Estimation or simulation? That is the question   总被引：1，自引：0，他引：1  

Jorge Kazuo Yamamoto 《Computational Geosciences》2008,12(4):573-591

The issue of smoothing in kriging has been addressed either by estimation or simulation. The solution via estimation calls for postprocessing kriging estimates in order to correct the smoothing effect. Stochastic simulation provides equiprobable images presenting no smoothing and reproducing the covariance model. Consequently, these images reproduce both the sample histogram and the sample semivariogram. However, there is still a problem, which is the lack of local accuracy of simulated images. In this paper, a postprocessing algorithm for correcting the smoothing effect of ordinary kriging estimates is compared with sequential Gaussian simulation realizations. Based on samples drawn from exhaustive data sets, the postprocessing algorithm is shown to be superior to any individual simulation realization yet, at the expense of providing one deterministic estimate of the random function.  相似文献   

Stochastic Modeling of Progressive Failure in Heterogeneous Soil Slope   总被引：1，自引：0，他引：1  

D. R. Pathak  H. N. Gharti  A. B. Singh  A. Hiratsuka 《Geotechnical and Geological Engineering》2008,26(2):113-120

Accurate and efficient simulation of the slope stability, certainly gives the reliable approach for the hazard preparedness. However, inherent difficulties associated with the slope failure make the situation very difficult. First, the computation of fracture path based on the strict mathematical formalism is cumbersome especially for the progressive failure phenomenon. Second, due to the lack of reliable knowledge on material properties, stochastic simulation is necessary. Stochastic modeling together with the progressive failure phenomenon is apparently difficult task. In this paper, heterogeneous slope is simulated considering the progressive failure phenomenon using the modified finite element method introducing the fracture along the edge of the meshes thus incorporating the time evolution of the fracture surface. This is achieved by restructuring the tessellation in every fracture stage. Unlike remeshing this technique only increases the number of total nodes while number of meshes remaining same, which is simple and natural. Further, in this research, effect of uncertainty in the material properties upon the uncertainty in the response of soil slope has been evaluated, hence giving the reliable probabilistic estimation of the factor of safety, failure surface and deformation of the slope. Thus the simulation based on the more reliable understanding of the material properties and the efficient numerical procedure for the progressive failure phenomenon can give the reliable result of the simulation for the heterogeneous soil slope thus enabling the more accurate way for hazard preparedness.  相似文献   

Investigating the preservation of orbital forcing in peritidal carbonates          下载免费PDF全文

David B. Kemp  Saskia M. Van Manen  David A. Pollitt  Peter M. Burgess 《Sedimentology》2016,63(6):1701-1718

Metre‐scale cycles in ancient peritidal carbonate facies have long been thought to represent the product of shallow water carbonate accumulation under orbitally controlled sea‐level oscillations. The theory remains somewhat controversial, however, and a contrasting view is that these cycles are the product of intrinsic, and perhaps random, processes. Owing to this debate, it is important to understand the conditions that do, or do not, favour the preservation of orbital forcing, and the precise stratigraphic expression of that forcing. In this work, a one‐dimensional forward model of carbonate accumulation is used to test the ability of orbitally paced sea‐level changes to reconstruct cyclicities and cycle stacking patterns observed in greenhouse peritidal carbonate successions. Importantly, the modelling specifically tests insolation‐based sea‐level curves that probably best reflect the pattern and amplitude of sea‐level change in the absence of large‐scale glacioeustasy. This study found that such sea‐level histories can generate precession and eccentricity water depth/facies cycles in models, as well as eccentricity‐modulated cycles in precession cycle thicknesses (bundles). Nevertheless, preservation of orbital forcing is highly sensitive to carbonate production rates and amplitudes of sea‐level change, and the conditions best suited to preserving orbital cycles in facies/water depth are different to those best suited to preserving eccentricity‐scale bundling. In addition, it can be demonstrated that the preservation of orbital forcing is commonly associated with both stratigraphic incompleteness (missing cycles) and complex cycle thickness distributions (for example, exponential), with corresponding implications for the use of peritidal carbonate successions to build accurate astronomical timescales.  相似文献   

Diurnal-inertial motions and diapycnal mixing on the Portuguese shelf     

Borja Aguiar-González  Ángel Rodríguez-Santana Jesús Cisneros-Aguirre  Antonio Martínez-Marrero 《Continental Shelf Research》2011,31(11):1193-1201

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Stochastic simulation of spatially correlated geo-processes     

George Christakos 《Mathematical Geology》1987,19(8):807-831

In this study, developments in the theory of stochastic simulation are discussed. The unifying element is the notion of Radon projection in Euclidean spaces. This notion provides a natural way of reconstructing the real process from a corresponding process observable on a reduced dimensionality space, where analysis is theoretically easier and computationally tractable. Within this framework, the concept of space transformation is defined and several of its properties, which are of significant importance within the context of spatially correlated processes, are explored. The turning bands operator is shown to follow from this. This strengthens considerably the theoretical background of the geostatistical method of simulation, and some new results are obtained in both the space and frequency domains. The inverse problem is solved generally and the applicability of the method is extended to anisotropic as well as integrated processes. Some ill-posed problems of the inverse operator are discussed. Effects of the measurement error and impulses at origin are examined. Important features of the simulated process as described by geomechanical laws, the morphology of the deposit, etc., may be incorporated in the analysis. The simulation may become a model-dependent procedure and this, in turn, may provide numerical solutions to spatial-temporal geologic models. Because the spatial simlation may be technically reduced to unidimensional simulations, various techniques of generating one-dimensional realizations are reviewed. To link theory and practice, an example is computed in detail.  相似文献   

