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Antonis Polatidis Anastasia Kiratzi Panagiotis Hatzidimitriou Basil Margaris 《Tectonophysics》2003,367(1-2):29-40
Qβ for shear-waves is determined for the inner part of the Hellenic arc, the back-arc area, as a function of frequency in the range 0.6–16 Hz. We used 314 digital records from 32 earthquakes with magnitudes (Mw) ranging from 3.9 to 5.1. Epicentral distances ranged from 65 to 515 km. The data were obtained in 1997 during a 6-month operation of a digital portable network in Greece. The Qβ estimates were made for five frequency bands centred at 0.8, 1.5, 3.0, 6.0 and 12.0 Hz and the Qβ values obtained were 47, 79, 143, 271 and 553, respectively. The results show that Qβ for S-waves increases with frequency taking the form Qβ=55f 0.91 (or Qβ−10.018f−0.91). The high attenuation and the strong frequency dependence found, which is close to the frequency dependence of coda Q for Greece, are characteristic of an area with high seismicity, rapid extension, and in agreement with other similar studies in Greece. 相似文献
3.
Preface: Proceedings of the 5th International Symposium on Lithographic Limestone and Plattenkalk 总被引:1,自引:0,他引:1
Daniel Marty Jean-Paul Billon-Bruyat Christian A. Meyer Loïc Costeur Basil Thüring 《Swiss Journal of Geoscience》2011,104(1):1-29
Magmatic rocks from the pre-Mesozoic basements of the Sambuco and Maggia nappes have been dated by U–Pb zircon ages with the LA-ICPMS technique. Several magmatic events have been identified in the Sambuco nappe. The mafic banded calc-alkaline suite of Scheggia is dated at 540 Ma, an age comparable to that of mafic rocks in the Austroalpine Silvretta nappe. The Sasso Nero peraluminous augengneiss has an age of 480–470 Ma, like many other “older orthogneisses” in Alpine basement units. It hosts a large proportion of inherited zircons, which were dated around 630 Ma, a Panafrican age indicating the Gondwanan affiliation of the Sambuco basement. The calc-alkaline Matorello pluton yielded ages around 300 Ma, similar to numerous Late Carboniferous intrusions in other basement units of the Lower Penninic (Monte Leone, Antigorio, Verampio) and Helvetic domains (Gotthard and other External Crystalline Massifs). Associated lamprophyric dykes are slightly younger (300–290 Ma), like similar dykes sampled in gneiss blocks included in the sedimentary cover of the underlying Antigorio nappe (290–285 Ma). The Cocco granodiorite and Rüscada leucogranite, both intruding the basement of the neighbouring Maggia nappe, yielded ages of ca. 300–310 Ma, identical within errors to the age of the Matorello pluton. They are significantly older than former age determinations. This age coincidence, coupled with remarkable petrologic similarities between the Cocco and Matorello granodiorites, strongly suggests paleogeographic proximity of the Sambuco and Maggia nappes in Late Carboniferous times. In recent publications these two nappes have been interpreted as belonging to distinct Mesozoic paleogeographic domains: “European” for Sambuco and “Briançonnais” for Maggia, separated by the “Valais” oceanic basin. In this case, the similarity of the Matorello and Cocco intrusions would demonstrate the absence of any significant transcurrent movement between these two continental domains. Alternatively, according to a more traditional view, Sambuco and Maggia might belong to a single large Alpine tectonic unit. 相似文献
4.
Multi‐channel Advanced Very‐High Resolution Radiometer (AVHRR) images of sea surface temperature (SST) in the New Zealand region have been archived since 1989. A comparison of these data with conductivity‐temperature‐depth (CTD) and expendable bathythermograph (XBT) data shows that the AVHRR temperatures are about 7% too high (when expressed in °C). Once the AVHRR temperatures have been corrected, they measure SST with an uncertainty of about 0.7°C. 相似文献
5.
The restoring capability (or re‐centering capability) is identified by the current design codes as a fundamental feature of seismic isolation systems. In this paper, the restoring capability of bilinear hysteretic or frictional seismic isolation systems is investigated in some detail. Certain energy considerations are examined first in order to provide insight into and reveal governing parameters on individual aspects of the problem. The restoring capability is then investigated through an extensive parametric study of smooth bilinear single‐degree‐of‐freedom hysteretic systems, with parameters covering a range of typical seismic isolation systems, subjected to a large group of recorded earthquakes. The results of the parametric analyses are processed statistically and regression analysis relations are derived that show the dependence of the residual displacement after the earthquake and the cumulative build up of displacements after a series of successive earthquakes on the governing parameters. Based on the analysis results, the features of the bilinear system that ensure sufficient restoring capability are identified. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
6.
