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21.
Pierre-Yves F. Robin 《Geochimica et cosmochimica acta》1979,43(10):1587-1600
Metamorphic segregation is defined here as the formation and growth of bands or domains of different bulk compositions within an originally unbanded rock. It can result from an instability arising in some deforming rocks when diffusion transfer is significant. The nature of this instability is demonstrated separately for a differentiation associated with a crenulation (Type C) and for one without crenulation (Type L). However, the continuous gradation between the two types observed in nature is also expected from the models.A requirement for both types is that one chemical component of the rock, typically silica, diffuse more rapidly than others, e.g. phyllosilicate components, in response to stress-induced pressure gradients. In addition, Type L requires that, at least at an early stage, portions of the rock rich in this mobile component, e.g. rich in quartz, be more competent than those portions which are poor in quartz. By a process akin to the development of pressure shadows, silica diffuses toward domains which are already the richest in quartz. Alternatively, if the rock is chemically open to loss of silica, this silica preferentially originates from dissolution of quartz in the more mica-rich domains. In either case the compositional contrast between domains is increased and metamorphic segregation results. Type C differentiation is best explained if we accept the suggestion made by many petrographers that layer silicates catalyse the pressure-induced transfer of silica. This suggestion can in fact account for other features of metamorphic segregation bands.Metamorphic segregation should also proceed during the development of quartz segregations, quartz rods, slaty cleavage and mylonite banding. The stress distribution argued for Type L bands may also occur in many banded migmatites. In migmatites. however, the assemblage crystallizing in the leucosome may be derived from a circulating hydrothermal fluid as well as from diffusion transfer. 相似文献
22.
Strong motion records of Turkey are studied in order to prepare a catalog to be used as a database for further studies (for instance empirical attenuation laws). The network started to be installed in 1973, and the first record was obtained in 1976. The instruments are of SMA-1 analog recorders and SIG SM-2 and GeoSys GSR-16 digital types. Out of a total of 426 records released on the web sites of the General Directorate of the Disaster Affairs and of Kandili Observatory, a set of 210 records was selected with a satisfactory quality, for which it was possible to associate correctly determined source parameters (source magnitudes and epicentral distances). Most of the records are obtained from around North and East Anatolian Fault zones, as well as from western and southwestern parts of Turkey. The main outcome of this paper is a strong motion catalog of Turkey, with the indication of site conditions, of the frequency band of the reliability of the records, peak values of acceleration, velocity and displacements, source parameters (magnitude, epicentral and macroseismic distances), intensity and finally the fault plane solutions whenever possible. The aim is to have, with other regional dataset, a homogenous and good quality dataset. 相似文献
23.
The shield volcano Erta'Ale, situated in the Danakil Depression, Ethiopia, is known for its active lava lake. In February 2001, our team visited this lake, located inside an 80-m-deep pit, to perform field temperature measurements. The distribution and variation of temperature inside the lake were obtained on the basis of infrared radiation measurements performed from the rim of the pit and from the lake shores. The crust temperature was also determined from the lake shores with a thermocouple to calibrate the pyrometer. We estimated an emissivity of the basalt of 0.74 from this experiment. Through the application of the Stefan-Boltzmann law, we then obtained an estimate of the total radiative heat flux, constrained by pyrometer measurements of the pit, and visual observations of the lake activity. Taking into account the atmospheric convective heat flux, the convected magma mass flux needed to balance the energy budget was subsequently derived and found to represent between 510 and 580 kg s-1. The surface circulation of this mass flux was also analyzed through motion processing techniques applied to video images of the lake. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00445-002-0224-3. 相似文献
24.
Sea level rise (SLR) adversely impacts groundwater quality and capacity of coastal regions. The objectives of this paper are to determine key natural and anthropogenic parameters which may influence and enhance adverse SLR impact upon coastal environments, as well as to assess these natural and anthropogenic components contributing to SLR, and enhance adverse effects of SLR on the environment. This would enable assessment of vulnerability of coastal areas. Components are evaluated in this paper by averaging data relative to respective measured parameters, along with given weightings and assessed ratings, vis-à-vis world maximal reference values. Israel's Mediterranean coast is utilized as an example for such an approach. This can indicate where operational long-term planning measures would be recommended, along with development of effective monitoring and the carrying out of helpful engineering and ecological activities. 相似文献
25.
Ronan Pavic Martin G. Koller Pierre-Yves Bard Corinne Lacave-Lachet 《Journal of Seismology》2000,4(1):59-77
An assessment of uncertainties for ground motion predictions with the aid of the empirical Green's function (EGF) technique is presented. The main input parameters were identified, and their respective uncertainties were assessed by means of an international expert inquiry. The repercussion of these input uncertainties on the final ground motion estimates were investigated by means of the Latin Hypercube Sampling technique. The mean ground motion estimates (response spectra) and their standard deviations were compared with results obtained from empirical attenuation laws. The most sensitive input parameter turned out to be the seismic moment corresponding to the EGF. In general, if the source parameters are well determined, equivalent uncertainties, statistically speaking, can be expected from the EGF technique and from the application of attenuation laws. Therefore, if EGFs with well known source parameters are available, the EGF technique seems to be preferable: site effects are automatically taken into account, and physically realistic acceleration time histories can be obtained. However, further investigations on the reliability of the EGF technique should be performed, and finally, it is recalled that the EGF technique is based on the assumption of linearity. If conditions are such that this assumption cannot be maintained, the EGF technique should be combined with non-linear geotechnical methods. 相似文献
26.
