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61.
Mauricio da Rocha Fragoso Gabriel Vieira de Carvalho Felipe Lobo Mendes Soares Daiane Gracieli Faller Luiz Paulo de Freitas Assad Raquel Toste Lívia Maria Barbosa Sancho Elisa Nóbrega Passos Carina Stefoni Böck Bruna Reis Luiz Landau Hernan G. Arango Andrew M. Moore 《Ocean Dynamics》2016,66(3):419-434
62.
A redatuming operation is used to simulate the acquisition of data in new levels, avoiding distortions produced by near-surface irregularities related to either geometric or material property heterogeneities. In this work, the application of the true-amplitude Kirchhoff redatuming (TAKR) operator on homogeneous media is compared with conventional Kirchhoff redatuming (KR) operator restricted to the zero-offset case. The TAKR and the KR operators are analytically and numerically compared in order to verify their impacts on the data at a new level. Analyses of amplitude and velocity sensitivity of the TAKR and KR were performed: one concerning the difference between the weight functions and the other related to the velocity variation. The comparisons between operators were performed using numerical examples. The feasibility of the KR and TAKR operators was demonstrated not only kinematically but also dynamically for their purposes. In other words, one preserves amplitude (KR), and the other corrects the amplitude (TAKR). In the end, we applied the operators to a GPR data set. 相似文献
63.
Hrishikesh Samant Ashwin Pundalik Joseph D’souza Hetu Sheth Keegan Carmo Lobo Kyle D’souza Vanit Patel 《Journal of Earth System Science》2017,126(1):9
The Panvel flexure is a 150-km long tectonic structure, comprising prominently seaward-dipping Deccan flood basalts, on the western Indian rifted margin. Given the active tectonic faulting beneath the Panvel flexure zone inferred from microseismicity, better structural understanding of the region is needed. The geology of Elephanta Island in the Mumbai harbour, famous for the ca. mid-6th century A.D. Hindu rock-cut caves in Deccan basalt (a UNESCO World Heritage site) is poorly known. We describe a previously unreported but well-exposed fault zone on Elephanta Island, consisting of two large faults dipping steeply east–southeast and producing easterly downthrows. Well-developed slickensides and structural measurements indicate oblique slip on both faults. The Elephanta Island fault zone may be the northern extension of the Alibag–Uran fault zone previously described. This and two other known regional faults (Nhava–Sheva and Belpada faults) indicate a progressively eastward step-faulted structure of the Panvel flexure, with the important result that the individual movements were not simply downdip but also oblique-slip and locally even rotational (as at Uran). An interesting problem is the normal faulting, block tectonics and rifting of this region of the crust for which seismological data indicate a normal thickness (up to 41.3 km). A model of asymmetric rifting by simple shear may explain this observation and the consistently landward dips of the rifted margin faults. 相似文献
64.
65.
Maria do Carmo P. Gastal Jean Michel Lafon Lo Afraneo Hartmann Edinei Koester 《Journal of South American Earth Sciences》2005,18(3-4):255-276
Combined analyses of Nd isotopes from a wide range of Neoarchaean–Cretaceous igneous rocks provides a proxy to study magmatic processes and the evolution of the lithosphere. The main igneous associations include the Neoproterozoic granitoids from the southern Brazilian shield, which were formed during two tectonothermal events of the Brasiliano cycle: the São Gabriel accretionary orogeny (900–700 Ma) and the Dom Feliciano collisional orogeny (660–550 Ma). Rocks related to the formation of the São Gabriel arc (900–700 Ma) mainly have a depleted juvenile signature. For the Neoproterozoic collisional event, the petrogenetic discussion focuses on two old crustal segments and three types of mantle components. However, no depleted juvenile material was involved in the formation of the Dom Feliciano collisional belt (800–550 Ma), which implies an ensialic environment for the Dom Feliciano orogeny. In the western Neoproterozoic foreland, records of a Neoarchaean lower crust predominate, whereas a Paleoproterozoic crust does in the eastern Dom Feliciano belt. The western foreland includes two amalgamated geotectonic domains, the São Gabriel arc and Taquarembó block. In the collisional belt, the old crust was intensely reworked during the São Gabriel event. In addition to the Neoproterozoic subduction-processed subcontinental lithosphere (São Gariel arc), we recognize two old enriched mantle components, which also are identified in the Paleoproterozoic intraplate tholeiites from Uruguay and the Cretaceous potassic suites from eastern Paraguay. One end member displays the prominent influence of Trans-Amazonian (2.3–2.0 Ga) or older subduction events, whereas the other can be interpreted as a reenrichment of the first during the latest Trans-Amazonian collisional or younger events. This reenriched mantle is documented in late Neoproterozoic suites from the western foreland (605–550 Ma) and younger suites from the eastern collisional belt (600–580 Ma). The other enriched mantle component with an old subduction signature, however, appears only in older rocks of the collisional belt (800–600 Ma). The participation of the subduction-related Brasiliano mantle as an end member of binary mixing occurred in some early Neoproterozoic suites (605–580 Ma) from the western foreland, but the contribution of the Neoarchaean lower crust increased near the late igneous event (575–550 Ma). 相似文献
66.
