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1.
Three physical quantities define the essentials of the cosmic ray exposure history of a sample of an iron meteorite: (1) the cosmic ray exposure age T, (2) the pre-atmospheric “size” S of the irradiated body, and (3) the location, i.e. the “depth” D, of the samples within the body. To establish these quantities for a given sample three independent quantities must be determined experimentally. In the present work T is ascertained by the 41K/40K method and the 4He and 21Ne concentrations (C4 and C21) are measured by the isotope dilution method. Signer and Nier's evaluation of the rare gas distribution in the meteorite Grant and the measured exposure age for this meteorite provide the relationships allowing to ascertain for any meteorite the quantities S and D from the 21Ne production rate (P21 = C21/T) and the 4He/21Ne ratio.Earlier measurements have provided data on the isotopic composition of potassium in 74 different iron meteorites. New rare gas measurements are reported for some 40 samples. Results on the age, size and depth are obtained for almost 60 samples. These data suggest that Signer and Nier's model is well suited for describing not only the rare gas distribution in a single selected meteorite (Grant) but also the exposure histories of the great majority of all irons. For a few samples, however, secondary breakups of the meteoroid and a two- or multiple-stage irradiation must be invoked. Further measurements are proposed for testing and, possibly, refining the still somewhat uncertain relationships between the abundances of cosmogenic nuclides and the quantities T, S, and D in very large meteorites.Histograms are presented showing the age distributions for irons of different chemical groups and of different size ranges.The feasibility and the relative merits of other methods for the determination of T, S, and D are discussed.  相似文献   

2.
Pressure-induced phase transformations in each of the rutile-structured difluorides (NiF2, MgF2, CoF2, ZnF2, FeF2 and MnF2) exhibit unique behavior; however, a general trend is found in the major structural changes: rutile phase → “distorted fluorite” phase → post-“distorted fluorite” phase with volume changes of about 5–10%. For a given phase transformation sequence found commonly in two or more difluorides, the phase transformation pressure is related inversely to the unit cell volume and thus inversely to the mean cation-anion bond length. The relationship in oxides (SnO2, TiO2 and GeO2) is much less systematic. It is therefore not possible to predict without uncertainty the post-stishovite phases in the lower mantle.Velocity-density systematics in the difluorides and oxides are governed, to a large extent, by cationic radius. The pressure dependence of shear elastic constant CS = (C11 ? C12)/2 is negative in all of the nine difluorides and oxides. However, the CS mode does not vanish at the initial phase transformation pressure; rather, the ratios of CSKS are 0.10 and 0.04 to 0.10 for transitions of rutile → orthorhombic and of rutile → “distorted fluorite”, respectively, and are in agreement with the approach of Demarest et al.  相似文献   

3.
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4.
—?Seismic precursors to space shuttle re-entry shock fronts are detected at TXAR in Southwest Texas when the ground track of the orbiter vehicle passes within ～150–200?km of the observatory. These precursors have been termed “shuttle-quakes” because their seismograms superficially mimic the seismograms of small earthquakes from shallow sources. Analysis of the “shuttle-quake” seismograms, however, reveals one important difference. Unlike ordinary earthquakes, the propagation azimuths and horizontal phase velocities of the individual phases of the “shuttle-quakes” are functionally related. From a theoretical model developed to account for the origin of these precursors it is found that the seismic phases of “shuttle-quakes” are “bow” waves. A “bow” wave originates at the advancing tip of the shock front trace (i.e., intersection of the re-entry shock front with the surface of the earth) when the ground speed of the orbiter vehicle exceeds the horizontal phase velocity of a particular seismic phase. “Bow” waves are shown to differ in two important respects from the ordinary seismic phases. They vanish ahead of the advancing tip of the shock front trace and their propagation azimuths and horizontal phase velocities are functionally related. The ground speed of the orbiter vehicle exceeds the horizontal phase velocities of crustal seismic phase over much of the re-entry flight profile. As a result, P,S, and R g “bow” waves will be seen as precursors to the re-entry shock front at stations located within a few hundred km of its ground track.  相似文献   

