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141.
The attenuation factor QP at the top of the inner core is evaluated by using the amplitude spectral ratio of PKPdf and PKPbc phases observed at African
stations (BGCA mostly), from strong deep earthquakes in the Pacific Ocean area. The maximum depth of penetration of the PKPdf
phase into the inner core (IC) is roughly 377 km, and the sampled region of IC is centered beneath the Southern Indian Ocean.
The derived mean value of QP is 249 ± 31 (95% confidence level) in the frequency range 0.2–2 Hz, where no frequency dependence of attenuation has been
reliably observed. By using Student’s t-test, we show that the value is statistically significantly different (with a probability
greater than 95%) from other mean values of Q derived by using the same method, for both the western (180 °W to 40 °E) and
eastern (40 °E to 180 °E) hemispheres of the IC. The decrease of Q with the radius of the turning point (denoted by rTP), according to QP = 840 − 0.62 rTP, has a moderate statistical support (the R-squared value is 38%). A slightly increase of Q as a function of the angle of
the PKPdf path within the inner core with respect to the Earth’s spin axis is observed, in agreement with various investigations
performed in the time domain. However, the value of the anisotropy, if any, is suggested to be around 3%. 相似文献
142.
143.
Alexey?V.?BorisovEmail author Ivan?S.?Mamaev 《Celestial Mechanics and Dynamical Astronomy》2005,92(4):371-380
We consider integrable spherical analog of the Darboux potential, which appear in the problem (and its generalizations) of
the planar motion of a particle in the field of two and four fixed Newtonian centers. The obtained results can be useful when
constructing a theory of motion of satellites in the field of an oblate spheroid in constant curvature spaces. 相似文献
144.
Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal calc-alkaline magmatism 总被引:63,自引:0,他引:63
Roberto Oyarzun Alvaro Márquez Javier Lillo Ivan López Sergio Rivera 《Mineralium Deposita》2001,36(8):794-798
Cenozoic magmatic activity in northern Chile led to the formation of two contrasting porphyry copper belts: (1) a Paleocene-Early Eocene belt comprising small porphyry copper deposits (e.g., Lomas Bayas) of normal calc-alkaline affinity; and (2) a Late Eocene-Early Oligocene belt hosting huge porphyry copper deposits (e.g., Chuquicamata) of adakitic affinity. Although the first belt comprises both volcanic and plutonic rocks (andesitic-basaltic and rhyolitic lavas and tuffs, and associated sub-volcanic porphyries and felsic stocks), the latter only includes intrusions (mostly granodioritic types, including porphyry copper deposits). We suggest that the Late Eocene-Early Oligocene belt formed when fast and oblique convergence between the South America and Farallon plates led to flat subduction and direct melting of the subducting plate, hence giving rise to plutonic rocks of adakitic affinity. The absence of volcanism, under prevailing compressional conditions, prevented the escape of SO2 from the adakitic, sulfur-rich, highly oxidized magmas ("closed porphyry system"), which allowed formation of huge mineral deposits. On the contrary, coeval volcanic activity during formation of the Paleocene-Early Eocene calc-alkaline porphyries allowed development of "open systems", hence to outgassing, and therefore, to small mineral deposits. 相似文献
145.
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
146.
147.
Ivan K. Baldry Timothy R. Bedding 《Monthly notices of the Royal Astronomical Society》2000,318(2):341-353
We present time-series spectroscopy of the rapidly oscillating Ap (roAp) star HR 3831. This star has a dominant pulsation period of 11.7 min and a rotation period of 2.85 d. We have analysed 1400 intermediate-resolution spectra of the wavelength region 6100–7100 Å obtained over one week, using techniques similar to those we applied to another roAp star, α Cir.
We confirm that the H α velocity amplitude of HR 3831 is modulated with rotation phase. Such a modulation was predicted by the oblique pulsator model, and rules out the spotted pulsator model. However, further analysis of H α and other lines reveals rotational modulations that cannot easily be explained using the oblique pulsator model. In particular, the phase of the pulsation as measured by the width of the H α line varies with height in the line.
The variation of the H α bisector shows a very similar pattern to that observed in α Cir, which we have previously attributed to a radial node in the stellar atmosphere. However, the striking similarities between the two stars, despite the much shorter period of α Cir (6.8 min), argues against this interpretation unless the structure of the atmosphere is somewhat different between the two stars. Alternatively, the bisector variation is a signature of the degree ℓ of the mode and not the overtone value n .
High-resolution studies of the metal lines in roAp stars are needed to understand fully the form of the pulsation in the atmosphere. 相似文献
We confirm that the H α velocity amplitude of HR 3831 is modulated with rotation phase. Such a modulation was predicted by the oblique pulsator model, and rules out the spotted pulsator model. However, further analysis of H α and other lines reveals rotational modulations that cannot easily be explained using the oblique pulsator model. In particular, the phase of the pulsation as measured by the width of the H α line varies with height in the line.
The variation of the H α bisector shows a very similar pattern to that observed in α Cir, which we have previously attributed to a radial node in the stellar atmosphere. However, the striking similarities between the two stars, despite the much shorter period of α Cir (6.8 min), argues against this interpretation unless the structure of the atmosphere is somewhat different between the two stars. Alternatively, the bisector variation is a signature of the degree ℓ of the mode and not the overtone value n .
