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排序方式: 共有433条查询结果,搜索用时 31 毫秒
271.
Claudio Zanolla Carla Braitenberg Jrg Ebbing Marcello Bernabini Kurt Bram Gerald Gabriel Hans-Jürgen Gtze Salvatore Giammetti Bruno Meurers Rinaldo Nicolich Franco Palmieri 《Tectonophysics》2006,414(1-4):127
The deep seismic profile Transalp crosses, from north to south, Germany, Austria and Italy. The gravity measurements for each country were made by national agencies with different reference systems and data reduction methods. Within the frame of the Transalp-project a comprehensive database of the Eastern Alps was compiled covering an area of 3.5° by 4° in longitude and latitude (275 by 445 km), respectively. To increase the data coverage in the south Alpine area two gravity surveys were carried out, resulting in 469 areally distributed new stations, of which 215 have been measured with the intent to improve the geoid in the area of the planned Brenner Basistunnel (BBT). The resulting gravity database is the best in terms of resolution and data quality presently available for the Eastern Alps. Here the free air, Bouguer and isostatic gravity fields are critically discussed. The spatial density of existing gravity stations in the three countries is discussed. On the Italian side of the Alps the spatial density is rather sparse compared to the Austrian side. The Bouguer-gravity field varies between − 190 * 10− 5 m/s2 and + 25 * 10− 5 m/s2, with the minimum located along the Alpine high topographic chain, but with a small offset (a few tens of km) to the greatest topographic elevation, showing that the Airy-type local isostatic equilibrium does not fully apply here. The maximum of the Bouguer anomaly has an elongated shape of 100 by 50 km located between the towns of Verona and Vicenza and covers the Venetian Tertiary Volcanic Province (VTVP), a feature not directly related to the plate collision in the Eastern Alps. The gravity high is only partly explainable by high-density magmatic rocks and requires also a deeper source, like a shallowing of the Moho. The isostatic residual anomalies (Airy model) are in the range ± 50 * 10− 5 m/s2, with the greatest positive anomaly corresponding to the location of the VTVP, indicating here under-compensation of masses. At last a discussion of a 2D density model based on reflection seismic data and receiver functions is made. 相似文献
272.
273.
Migration and accumulation of ultra-depleted subduction-related melts in the Massif du Sud ophiolite (New Caledonia) 总被引:1,自引:0,他引:1
Claudio Marchesi Carlos J. Garrido Marguerite Godard France Belley Eric Ferr 《Chemical Geology》2009,266(3-4):180-195
The Massif du Sud is a large ophiolitic complex that crops out in the southern region of New Caledonia (SW Pacific). It is dominated by harzburgite tectonite that locally shows a transitional gradation to massive dunite up section. Clinopyroxene, orthopyroxene and plagioclase progressively appear in dunite up to the transition to layered wehrlite and orthopyroxene–gabbro. The dunite–wehrlite and wehrlite–gabbro contacts are parallel and the latter defines the paleo-Moho.Highly depleted modal, mineral and bulk rock compositions indicate that harzburgites are residues after high degrees (20–30%) of partial melting mainly in the spinel-stability field. Their relative enrichment in HFSE, LREE and MREE is due to re-equilibration of melting residues with percolating melts. Dunite formed in the Moho transition zone by reaction between residual mantle harzburgite and olivine-saturated melts that led to pyroxene dissolution and olivine precipitation. Rare clinopyroxene and plagioclase crystallized in interstitial melt pores of dunite from primitive, low-TiO2, ultra-depleted liquids with a geochemical signature transitional between those of island arc tholeiites and boninites.Ascending batches of relatively high-SiO2, ultra-depleted melts migrated through the Moho transition zone and generated wehrlite by olivine dissolution and crystallization of clinopyroxene, orthopyroxene and plagioclase in variable amounts. These liquids were more evolved and were produced by higher degrees of melting or from a more depleted source compared with melts that locally crystallized clinopyroxene in dunite. Ultra-depleted magmas, non-cogenetic with those that formed the Moho transition zone, ascended to the lower crust and generated gabbroic cumulates with subduction-related affinity. Thus, the ultramafic and mafic rocks in the Moho transition zone and lower crust of the Massif du Sud ophiolite are not products of fractional crystallization from a single magma-type but are the result of migration and accumulation of different melts in a multi-stage evolution.The record of high partial melting in the mantle section, and migration and accumulation of ultra-depleted subduction-related melts in the Moho transition zone and lower crust support that the Massif du Sud ophiolite is a portion of forearc lithosphere generated in an extensional regime during the early phases of the subduction zone evolution. Our results show the existence of different types of ultra-depleted melt compositions arriving at the Moho transition zone and lower crust of an infant intraoceanic paleo-arc. Ultra-depleted melts may thus be a significant component of the melt budget generated in oceanic spreading forearcs prior to aggregation and mixing of a large range of melt compositions in the crust. 相似文献
274.