5.
Abstract

A vortex-tube geometry of the cascade of energy to small-scale eddies, in the inertial range of fully-developed turbulence, is proposed. The model is a special case of the beta model of Frisch, Sulem and Nelkin (1978). We require that the cascade conserve the principal invariants of inviscid, incompressible flow, namely volume, topological knottedness, circulation, and, at discrete times marking the termination of steps in the cascade, energy. The process terminates in a finite time, as in any beta model, leaving behind a self-similar network of “inactive” tubes. We associate a self-similar scaling dimension D with the structure, equal to the Hausdorff dimension of the set of “active” tubes at the termination of the cascade. Because circulation Λ plays a key role in the analysis of the cascade, we refer to these vortex-tube geometries as “gamma models”. The viewpoint throughout is entirely deterministic.

We describe two examples of gamma models. In the ring geometry, an eddy is a vortex ring, and the cascade produces “rings upon rings”, so we allow cutting and fusing of tubes while conserving total helicity. In the preferred helical model, no cutting is needed, and the cascade produces an infinite progression of braided “coils upon coils”. We suggest that latter geometry as a candidate for the topology of a singularity of the inviscid limit of a Navier-Stokes flow, when modeled by discrete vortex tubes.

A crucial ingredient of a gamma model, not explicitly present in a beta model, is the possibility of “splitting” a vortex tube into sub-tubes carrying smaller circulation. We suggest a dynamical basis for this process, as an instability of tubes whose cores violate the Rayleigh criterion.

The parameters describing a gamma model are not uniquely determined by our study, but there is a “simplest” helical gamma model, involving minimal splitting and distortion of tubes. The dimension D of the structure is 13/5, with a scale factor Λ = 2?5/4. This value of D agrees with that suggested by Hentschel and Procaccia (1982), by analogy with established results for certain branched polymers.  相似文献   

6.
We characterize the heterogeneous source slip model of intraslab earthquakes to compare source scaling properties with those of inland crustal and subduction-zone plate-boundary earthquakes. We extracted rupture area (S), total area of asperity (S a), average slip (D) and average slip on asperity (D a) of eleven intraslab earthquakes following the procedure proposed by Somerville et al. (Seism Res Lett 70:59?C80, 1999) and proposed the empirical scaling relationship formula of S, S a, and D for intraslab earthquakes. Under the same seismic moment, an intraslab earthquake has a smaller rupture area and total area of asperity, and smaller average slip than an inland crustal earthquake. The area ratio of asperity area and total rupture area of intraslab earthquakes are similar to those of inland crustal earthquakes. The strong motion generation area (SMGA) scaling of intraslab earthquakes appears self-similar, and those results support the idea the characterized source model of intraslab earthquakes can be modeled in a manner similar to that of inland crustal earthquakes.  相似文献   

7.
The lack of knowledge concerning modelling existing buildings leads to significant variability in fragility curves for single or grouped existing buildings. This study aims to investigate the uncertainties of fragility curves, with special consideration of the single-building sigma. Experimental data and simplified models are applied to the BRD tower in Bucharest, Romania, a RC building with permanent instrumentation. A three-step methodology is applied： （1） adjustment of a linear MDOF model for experimental modal analysis using a Timoshenko beam model and based on Anderson＇s criteria, （2） computation of the structure＇s response to a large set of accelerograms simulated by SIMQKE software, considering twelve ground motion parameters as intensity measurements （IM）, and （3） construction of the fragility curves by comparing numerical interstory drift with the threshold criteria provided by the Hazus methodology for the slight damage state. By introducing experimental data into the model, uncertainty is reduced to 0.02 considering Sd ） as seismic intensity IM and uncertainty related to the model is assessed at 0.03. These values must be compared with the total uncertainty value of around 0.7 provided by the Hazus methodology.  相似文献   