67.
O. R. Sánchez-Ccoyllo P. L. Silva Dias M. de Fátima Andrade S. R. Freitas 《Meteorology and Atmospheric Physics》2006,92(1-2):83-93
Summary This study is aimed to qualitatively analyze the impact of remote sources on air pollution in the Metropolitan Area of S?o
Paulo (MASP). Air-mass back trajectories from June to August of 1999 were calculated using a three-dimensional kinematic trajectory
model and grouped into trajectory clusters. Correlations of individual trajectory clusters with O3, CO and PM10 concentrations were determined. In this model, trajectories were obtained using the means of the three wind velocity components
(U, V and W). The three-dimensional wind field was derived from the Regional Atmospheric Modeling System, and downscaling
was employed. Coarse and fine nested grids (64-km and 16-km horizontal resolution, respectively) were used. Every 12 h (at
00 and 12 UTC), a back-trajectory ensemble, using the 64-km grid, was calculated for five defined endpoints at intervals of
0.5° N, S, E and W of the MASP (λ = 23° 33′S, ϕ = 46° 45′W), that last endpoint being centered in the MASP. To analyze cluster
trajectories, the five trajectory ensembles from each day were allocated into one of four clusters (northeast, southeast,
southwest or northwest quadrant) based on the origin of the trajectory over 4 days. Days on which all five trajectories originated
from the same quadrant were classified as “core” days. Core day concentrations of CO, O3 and PM10 during the study period were evaluated. The results show that, during the study period, air-mass back trajectories in the
MASP originated from all four quadrants: northeast (32%), southeast (12%), southwest (19%) and northwest (37%). Our analysis
of back-trajectory clusters in the MASP suggests a transport to ambient air of O3 precursors and O3 from the northeast region, which is associated with agricultural activities involving biomass burning. 相似文献
68.
Pedro S. Freitas Leon J. Clarke Christopher A. Richardson 《Geochimica et cosmochimica acta》2006,70(20):5119-5133
The relationship between potential elemental proxies (Mg/Ca, Sr/Ca and Mn/Ca ratios) and environmental factors was investigated for the bivalve Pecten maximus in a detailed field study undertaken in the Menai Strait, Wales, U.K. An age model constructed for each shell by comparison of measured and predicted oxygen-isotope ratios allowed comparison on a calendar time scale of shell elemental data with environmental variables, as well as estimation of shell growth rates. The seasonal variation of shell Mn/Ca ratios followed a similar pattern to one previously described for dissolved Mn2+ in the Menai Strait, although further calibration work is needed to validate such a relationship. Shell Sr/Ca ratios unexpectedly were found to co-vary most significantly with calcification temperature, whilst shell Mg/Ca ratios were the next most significant control. The temporal variation in the factors that control shell Sr/Ca ratios strongly suggest the former observation most likely to be the result of a secondary influence on shell Sr/Ca ratios by kinetic effects, the latter driven by seasonal variation in shell growth rate that is in turn influenced in part by seawater temperature. P. maximus shell Mg/Ca ratio to calcification temperature relationships exhibit an inverse correlation during autumn to early spring (October to March-April) and a positive correlation from late spring through summer (May-June to September). No clear explanation is evident for the former trend, but the similarity of the records from the three shells analysed indicate that it is a real signal and not a spurious observation. These observations confirm that application of the Mg/Ca proxy in P. maximus shells remains problematic, even for seasonal or absolute temperature reconstructions. For the range of calcification temperatures of 5-19 °C, our shell Mg/Ca ratios in P. maximus are approximately one-fourth those in inorganic calcite, half those in the bivalve Pinna nobilis, twice those in the bivalve Mytilus trossulus, and four to five times higher than Mg/Ca ratios in planktonic and benthonic foraminifera. Our findings further support observations that Mg/Ca ratios in bivalve shell calcite are an unreliable temperature proxy, as well as substantial taxon- and species-specific variation in Mg incorporation into bivalves and other calcifying organisms, with profound implications for the application of this geochemical proxy to the bivalve fossil record. 相似文献
69.
The authors describe a simple model of an ionization-front propagating in a homogeneous expanding Nova shell. They have estimated the ejected shell mass, the shell ionization time and the Ly-c output from the remnant for several Novae, and present some correlations between these quantities and other Nova parameters. 相似文献
70.
J. A. de Freitas Pacheco 《Astrophysics and Space Science》1975,32(1):205-210
From optical and X-ray data available for the binary X-ray sources, the masses of the components were determined univocally in three systems. A discussion about the masses in other three systems is also presented. Besides Cyg X-1, SMC X-1 is another black-hole candidate. 相似文献