Morphology of the ovotestis of Serranus atricauda (Teleostei,Serranidae)     

María Mercedes García-Díaz  María José Lorente  José Antonio González  Víctor Manuel Tuset 《Aquatic Sciences - Research Across Boundaries》2002,64(1):87-96

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Active tectonics of the South Caspian Basin   总被引：15，自引：0，他引：15  

James Jackson  Keith Priestley  Mark Allen  Manuel Berberian 《Geophysical Journal International》2002,148(2):214-245

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Alpujarride attribution of the supposed ‘Almagride Complex’ (Betic Internal Zone,Almerı́a Province,Spain)Appartenance Alpujarride du prétendu « Complexe almagride » (Zones internes bétiques,province d'Almeria,Espagne)     

Carlos Sanz de Galdeano  Francisco J Garcı́a Tortosa 《Comptes Rendus Geoscience》2002,334(5):355-362

The differentiation of units in the Sierra de Almagro has been a source of controversy. There were defined the Almagride and Ballabona–Cucharón complexes, the former considered by several authors as part of a Subbetic metamorphosed and outcropping in a tectonic window. In this study, the units of Ballabona, Almagro and Cucharón are integrated into a single one, that of Tres Pacos, because they correspond to different parts of the same stratigraphic series. This unit is tectonically over the Nevado–Filabride Complex. The existence of the Almagride and Ballabona–Cucharón complexes is discarded and their units form part of the Alpujarride Complex. To cite this article: C. Sanz de Galdeano, F.J. Garc??a Tortosa, C. R. Geoscience 334 (2002) 355–362.  相似文献   

Seasonal variation of the soil seed bank of grasses in central Argentina as related to grazing and shrub cover   总被引：1，自引：0，他引：1  

M. D. Mayor  R. M. Bo  D. V. Pelez  O. R. Elía 《Journal of Arid Environments》2003,53(4):467

The objectives of this research were to (a) study seasonal variation of the seed bank of grasses in two areas with different grazing history, (b) analyse the effect of the presence of shrubs on the seed bank and (c) study seed viability and dormancy in buried seeds of Piptochaetium napostaense and Stipa tenuis. The seed density of grasses was in general low and showed seasonal variation. Most of the grasses showed maximum seed density in December when seed dispersal occurs. Shrub cover did not show a marked influence in seed accumulation. The relatively high number of damaged seeds suggests that predation may be an important factor in seed bank dynamics in the Caldenal. Seeds of dominant perennial forage grasses showed dormancy that could explain, at least in part, persistence of these species in spite of periodical disturbance.  相似文献   

Inelastic displacement ratios for evaluation of existing structures     

Jorge Ruiz‐García  Eduardo Miranda 《地震工程与结构动力学》2003,32(8):1237-1258

Results of a detailed statistical study of constant relative strength inelastic displacement ratios to estimate maximum lateral inelastic displacement demands on existing structures from maximum lateral elastic displacement demands are presented. These ratios were computed for single‐degree‐of‐freedom systems with different levels of lateral strength normalized to the strength required to remain elastic when subjected to a relatively large ensemble of recorded earthquake ground motions. Three groups of soil conditions with shear wave velocities higher than 180m/s are considered. The influence of period of vibration, level of lateral yielding strength, site conditions, earthquake magnitude, distance to the source, and strain‐hardening ratio are evaluated and discussed. Mean inelastic displacement ratios and those associated with various percentiles are presented. A special emphasis is given to the dispersion of these ratios. It is concluded that distance to the source has a negligible influence on constant relative strength inelastic displacement ratios. However, for periods smaller than 1s earthquake magnitude and soil conditions have a moderate influence on these ratios. Strain hardening decreases maximum inelastic displacement at a fairly constant rate depending on the level of relative strength for periods of vibration longer than about 1.0s while it decreases maximum inelastic displacement non‐linearly as the period of vibration shortens and as the relative‐strength ratio increases for periods of vibration shorter than 1.0s. Finally, results from non‐linear regression analyses are presented that provide a simplified expression to be used to approximate mean inelastic displacement ratios during the evaluation of existing structures built on firm sites. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

He and Ne isotopes in oceanic crust: implications for noble gas recycling in the mantle     

Manuel Moreira  Jerzy Blusztajn  Joshua Curtice  Stan Hart  Henry Dick  Mark D. Kurz 《Earth and Planetary Science Letters》2003,216(4):635-643

In an attempt to determine the helium and neon isotopic composition of the lower oceanic crust, we report new noble gas measurements on 11 million year old gabbros from Ocean Drilling Program site 735B in the Indian Ocean. The nine whole rock samples analyzed came from 20 to 500 m depth below the seafloor. Helium contents vary from 3.3×10⁻¹⁰ to 2.5×10⁻⁷ ccSTP/g by crushing and from 5.4×10⁻⁸ to 2.4×10⁻⁷ ccSTP/g by melting. ³He/⁴He ratios vary between 2.2 and 8.6 Ra by crushing and between 2.9 and 8.2 by melting. The highest R/Ra ratios are similar to the mean mid-ocean ridge basalt (MORB) ratio of 8±1. The lower values are attributed to radiogenic helium from in situ α-particle production during uranium and thorium decay. Neon isotopic ratios are similar to atmospheric ratios, reflecting a significant seawater circulation in the upper 500 m of exposed crust at this site. MORB-like neon, with elevated ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios, was found in some high temperature steps of heating experiments, but with very small anomalies compared to air. These first results from the lower oceanic crust indicate that subducted lower oceanic crust has an atmospheric ²⁰Ne/²²Ne ratio. Most of this neon must be removed during the subduction process, if the ocean crust is to be recirculated in the upper mantle, otherwise this atmospheric neon will overwhelm the upper mantle neon budget. Similarly, the high (U+Th)/³He ratio of these crustal gabbros will generate very radiogenic ⁴He/³He ratios on a 100 Ma time scale, so lower oceanic crust cannot be recycled into either MORB or oceanic island basalt without some form of processing.  相似文献   