8.
We developed an objective method to define the aftershock areas of large earthquakes as a function of time after the main shock. The definition is based upon the amount of energy released by aftershocks, the spatial distribution of the energy release is first determined and is contoured. The 1-day aftershock area is defined by a contour line corresponding to the energy release level of 1015.6 ergs/(100 km2 · day). The 10-day, 100-day and 1-y aftershock areas are similarly defined by contour lines corresponding to 1014.8, 1014.0, and 1013.5 ergs/(100 km2 · day), respectively. We also define the expansion ratios at time t by the ratio of the aftershock area at t to that at 1 day.Using this method we study the aftershock area expansion patterns of 44 large (Ms ? 7.5) and five moderate shallow earthquakes which occurred from 1963 to 1980. Each aftershock sequence is examined at four different times, i.e., 1 day, 10 days, 100 days, and 1 y after the main event. We define the aftershock area expansion ratios η and ηe by S(100)/S(1) and L(100)/L(1), respectively: here S(t) and L(t) are the area and the length of the aftershock area, respectively, at time t. Our study suggests that a distinct regional variation of aftershock area expansion patterns is present; it is strongly correlated with the tectonic environment. In general, the subduction zones of the “Mariana” type have large expansion ratios, and those of the “Chilean” type have small expansion ratios. Some earthquakes that occurred in the areas of complex bathymetry such as aseismic ridges tend to have large expansion ratios.These results can be explained in terms of an asperity model of fault zones in which a fault plane is represented by a distribution of strong spots, called the asperities, and weak zones surrounding the asperities. The rupture immediately after the main shock mostly involves asperities. After the main rupture is completed, the stress change caused by the main shock gradually propagates outward into the surrounding weak zones. This stress propagation manifests itself as expansion of aftershock activity. In this simple picture, if the fault zone is represented by relatively large asperities separated by small weak zones (“Chilean” type), then little expansion of aftershock activity would be expected. On the other hand, if relatively small asperities are sparsely distributed (“Mariana” type), significant expansion occurs. The actual distribution of asperities is likely to be more complex than the two cases described above. However, we would expect that the expansion ratio is in general proportional to the spatial ratio of the total asperity area to the fault area.  相似文献   

9.
Early Carboniferous (Viséan to possibly earliest Namurian) sedimentary rocks of the Deer Lake Group of western Newfoundland rest unconformably on Grenvillian basement rocks of the Canadian Shield which form the western border of the Early Palaeozoic Appalachian orogen. In addition to magnetically soft magnetizations directed along the present field, three families of magnetization directions are found. Two of them (referred to as N (north) and S (south)) are antiparallel and prefolding, and were probably acquired during the depositional process. N and S are roughly of equal frequency. They have a mean direction irrespective of sign of 0.7°, ?35.2°, k = 40, α95 = 8.9°, and a palaeopole 21.5°N, 121.8°E (10.3°, 6.0°) corresponding to a palaeolatitude of 20 ± 6°S. This agrees with the palaeolatitude (17 ± 5°S) determined from the somewhat older Early Carboniferous (Tournaisian) Terenceville Formation of the Avalon Platform on the eastern side of the Appalachian orogen in Newfoundland. The third magnetization, referred to as H (roughly horizontal), has a mean direction 156.8°, ?13.3°, k = 37, α95 = 10.1°, and a palaeopole 45.4°N, 140.3°E (10.3°, 5.3°) corresponding to a palaeolatitude of 7 ± 4°N; we interpret this to be an early Kiaman (latest Carboniferous to early Permian) overprint probably acquired chemically. The palaeolatitude determined from the H overprint agrees with that determined from Early Carboniferous rocks of cratonic North America west of the Appalachians. Therefore, we argue, Early Carboniferous palaeofield determinations for cratonic North America have been strongly biased by unremoved Kiaman overprints. Because of this, and because of the good agreement between Early Carboniferous palaeolatitudes obtained from opposite margins of the Appalachian orogen, we suggest that there is, at present, no palaeomagnetic evidence for the previously proposed 1500 km displacement from the south of an eastern portion of the Appalachians (“Acadia”) relative to cratonic North America during the Carboniferous.  相似文献   