High-resolution studies of the metal lines in roAp stars are needed to understand fully the form of the pulsation in the atmosphere. 相似文献
148.
Coastal cliff geometry derived from structure-from-motion photogrammetry at Stara Baška,Krk Island,Croatia 总被引:1,自引:1,他引:0
The aim of this study was to examine the capability of structure-from-motion photogrammetry in defining the geometry of cliffs and undercuts in rocks of complex geomorphology. A case site was chosen along pocket beaches near the village of Stara Ba?ka on the Adriatic Sea island of Krk, Gulf of Kvarner, Croatia, where cliff erosion of 5 m in breccias was identified by comparison of aerial photographs from 1960 and 2004. The 3D point cloud was derived from approx. 800 photos taken on 9 January 2014 by a single camera from various elevations and angles, and processed using the online software ReCap (Autodesk). Data acquisition was found to be quick and the method easy to implement. The difference between the georeferenced 3D cloud points and an RTK-GPS survey was 7 cm, i.e. within the limits of RTK-GPS precision. Quantifying the spatial variation in undercut geometries revealed that the deepest and largest (17 m3) undercut was in the south-eastern sector of the beach. Reconstructing the detailed geomorphology of this 3.8-m-deep undercut convincingly demonstrates the high efficiency of the method. Such assessments of spatiotemporal changes in undercut and overhang volumes can prove useful for evaluations of cliff erosion risk. Coupled with the low cost and relatively simple application, this is evidently an attractive technique for meaningful geotechnical and coastal engineering monitoring in the future on the island of Krk and, for that matter, also on other Adriatic islands and in similar settings worldwide. 相似文献
149.
Displacement patterns of a landslide affected by human activities: insights from ground-based InSAR monitoring 总被引:2,自引:0,他引:2
Francesca Bozzano Ivan Cipriani Paolo Mazzanti Alberto Prestininzi 《Natural Hazards》2011,59(3):1377-1396
Landslides interacting with large infrastructures represent a major problem for the economy, society as a whole, and the safety
of workers. Continuous monitoring for 23 months using an integrated platform with a ground-based SAR interferometer (GB-InSAR),
a weather station, and an automatic camera gave us the opportunity to analyze the response of an unstable slope to the different
phases of work. The deformational behavior of both the natural slope and the man-made structures was recorded and interpreted
in relation to the working stages and the rainfall conditions during the whole monitoring period. A typical pattern of displacement
was identified for shallow landslides, debris produced by the excavation and gabions, metallic walls, and anchored bulkheads.
Furthermore, insights into the dynamics and behavior of the slope and the man-made structures that interact with the landslide
were obtained. Extreme rainfall is the main trigger of shallow landslides and gabion deformations, while anchored bulkheads
are less influenced by rainfalls. Movement of debris that is produced by excavations and temporary metallic barrier deformation
are closely related to each other. The herein proposed monitoring platform is very efficient in monitoring unstable slopes
that are affected by human activities. Moreover, the recorded patterns of displacement in the slope and the man-made structures
can be used as reference data for similar studies and engineering designs. 相似文献
150.
Julie SucharováIvan Suchara Clemens Reimann Rognvald BoydPeter Filzmoser Peter Englmaier 《Applied Geochemistry》2011,26(7):1205-1214
Lead concentrations were determined in samples of soil B-horizon (N = 258), forest-floor humus (O-horizon, N = 259), grass (Avenella flexuosa, N = 251) and spruce (Picea abies, N = 253) needles (2nd year) collected at the same locations evenly spread over the territory of the Czech Republic at an average density of 1 site/300 km2. Median Pb concentrations differ widely in the four materials: soil B-horizon: 27 mg/kg (3.3-220 mg/kg), humus: 78 mg/kg (19-1863 mg/kg), grass: 0.37 mg/kg (0.08-8 mg/kg) and spruce needles: 0.23 mg/kg (0.07-3 mg/kg). In the Pb distribution maps for humus, grass and spruce a number of well-known Pb-contamination sources are indicated by unusually high concentrations (e.g., the Pb smelter at Pribram, the metallurgical industry in the NE of the Czech Republic and along the Polish border, as well as the metallurgical industry in Upper Silesia and Europe’s largest coal-fired power plant at Bogatynia, Poland). The ratio 206Pb/207Pb was determined in all four materials. The median value of the 206Pb/207Pb isotope ratio in the soil B-horizon is 1.184 (variation: 1.145-1.337). In both humus and grass the median value for the 206Pb/207Pb isotope ratio is 1.162 (variation: 1.130-1.182), in spruce needles the median ratio is 1.159 (variation: 1.116-1.186). In humus, grass and spruce needles the known contamination sources are all marked by higher 206Pb/207Pb isotope ratios in the maps. Furthermore, the soil B-horizon, humus, grass and spruce needles show distinctly different spatial distribution patterns of the 206Pb/207Pb isotope ratios. The B-horizon does not provide a viable background value for metal concentrations in the O-horizon or plant materials. None of the maps provides evidence for the importance of traffic-related emissions for the observed isotope ratios at the scale of the Czech Republic. 相似文献