A simple critical-state-based double-yield-surface model for clay behavior under complex loading 总被引:9,自引:4,他引:5
The critical state concept has been widely used in soil mechanics. The purpose of this study is to apply this concept in the framework of multi-mechanism elastoplasticity. The developed model has two yield surfaces: one for shear sliding and one for compression. In this model, the location of the critical state line is explicitly considered and related to the actual material density to control the peak strength and the phase transformation characteristics. The stress reversal technique is incorporated into the model for describing clay behavior under complex loading including changes of stress direction. The determination of the model parameters is discussed; it requires only one drained or undrained triaxial test up to failure with an initial isotropic consolidation stage. The model is used to simulate drained and undrained tests under monotonic loading with different over-consolidation ratios on various remolded and natural clays, including true triaxial tests with different Lode’s angles. Drained and undrained tests under cyclic loadings are also simulated by using the set of parameters determined from monotonic tests. The comparison between experimental results and numerical simulations demonstrate a good predictive ability of this new simple model. 相似文献
27.
Aur��lien Bideaud Benoit Belier Alain Benoit Laurent Berg�� Philippe Camus Sophie Collin Louis Dumoulin Christian Hoffmann Stefanos Marnieros Alessandro Monfardini 《Experimental Astronomy》2011,32(2):179-191
Microbolometers are at present the most sensitive detectors for mm and sub-mm Astronomy. They are in use in most of the present instruments in that bandwidth. We have developed filled arrays of NbSi-based planar antenna coupled microbolometers. The fabrication details are given, together with characterization of the NbSi thermometers and optical results. The optical performances are potentially good for ground-based mm-wave astronomy applications, while the overall detectors performances are limited by low-frequency excess noise in the thermometric NbSi high-impedance sensors (Anderson insulator). 相似文献
28.
Geomorphological study of long-term erosion on a tropical volcanic ocean island: Tahiti-Nui (French Polynesia) 总被引:2,自引:0,他引:2
A quantitative geomorphological study has been made on 27 river basins in Tahiti-Nui volcanic island (French Polynesia) to reconstruct the erosional evolution of a young oceanic island subjected to heavy tropical rainfall. Tahiti-Nui is composed of a main shield volcano cut by two huge landslides on each side of a main E–W rift zone. The northern landslide depression was rapidly buried by the construction of a second shield, the late activity of which overflowed the crest and then filled the southern landslide depression. The island is now volcanically inactive and is deeply dissected by erosion. The present geometries of the river basins are first compared using dimensionless parameters derived from a digital elevation model. The original volcanic surfaces are then reconstructed to estimate the volumes removed by erosion and determine the average rates of long-term erosion. The basins developed on the flanks of the main shield are wider, shallower, and gentler than the basins incising the post-landslide second shield, indicating a higher degree of evolution. Rainfall concentration on the windward (eastern) side of the island also contributed to increase the vertical lowering of the volcanic relief and the enlargement of the valleys. The magnitude of erosion, however, is neither directly linked with the age of the units incised nor with the differential amounts of rainfall. Erosion rates determined over the last 1 Myr range between 10− 3 km3 kyr− 1 and 0.25 km3 kyr− 1. The highest values occur in the basins incising the main E–W rift zone and/or the lateral rims of the northern and southern landslide depressions. Long-term dissection has thus been enhanced along the geological discontinuities of the eruptive system. Deep erosion was first constrained along the axis of the main E–W rift zone, where numerous dykes compartmentalize the volcanic structure into large unstable blocks. Dykes most probably acted as mechanical discontinuities along which shallow gravitational landslides recurrently occurred. Such mass-wasting episodes produced significant amounts of debris, partly preserved as highly indurated sedimentary breccias of various ages exposed at various locations. Subsequent dissection of Tahiti-Nui was enhanced to the north and to the south, leading to the rapid evolution of the Papenoo and Taharuu drainage systems over the last 500 kyr. Long-term dissection on Tahiti-Nui has been responsible for the removal of at least 350 km3 of volcanic material from the surface, and for the partial exhumation of a shallow intrusive complex partly composed of coarse-grained plutonic rocks (gabbros and syenites) in the central part of the eruptive system. Structurally controlled erosion is thus a key component of landscape evolution on such high-relief oceanic tropical islands. 相似文献
29.
Giovanna Cultrera Valerio De Rubeis Nikos Theodoulidis Héloïse Cadet Pierre-Yves Bard 《Bulletin of Earthquake Engineering》2014,12(4):1493-1514
The Horizontal-to-Vertical Spectral Ratio from earthquake (HVSR) and from ambient noise (HVN) recordings realistically indicate the fundamental frequency of soil response but, for the majority of the worldwide examined sites, they do not provide reliable amplification curves as calculated by the earthquake standard Spectral Ratio (SSR). Given the fact that HVSR and especially HVN can be easily obtained, it is challenging to search for a meaningful correlation with SSR amplification functions for the entire frequency band and to use the results for the SSR estimate at a further site where only noise measurements are available. To this aim we used recordings from 75 sites worldwide and we applied a multivariate statistical approach (canonical correlation analysis) to investigate and quantify any correlation among spectral ratios. The canonical correlation between SSR and HVN is then used to estimate the expected SSR at each site by a weighted average of the SSR values measured at the other sites; the weights are properly set to account more for sites with similar behaviour in terms of the canonical correlation results between HVN and SSR. This procedure, repeated for all sites in turn, constitutes the basis of a cross validation. The comparison between the inferred and the original SSR highlights the improvements of site response estimation with respect to the use of ambient noise techniques. The goodness and limitations of the reconstruction procedure are explained by specific geological settings. 相似文献
30.
Acta Geotechnica - This paper studies the dilative behavior of clay during drained creep along triaxial tests under constant mean effective stress, where the volumetric strain is caused by the sole... 相似文献