10.
We calculated the fractal dimensions Db of the perimeter of tropical cyclone(TC)Dan based on the satellite GMS-5 infrared sensor images from 1800 UTC,1 October 1999 to 1200 UTC,9 October 1999.The fractal dimensions Db were used to characterize objectively the temporal change of TC complex structure.Our results show that the change of fractal dimension during TC Dan motion can be divided into three stages.The statistically significant difference does not exist either between Dm1 and DL or between Dm3 and DL,but it exists between Dm2 and DL,where Dmi denotes the mean value of Db in i-th stage(i=1,2 and3);DL denotes Lovejoy’s fractal dimension calculated based on satellite and radar data within the size range(1–1.2×106 km2),which is used as a"normal value"of the fractal dimension of the cumulus cloud perimeter for the global tropical region.TC Dan turns to the north from the west abruptly at the end of the second stage.The emergence of the second stage with high fractal dimensions may be viewed as a possible premonition for the track turning.Our results also show that there are two kinds of processes resulting in the translation from the first stage to the second stage.One is the interaction of TC circulation and an adjacent small scale convective cloud cluster,causing to the complexity increase of a local segment of the perimeter.The other includes the fragmentation of a strong convective area within the TC inner region,the self-organization of the small strong convective cloud clusters,the emergence,development,and merger of the small scale non-convective holes,and the formation of a gap of the perimeter,causing to the complexity increase of the whole TC perimeter.  相似文献   

11.
Since its formulation in 1967–1970, the classical ω ?2 model of earthquake source spectrum awaits a consistent theoretical foundation. To obtain one, stochastic elements are incorporated both into the final structure of the fault and into the mode of rupture propagation. The main components of the proposed “doubly stochastic” model are: (1) the Andrews’s concept, that local stress drop over a fault is a random self-similar field; (2) the concept of rupture with running slip pulse, after Heaton; (3) the hypothesis that a rupture front is a tortuous, multiply connected (“lacy”) fractal polyline that occupies a strip of finite width close to the slip-pulse width; and (4) the assumption that the propagation distance of fault-guided, mostly Rayleigh waves from a failing spot on a fault is determined by the slip-pulse width. Waveforms produced by this model are determined based on the fault asperity failure model after Das and Kostrov. Properties of the model are studied by numerical experiments. At high frequency, simulated source spectra behave as ω ?2, and acceleration spectra are flat. Their level, at a given seismic moment and rms stress drop, is inversely related to the relative width of the slip pulse. When this width is relatively low, a well-defined second corner frequency (lower cutoff of acceleration spectrum) is seen. The model shows clear dependence of propagation-related directivity on frequency. Between the first and the second corner frequency, amplitude spectra are strongly enhanced for the forward direction; whereas, above the second corner frequency, directivity is significantly reduced. Still, it is not inhibited totally, suggesting incomplete incoherence of the simulated radiator at high frequencies.  相似文献   

12.
In order to evaluate factors controlling transpiration of six common eastern deciduous species in North America, a model describing responses of canopy stomatal conductance (GS) to net radiation (RN), vapor pressure deficit (D) and relative extractable soil water (REW) was parameterized from sap flux data. Sap flux was measured in 24 mature trees consisting of the species Carya tomentosa, Quercus alba, Q. rubra, Fraxinus americana, Liriodendron tulipifera, and Liquidambar styraciflua in a bottomland oak-hickory forest in the Duke Forest, NC. Species differences in model coefficients were found during the 1997 growing season. All species showed a reduction in GS with increasing D. RN influenced GS in the overstory shade intolerant L. styraciflua to a larger extent than the other species measured. In addition, despite a severe drought during the study period, only L. tulipifera showed a decline in GS with decreasing REW. The primary effect of the drought for the other species appeared to be early autumn leaf senescence and abscission. As a result, despite the drought in this bottomland forest accustomed to ample water supply, maximum daily transpiration (1.6 mm) and growing season transpiration (264 mm) were similar to a nearby upland forest measured during a year of above average precipitation. These results may aid in assessing differences in water use and the ability of bottomland deciduous species to tolerate alterations in the frequency or amount of precipitation. Results also suggest little variation in water use among forests of similar composition and structure growing in different positions in the landscape and subjected to large interannual variation in water supply.  相似文献   