Cenozoic Plate interaction of the Australia and Philippine Sea Plates: “hit-and-run” tectonics     

Manuel Pubellier  Jason Ali  Christophe Monnier 《Tectonophysics》2003,363(3-4):181-199

Recent studies in northwest New Guinea have shown the presence of at least two marginal basins of different age, both of which formed in back-arc settings. The older basin opened between the Middle Jurassic and Early Cretaceous, a remnant of which is now preserved as the New Guinea Ophiolite. Its obduction started at 40 Ma and it was finally emplaced on the Australian margin at 30 Ma. The younger basin was active during the Oligocene to Middle Miocene and was obducted in the Early Pliocene. Studies of the western edge of the Philippine Sea also reveal an important deformation of the Philippine arc in the Oligocene, which hitherto has remained unexplained. Using information from these systems, paleomagnetic results, kinematic reconstructions and geochemistry of the supra-subduction ophiolite, we present a plate model to explain the region's Eo–Oligocene development. We suggest that an extensive portion of oceanic crust extended the Australian Plate a considerable distance north of the Australian Craton. As Australia began its steady 7–8 cm/year northward drift in the Early Eocene, this lithosphere was subducted. Thus, the portion of the Philippine Sea Plate carrying the Taiwan–Philippine Arc to its present site may have actually been in contact with the ophiolite now in New Guinea and obduction led to deformation of the Philippine Sea Plate itself. Neogene Plate kinematics transported the deformed belt in contact with the Sunda block in the Late Miocene and Pliocene. This interpretation has implications for the origin for the Philippine Sea Plate and the potential incorporation of continental fragments against its boundaries.  相似文献   

The Influence of Geomorphologic Heritage on Present Nival Erosion: Peñalara, Spain     

David Palacios  & Manuel García Sánchez-Colomer 《Geografiska Annaler: Series A, Physical Geography》1997,79(1-2):25-40

This article examines how snow plays a role in current erosive processes in a high mountain area (1800—2400 m a.s.l.) known as Peñalara, located in Spain's Central Range (40°50' N; 3°58' W). The hypothesis maintains that snow becomes an important erosive factor when it accumulates over sedimentary or weathered materials, therefore geomorphological heritage is a key factor in nival erosion. To test this hypothesis, the authors identified the landforms in the study area and determined their relative ages by weathering and lichenometry ( Rizocarpon geographicum ag. ), differentiating between preglacial, glacial (Recent Pleistocene) and postglacial (Holocene) forms. The information was used to plot a reticulate pattern of observation sites for the study area. Snow depth and the movement of selected blocks at each site were recorded from October 1991 to June 1995. The relationship between late-lying snowpatches, geomorphological heritage and current erosive processes was determined. Between 1800 and 2000 m a.s.l., there is an indirect relationship between snowpatches and predominant processes (stream incision and gelifluction) on terminal moraines. Between 2000 and 2200 m, direct action is present where there are late-laying snowpatches on lateral moraines and some glacial steps. Between 2200 and 2400 m, gelifraction and gravity processes are also in direct relation to snowpatches.  相似文献   

Foliation fields and 3D cartography in geology: Principles of a method based on potential interpolation   总被引：4，自引：0，他引：4  

Christian Lajaunie  Gabriel Courrioux  Laurent Manuel 《Mathematical Geology》1997,29(4):571-584

A modeling method that takes into account known points on a geological interface and plane orientation data such as stratification or foliation planes is described and tested. The orientations data do not necessarily belong to one of the interfaces but are assumed to sample the main anisotropy of a geological formation as in current geological situations. The problem is to determine the surfaces which pass through the known points on interfaces and which are compatible with the orientation data. The method is based on the interpolation of a scalar field defined in the space the gradient in which is orthogonal to the orientations, given that some points have the same but unknown scalar value (points of the same interface), and that scalar gradient is known on the other points (foliations). The modeled interfaces are represented as isovalues of the interpolated field. Preliminary two-dimensional tests carried-out with different covariance models demonstrate the validity of the method, which is easily transposable in three dimensions.  相似文献   

Converting Radial Distortions Due to Geopotential Models to Geopotential Stokes Coefficients     

Burša  Milan 《Studia Geophysica et Geodaetica》1997,41(4):407-415

A methodology for improving geopotential models has been developed. Theoretical relations have been derived converting coefficients in harmonic expansions for radial distortions due to geopotential models into geopotential Stokes coefficients. Terms of the order of 10 ^–10 in magnitude have been retained.  相似文献