A hypoplastic macroelement model for shallow foundations under monotonic and cyclic loads 总被引:3,自引:3,他引:0
In this work, a macroelement for shallow foundations on sands has been developed based on the theory of hypoplasticity. The
incrementally nonlinear constitutive equations of the macromodel are defined in terms of generalized forces and displacements
and are constructed based on the general approach proposed by Niemunis (Extended Hypoplastic Models for Soils. Habilitation
Thesis, Bochum University, 2002). A suitable vectorial internal variable—mimicking the concept of intergranular strain introduced
by Niemunis and Herle (Mech Cohes Frict Mater 2:279–299, 1997) for continuum hypoplasticity—is employed to provide the model
sufficient memory of past displacement history to be able to reproduce the observed behavior under cyclic loading paths. As
compared to similar macroelements formulated within the framework of the theory of elastoplasticity, the proposed approach
has the advantage of a much simpler mathematical structure, which allows a straightforward implementation in existing structural
analysis FE codes. The model performance has then been evaluated by comparing the model predictions with available experimental
results from a series of small-scale model tests reported by Nova and Montrasio (Géotechnique 41:243–256, 1991). Overall,
the model captures reasonably well the observed response under nonproportional, complex loading paths. A series of simulations
reproducing the tests performed by di Prisco et al. (Shallow footing under cyclic loading: experimental behaviour and constitutive
modelling. Patron, Bologna, 2003) has also demonstrated the potential of the proposed model to simulate the observed behavior
of footings under cyclic loading paths, at least from a qualitative point of view. 相似文献
275.
Alejandro Dussaillant Wouter Buytaert Paul Carling Claudio Meier Fabián Espinoza 《Natural Hazards》2010,54(2):469-481
Five similar glacial-lake outburst floods (GLOFs) occurred in April, October, December 2008, March and September 2009 in the Northern Patagonia Icefield. On each occasion, Cachet 2 Lake, dammed by the Colonia Glacier, released circa 200-million m3 water into the Colonia River. Refilling has occurred rapidly, such that further outbreak floods can be expected. Pipeflow calculations of the subglacial tunnel drainage and 1D hydraulic models of the river flood give consistent results, with an estimated peak discharge surpassing 3,000 m3 s?1. These floods were larger in magnitude than any flood on record, according to gauged data since 1963. However, geomorphological analysis of the Colonia valley shows physical evidence of former catastrophic outburst floods from a larger glacial-lake, with flood discharges possibly as high as 16,000 m3 s?1. Due to potential impacts of climate change on glacier dynamics in the area, jökulhlaups may increase future flood risks for infrastructure and population. This is particularly relevant in view of the current development of hydropower projects in Chilean Patagonia. 相似文献
276.
Claudio Faccenna Michele Soligo Andrea Billi Luigi De Filippis Renato Funiciello Claudio Rossetti Paola Tuccimei 《Global and Planetary Change》2008,63(4):299-308
The depositional and erosional history of the Lapis Tiburtinus endogenic travertine located circa 25 km to the east of Rome, Central Italy, near the Colli Albani quiescent volcano, is interpreted through three-dimensional stratigraphy and uranium-series geochronology. Analyses of large exposures located in active quarries and of cores obtained from 114 industrial wells reveal that the travertine deposit is about 20 km2 wide and 60 m thick on average. The travertine thickness is over 85 m toward its western N–S-elongated side, where thermal springs and large sinkholes occur aligned over a seismically-active N-striking fault. The travertine age was calculated using the U/Th isochron method. Results constrain the onset and conclusion of travertine deposition at about 115 and 30 ka, respectively. The three-dimensional study of the travertine shows that this deposit is characterized by a succession of depositional benches grown in an aggradational fashion. The benches are separated by five main erosional surfaces, which are associated with paleosols, conglomerates, and karstic features. This evidence shows that the travertine evolution was mostly controlled by water table fluctuations. Chronological correlations between travertine evolution and paleoclimate indicators suggest that the travertine deposition was partly modulated by climate conditions. Other influencing factors may have been fault-related deformation and volcanic events. 相似文献
277.
278.