13.
Equations describing trace element and isotopic evolution in a magma chamber affected simultaneously by fractional crystallization and wallrock assimilation are presented for a model where the mass assimilation rate(?a) is an arbitrary fraction(r) of the fractional crystallization rate(?c). The equations also apply to recharge of a crystallizing magma. Relatively simple analytical expressions are obtained for both radiogenic isotope variations (Nd, Sr, Pb) and stable isotopes (O, H) including the effects of mass-dependent fractionation. Forr = 1 a modified zone refining equation is obtained for trace element concentrations, but forr < 1 behavior is a combination of zone refining and fractional crystallization. Asr → ∞, simple binary mixing is approached. The isotopic and trace element “mixing” trends generated can be much different from binary mixing, especially forr < 1. The model provides the basis for a more general approach to the problem of wallrock assimilation, and shows that binary mixing models are insufficient to rule out crustal assimilation as a cause of some of the isotopic variations observed in igneous rocks, including cases where clustering of isotopic values occurs partway between presumed endmember values. The coupled assimilation-fractional crystallization model provides an explanation for certain trace element and isotopic properties of continental margin orogenic magmas (e.g. Sr concentration versus87Sr/86Sr) which had previously been interpreted as evidence against assimilation. So-called “pseudoisochrons” can be understood as artifacts of contamination using this model. A significant correlation exists between country rock age and low143Nd/144Nd ratios in continental igneous rocks, clearly suggestive that crustal contamination is generally important.  相似文献   

14.
The 3-h Kp index is widely used as a measure of geomagnetic activity for ionospheric studies. Specifically, it is the planetary index used to determine the geomagnetic dependence of statistical auroral patterns and the convection electric field for certain models. Its quasi anti-logarithm, the Ap index, is similarly used in statistical models of the neutral atmosphere and neutral wind. Physics-based ionospheric models, such as the Utah State University (USU) Time-Dependent Ionospheric Model (TDIM), use these statistical models as magnetospheric and thermospheric inputs. However, the 3-h time interval between index computations is now considered a shortfall with regard to specifying and forecasting phenomena known to have faster time constants, e.g., auroral electrojet variations during a substorm. Therefore, these indices have been targeted for high-time resolution development; we have developed such indices in Della-Rose et al. (1999). We now use our 15-minute station “K-like” index to determine the effect of introducing high-time resolution magnetic fluctuations into the TDIM inputs. This study represented the high-latitude ionosphere by a grid of 1484 locations, and was carried out for a geomagnetic storm period during solar maximum and “simulated” winter solstice conditions. We found that, for fixed Interplanetary Magnetic Field (IMF) By/Bz ratio, driving the TDIM with our 15-minute “K-like” index altered the average high-latitude NmF2 value by as much as 8% (vs. the average NmF2 obtained using a 3-h index to drive the TDIM). More significantly, the standard deviation of the NmF2 variations was up to 35%. Under some conditions, the average NmF2 was changed by up to 30% with a standard deviation of over 60%. However, the effect of selecting different convection patterns that represented three southward IMF Bz orientations led to larger effects. The high-latitude average NmF2 changed by 10% or less, but the spread in the distribution always ranged from standard deviations of 29 to 68%. These results indicate that there is a substantial need to consider both short-term magnetic fluctuations and inclusion of real-time IMF data in the inputs to ionospheric models.  相似文献   

15.
Artificial recharge is a practical tool available for increasing the groundwater storage capacity. The efficiency of artificial recharge is related to various hydrogeological factors of the target area. In this study, a variable saturated groundwater flow model, FEMWATER, was used to evaluate the arrival times of recharged water that infiltrates from an artificial recharge pond to the groundwater table under various hydrogeological conditions. Forty-five arrival times were generated by FEMWATER. The relationships between the arrival times and hydrogeological factors used in the simulation of FEMWATER were analyzed by the grey correlation method. The results show the order of importance of the factors as they influence the arrival time. In order from high to low importance, they are α, D g, θ e, D p, K S and β. D g and D p are interpreted as the potential for movement of the recharge water; θe is the water storage capacity of soil, and K S represents the ability of soil to transport water. α and β describe the characteristic curve of the unsaturated soil. The method was applied to evaluate a suitable site for artificial recharge in the Yun-Lin area. Grey correlation analysis was performed to obtain the grey correlation grade using the minimum arrival time as a reference sequence. An index is proposed herein to determine the recharge efficiency of 20 sampling sites. A contour mapping of index values at the 20 sampling sites identified three areas for artificial aquifer recharge in Yun-Lin. Area A in the upper plain is considered more appropriate for groundwater recharge than areas B and C in the coast.  相似文献   

