMOW). The fluid is characterized by highly variable halogen ratios (molar Br/Cl = 0.8 × 10−3 to 5.3 × 10−3; molar I/Cl = 5.7 × 10−6 to 891 × 10−6) indicating a dominantly external origin for the brines, i.e., from evaporated seawater, which mixed with iodine-enriched
halite dissolution brine. The cationic composition of these fluids indicates extensive interaction of the initial brines with
their country rocks, likely associated with leaching of sulfur, carbon, and metals. The brines possibly originated from Permian–Triassic
evaporites in the neighboring Polish Basin, infiltrated into the basement during post-Variscan extension and were finally
expelled along faults giving rise to the vein-type mineralization. Cenozoic reactivation by low-salinity, low-δ
18O (around −10‰ SMOW) fluids of mainly meteoric origin resulted in partial replacement of primary uraninite by coffinite-like
mineral aggregates. 相似文献