Height bias and scale effect induced by antenna gravitational deformations in geodetic VLBI data analysis 总被引:2,自引:2,他引:0
The impact of signal path variations (SPVs) caused by antenna gravitational deformations on geodetic very long baseline interferometry
(VLBI) results is evaluated for the first time. Elevation-dependent models of SPV for Medicina and Noto (Italy) telescopes
were derived from a combination of terrestrial surveying methods to account for gravitational deformations. After applying
these models in geodetic VLBI data analysis, estimates of the antenna reference point positions are shifted upward by 8.9
and 6.7 mm, respectively. The impact on other parameters is negligible. To simulate the impact of antenna gravitational deformations
on the entire VLBI network, lacking measurements for other telescopes, we rescaled the SPV models of Medicina and Noto for
other antennas according to their size. The effects of the simulations are changes in VLBI heights in the range [−3, 73] mm
and a net scale increase of 0.3–0.8 ppb. The height bias is larger than random errors of VLBI position estimates, implying
the possibility of significant scale distortions related to antenna gravitational deformations. This demonstrates the need
to precisely measure gravitational deformations of other VLBI telescopes, to derive their precise SPV models and to apply
them in routine geodetic data analysis. 相似文献
279.
Simulation study of the influence of the ionospheric layer height in the thin layer ionospheric model 总被引:2,自引:1,他引:1
This work aims to contribute to the understanding of the influence of the ionospheric layer height (ILH) on the thin layer
ionospheric model (TLIM) used to retrieve ionospheric information from the GNSS observations. Particular attention is paid
to the errors caused on the estimation of the vertical total electron content (vTEC) and the GNSS satellites and receivers inter-frequency biases (IFB), by the use of an inappropriate ILH. The work relies
upon numerical simulations performed with an empirical model of the Earth’s ionosphere: the model is used to create realistic
but controlled ionospheric scenarios and the errors are evaluated after recovering those scenarios with the TLIM. The error
assessment is performed in the Central and the northern part of the South American continents, a region where large errors
are expected due to the combined actions of the Appleton Anomaly of the ionosphere and the South-Atlantic anomaly of the geomagnetic
field. According to this study, there does not exist a unique ILH that cancels the vTEC error for the whole region under consideration. The ILH that cancels the regional mean vTEC error varies with the solar activity and season. The latitude-dependent conversion error propagates to the parameters of
the model used to represent the latitudinal variation on the vTEC on the ionospheric layer, and to the IFB, when these values are simultaneously estimated from the observed sTEC. Besides, the ILH that cancels the regional mean vTEC error is different from the one that cancels the IFB error and the difference between both ILH varies with the solar activity
and season. 相似文献
280.
Ying Zhang Claudio Cassardo Chengzhi Ye Marco Galli Naima Vela 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(1):63-77
Landfall tropical cyclones are a major kind of severe weather affecting China. The typhoon Sepat, declassified as tropical storm after its landfalling, caused a continuous heavy rainfall event over China mainland from 19th to 25th August, 2007. The storm cyclone resided over the Hunan province for 60 hours, causing observed accumulated precipitation larger than 300 mm in a large area of the Hunan province and leading severe flood events. This event was simulated using the Weather Research and Forecasting (WRF) model coupled with the surface layer scheme UTOPIA. The model was able to reproduce the main characteristics of the event, including the typhoon track and the rainfall field and timing. In addition, three sets of sensitivity experiments have been performed. In the first one, the effects of different land surface schemes (RUC, NOAH and UTOPIA) coupled with WRF on the precipitation, sensible and latent heat flux fields associated with the Typhoon Sepat (2007) were investigated. The second set of sensitivity experiments analyzed the role of the surface fluxes (sensible and latent heat flux) on the typhoon evolution. The third set of sensitivity experiments regarded the initialization of the soil moisture content. These experiments showed that both latent and sensible heat fluxes sustained this landfalling typhoon, maintaining the spiral structure of rain belt. Among the two fluxes, the latent heat one played a major role in determining the intensity, the track and the rainfall distribution of the typhoon. In addition, the correct initialization of the soil moisture content has reveled a fundamental parameter to be initialized in order to correctly evaluate the distribution and intensity of the rain field. The intercomparison between the three different land surface schemes coupled with WRF showed that the WRF-UTOPIA and WRF-NOAH outputs seem comparable between each other and physically most realistic than those of WRF-RUC. These analyses were helpful to understand the evolution and the development of the landfalling typhoon, and demonstrated that WRF-UTOPIA and WRF-NOAH could be considered a good tool for managing the risk evaluation connected with the occurrence of such events at regional scale. 相似文献