16.
High-precision Nb, Ta, Zr, Hf, Sm, Nd and Lu concentration data of depleted mantle rocks from the Balmuccia peridotite complex (Ivrea Zone, Italian Alps) were determined by isotope dilution using multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) and thermal ionisation mass spectrometry (TIMS). The Zr/Hf ratios of all investigated samples from the Balmuccia peridotite complex are significantly lower than the chondritic value of 34.2, and the most depleted samples have Zr/Hf ratios as low as 10. Correlated Zr/Hf ratios and Zr abundances of the lherzolites preserve the trend of a mantle residue that has been depleted by fractional melting. This trend confirms experimental studies that predict Hf to behave more compatibly than Zr during mantle melting. Experimentally determined partition coefficients imply that the major Zr and Hf depletion most likely occurred in the spinel stability field, with (DZr/DHf)cpx≈0.5, and not in the garnet stability field, where (DZr/DHf)grt is probably close to one. However, minor amounts of melting must have also occurred in a garnet facies mantle, as indicated by low Sm/Lu ratios in the Balmuccia peridotites. The Nb/Ta ratios of most lherzolites are subchondritic and vary only from 7 to 10, with the exception of three samples that have higher Nb/Ta ratios (18–24). The overall low Nb/Ta ratios of most depleted mantle rocks confirm a higher compatibility of Ta in the mantle. The uniform Nb/Ta ratios in most samples imply that even in ‘depleted’ mantle domains the budget of the highly incompatible Nb and Ta is controlled by enrichment processes. Such a model is supported by the positive correlation of Zr/Nb with the Zr concentration. However, the overall enrichment was weak and did barely affect the moderately incompatible elements Zr and Hf. The new constraints from the partitioning behaviour of Zr–Hf and Nb–Ta provide important insights into processes that formed the Earth’s major silicate reservoirs. The correlation of Zr/Hf and Sm/Nd in depleted MORB can be assigned to previous melting events in the MORB source. However, such trends were unlikely produced during continental crust formation processes, where Sm/Nd and Zr/Hf are decoupled. The different fractionation behaviour of Zr/Hf and Sm/Nd in the depleted mantle (correlated) and the crust (decoupled) indicates that crustal growth by a simple partial melting process in the mantle has little effect on the mass budget of LREE and HFSE between crust and mantle. A more complex source composition, similar to that of modern subduction rocks, is needed to fractionate the LREE, but not Zr/Hf and the HREE.  相似文献   

17.
Variants of the 2-D cellular model introduced by Olami, Feder, and Christensen (an analogue of the Burridge-Knopoff spring-block model) are examined. The influx of energy into each cell from the outside occurs at a constant rate. When the energy in a cell exceeds a certain threshold, the cell is “ruptured;” i.e., part of its energy, defined by the coefficient D, dissipates while the remainder is redistributed among the adjacent cells. The model is used to construct a catalog of clusters of ruptured cells. A method is proposed for estimating the dissipation coefficient D from the recurrence plot for a truncated catalog. In the range 0 ≤ D ≤ 0.35, D is estimated accurate to 0.01. The accuracy is improved with increasing lattice size.  相似文献   