Temporal variations in bedload transport rates that occur at a variety of timescales, even under steady flow conditions, are accepted as an inherent component of the bedload transport process. Rarely, however, has the cause of such variations been explained clearly. We consider three data sets, obtained from laboratory experiments, that refer to measurements of bedload transport made with continuously recording bedload traps. Each data set is characterized by a predominant low-frequency oscillation, on which additional higher-frequency oscillations generally are superimposed. The period of these oscillations, as isolated through the use of spectral analysts, ranged between 0·47 and 168 minutes, and was associated unequivocally with the migration of bedforms such as ripples, dunes, and bars. The extent to which such oscillatory behaviour may be recognized in a data set depends on the duration of sampling and the length of the sampling time, with respect to the period of a given bedform. Several theoretical probability distribution functions have been developed to describe the frequency distributions of (relative) bedload transport rates that are associated with the migration of bedforms (Einstein, 1937b; Hamamori, 1962; Carey and Hubbell, 1986). These distribution functions were derived without reference to a sampling interval. We present a modification of Hamamori's (1962) probability distribution function, generated by Monte Carlo simulation, which permits one to specify the sampling interval, in relation to the length of a bedform. Comparisons between the simulated and observed frequency distributions, that were undertaken on the basis of the data described herein, are good (significant at the 90 per cent confidence level). Finally, the implications that temporal variability, which is associated with the migration of bedforms, have for the accurate determination of bedload transport rates are considered. 相似文献
7.
Basil Tikoff Matthew R. Davis Christian Teyssier Michel de St. Blanquat Guillaume Habert Sven Morgan 《Tectonophysics》2005,400(1-4):209-226
The Cascade Lake shear zone occurs on the eastern margin of the Tuolumne Intrusive Suite, Sierra Nevada Batholith, California. Foliation in the zone is NNW trending and subvertical, and lineation is moderately south plunging. Deformation is syn-tectonic with emplacement of the Cathedral Peak granodiorite. A deformation gradient exists toward the NE margin of this pluton, with higher strains and lower temperatures of deformation found near the contact. We compare fabric data collected very densely in this shear zone using several techniques: field fabrics, 3D orientation of K-feldspar megacrysts, and AMS (anisotropy of magnetic susceptibility) analysis. In general, the results from the three different methods are in agreement. Deformation in this shear zone is part of a larger pattern of deformation within the Cathedral Peak granodiorite, as recorded by AMS analysis, and dextral shearing associated within the last stage of plutonism within the Sierra Nevada magmatic arc. 相似文献
8.
A stability model of drainage basin mass balance is used to interpret historic and prehistoric patterns of sediment production, storage and output from the Waipaoa River basin, New Zealand and assess the sensitivity of basin sediment yield to land use change in the historic period. Climate and vegetation cover changed during the late Holocene, but the drainage basin mass balance system was stable before the basin was deforested by European colonists in the late 19th and early 20th centuries. In this meso‐scale dispersal system sediment sources and sinks are closely linked, and before that time there was also little variability in the rate of terrigenous mass accumulation on the adjacent continental shelf. However, despite strong first‐order geologic controls on erosion and extensive alluvial storage, sediment delivery to the continental shelf is sensitive and highly responsive to historic hillslope destabilization driven by land use change. Alluvial buffering can mask the effects of variations in sediment production within a basin on sediment yield at the outlet, but this is most likely to occur in basins where alluvial storage is large relative to yield and where the residence time of alluvial sediment is long relative to the time scale of environmental change. At present, neither situation applies to the Waipaoa River basin. Thus, the strength of the contemporary depositional signal may not only be due to the intensity of the erosion processes involved, but also to the fact that land use change in the historic period destabilized the drainage basin mass balance system. 相似文献
9.
In a basin developed on a stream table, effluent subsurface flow supported a channel network that evolved by a combination of headward growth, lateral widening and divide decay. The area occupied by the developing network increased with time. Circularity was used to characterize network evolution which occurred in three phases (initiation, extension and abstraction). Basin sediment discharge declined exponentially with time. Pronounced quasi-cyclic variability was superimposed upon this general trend. Some of the variability was directly linked to changes in the amount of sediment supplied to the channel. The variation of mean network sediment yield (mean sediment discharge scaled by network area) with time adequately described the general decline in sediment discharge as the network evolved. 相似文献
10.
Basil P. Tritakis 《Astrophysics and Space Science》1983,93(1):141-147
Correlation studies between various solar activity indices and a long time series of annual sums of the maximum value of solar
magnetic field intensity, observed for each group of sunspots during each passage of it over the visible solar hemisphere,
have pointed out a couple of interesting points. First, the faculae have a significant contribution to the numerical representation
of the small scale solar magnetic coefficients and low standard errors of estimation to the above mentioned maximum values
of the solar magnetic field. These properties give to the area index an important physical meaning which is a first approximation
to the small scale solar magnetic fields expressed by the above-mentioned maximum values of it. Finally, the main point which
comes out is that long term studies of the solar magnetic fields, especially extrapolated studies to the past, could be supported
by photospheric indices of the solar activity.
This paper constitutes the expanded version of a report presented to theIAU Symposium No. 102 ‘Solar and Stellar magnetic fields: Origins and coronal effects’, held in Zürich 2–6 August, 1982. 相似文献