18.
Nickel partitioning between olivine and silicate melt   总被引：1，自引：0，他引：1  
Partitioning of Ni between olivine and silicate melt has been determined for compositions in the system Fo-Ab-An (1 atm) for temperatures ranging from 1250°C to 1450°C. Nickel concentrations were determined by electron microprobe; concentration levels in the liquids ranged from 0.1% to 0.5%. Platinum capsules or Pt wire loops were used as containers. Equilibrium was evaluated from kinetic considerations and by variation of run parameters; it was documented in one case by a bracketed reversal. No evidence was found for a dependence of the partition coefficient D (Ni in olivine/Ni in liquid) on Ni concentration. D is strongly dependent on melt composition, varying linearly with (1/MgO) at constant temperature. The intrinsic temperature dependence of D is small; the apparent temperature dependence reported in previous studies is largely related to the variation of melt composition with temperature. Our D values determined in the simple system Fo-An-Ab agree well with those reported by Leeman for natural (Fe-bearing) basalt systems. Overall variation of D in our system (and in natural basalts) can be expressed by the regression: D = (124/MgO) ? 0.9Our data are used to evaluate published Ni-MgO relationships in natural basalt series from Kilauea, Crozet, Cape Verde and Baffin Bay. A combination of olivine accumulation and fractional crystallization processes are sufficient to model these series. Using our data, unique “parental” liquids can be specified for each of these series; the MgO content of these liquids varies from 6% to 13%. Basalts with MgO contents greater than these “parental” liquids must be accumulative. The linear Ni-MgO trends, high absolute Ni concentrations, and large spread of Ni contents for the high-MgO basalts argue convincingly against their being “primary” liquids. Models such as those of O'Hara [6,13] and Clarke [24], based on the assertion of primary high-MgO liquids, must therefore be re-evaluated.Because of the high Si/O ratio and low MgO content of island arc andesites, the Ni partition coefficient D may be quite high. Therefore, the relatively low Ni content of such andesites may not be an argument against their derivation as direct partial melts of the mantle.  相似文献   

19.
This paper examines temporal correlations and temporal clustering of a proxy historical landslide time series, 2255 reported landslides 1951–2002, for an area in the Emilia‐Romagna Region, Italy. Landslide intensity is measured by the number of reported landslides in a day (DL) and in an ‘event’ (Sevent) of consecutive days with landsliding. The non‐zero values in both time series DL and Sevent are unequally spaced in time, and have heavy‐tailed frequency‐size distributions. To examine temporal correlations, we use power‐spectral analysis (Lomb periodogram) and surrogate data analysis, confronting our original DL and Sevent time series with 1000 shuffled (uncorrelated) versions. We conclude that the landslide intensity series DL has strong temporal correlations and Sevent has likely temporal correlations. To examine temporal clustering in DL and Sevent, we consider extremes over different landslide intensity thresholds. We first examine the statistical distribution of interextreme occurrence times, τ, and find Weibull distributions with parameter γ << 1·0 [DL] and γ < 1·0 [Sevent]; thus DL and Sevent each have temporal correlations, but Sevent to a lesser degree. We next examine correlations between successive interextreme occurrence times, τ. Using autocorrelation analysis applied to τ, combined with surrogate data analysis, we find for DL linear correlations in τ, but for Sevent inconclusive results. However, using Kendall's rank correlation analysis we find for both DL and Sevent the series of τ are strongly correlated. Finally, we apply Fano Factor analysis, finding for both DL and Sevent the timings of extremes over a given threshold exhibit a fractal structure and are clustered in time. In this paper, we provide a framework for examining time series where the non‐zero values are strongly unequally spaced and heavy‐tailed, particularly important in the Earth Sciences due to their common occurrence, and find that landslide intensity time series exhibit temporal correlations and clustering. Many landslide models currently are designed under the assumption that landslides are uncorrelated in time, which we show is false. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
Boundary conditions can significantly affect a slope’s behavior under strong earthquakes. To evaluate the importance of boundary conditions for finite element (FE) simulations of a shake-table experiment on the slope response, a validated three-dimensional (3D) nonlinear FE model is presented, and the numerical and experimental results are compared. For that purpose, the robust graphical user-interface “SlopeSAR”, based on the open-source computational platform OpenSees, is employed, which simplifies the effort-intensive pre- and post-processing phases. The mesh resolution effect is also addressed. A parametric study is performed to evaluate the influence of boundary conditions on the FE model involving the boundary extent and three types of boundary conditions at the end faces. Generally, variations in the boundary extent produce inconsistent slope deformations. For the two end faces, fixing the y-direction displacement is not appropriate to simulate the shake-table experiment, in which the end walls are rigid and rough. In addition, the influence of the length of the 3D slope’s top face and the width of the slope play an important role in the difference between two types of boundary conditions at the end faces (fixing the y-direction displacement and fixing the (y, z) direction displacement). Overall, this study highlights that the assessment of a comparison between a simulation and an experimental result should be performed with due consideration to the effect of the boundary conditions.  相似文献   

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