Stochastic modeling of Iranian earthquakes and estimation of ground motion for future earthquakes in Greater Tehran     

Hamid Zafarani  Assadollah NoorzadAnooshirvan Ansari  Khosro Bargi 《Soil Dynamics and Earthquake Engineering》2009

Strong-motion data from eight significant well-documented earthquakes in Iran have been simulated using a stochastic modeling technique for finite faults proposed by Beresnev and Atkinson [Bull Seismol Soc Am 87 (1997) 67–84; Seism Res Lett 69 (1998) 27–32]. The database consists of 61 three-component records from eight earthquakes of magnitude ranging from M 6.3 to M 7.4, recorded at hypocentral distances up to 200 km. The model predictions are in good agreement with available Iranian strong-motion data as evidenced by near-zero average of differences between logarithms of the observed and predicted values for all frequencies. The strength factor, sfact, a quantity that controls the high-frequency radiation from the source is determined, on an event-by-event basis, by fitting simulated to observed response spectra.  相似文献   

RESPONSE OF THE OCEAN UPPER MIXED LAYER TO ATMOSPHERIC FORCING   总被引：1，自引：0，他引：1  

刘秦玉 《中国海洋湖沼学报》1994,12(3):280-283

Using a one-dimension Turbulence Kinetic Energy(TKE)mixed layer model based on a simple eddyKinetic energy parameterization of the ocean upper mixed layer,some numerical examinations are intro- duced in this paper.These examination results show that the TKE ocean mixed layer model can respondwell to the effect of atmospheric forcing on the ocean upper mixed layer.The joint effect of wind stressand heat exchange on the ocean upper layer has nonlinear characteristics.The adjustment time of the re-sponse of the ocean upper mixed layer to the atmospheric forcing is about 12 hours in this model.  相似文献   

Stochastic prediction in geomorphology using Bayesian inference models     

George A. Griffiths 《Mathematical Geology》1982,14(1):65-75

Bayesian inference modeling may be applied to empirical stochastic prediction in geomorphology where outcomes of geomorphic processes can be expressed by probability density functions. Natural variations in process outputs are accommodated by the probability model. Uncertainty in the values of model parameters is reduced by considering statistically independent prior information on long-term, parameter behavior. Formal combination of model and parameter information yields a Bayesian probability distribution that accounts for parameter uncertainty, but not for model uncertainty or systematic error which is ignored herein. Prior information is determined by ordinary objective or subjective methods of geomorphic investigation. Examples involving simple stochastic models are given, as applied to the prediction of shifts in river courses, alpine rock avalanches, and fluctuating river bed levels. Bayesian inference models may be applied spatially and temporally as well as to functions of a random variable. They provide technically superior forecasts, for a given shortterm data set, to those of extrapolation or stochastic simulation models. In applications the contribution of the field geomorphologist is of fundamental quantitative importance.  相似文献   

海气耦合随机模式中随机项的处理     

唐佑民  郭岚 《成都信息工程学院学报》1990,(Z1)

本文对海气相互作用随机动力模式中随机项的处理作了探讨,分析了目前对随机项的简单处理而产生的问题,在此基础上,对随机项处理进行了重新认识和改进,并由此解释了相应合理的模式解。  相似文献   

Modelling Thermohaline Properties in an Estuarine Upwelling Ecosystem (R?́a de Vigo: NW Spain) Using Box-Jenkins Transfer Function Models     

E. Nogueira  F.F. Pérez  A.F. R?&#x;os 《Estuarine, Coastal and Shelf Science》1997,44(6):685-702

Since 1987, twice weekly, hydrological variables have been monitored at a fixed station in the R?́a de Vigo (NW Spain), aiming to examine the time scales of variability and the relationships to meteorological conditions. The present paper analyses: (1) the advantage of Box-Jenkins transfer function (TF) models (single output–multiple input), a type of linear stochastic model, to describe the dynamic behaviour of the system; and (2) the coupling between the R?́a and meteorological events at the time scale of autonomy of this coastal inlet affected by the Iberian coastal upwelling, approximately a fortnightly period. In order to achieve these objectives, thermohaline properties have been used to characterize the estuarine ecosystem (output variables), while wind regime, runoff in the drainage basin and incoming solar radiation have been considered as the main forcing variables (input variables). The use of the amplitude time series, derived from principal component analysis (PCA) applied to the deseasonalized meteorological variables, is also explored as a different set of input variables.When compared with standard regression models, all TF models built to describe thermohaline behaviour had reduced residual variance. Similar TF models, as well as percentage of explained variance, were also obtained when meteorological variables or the amplitude time series were used as input variables. The fitted TF models provided an insight into the ‘ inertial ’ behaviour of the system and the time scales of coupling of the system with the forcing variables. The plausible physical mechanisms which link the response of the system with the observed meteorological variability are also discussed. As could be expected, bottom thermohaline properties show a stronger inertial behaviour than the surface ones, which is particularly marked for bottom temperature. Besides, the shelf domain, by means of upwelling-downwelling events, strongly influences surface and bottom temperature, as well as bottom salinity; by contrast, surface salinity is mainly influenced by the effect of wind along the main axis of the R?́a and runoff. In relation to the time scales of coupling between the system and the forcing variables, thermohaline properties show a dependance with the meteorological conditions in, at least, the immediately preceding fortnight period. It was concluded that: (1) TF models that incorporate meteorological information described the dynamic behaviour of the system adequately; and (2) this type of model can be useful as a first approximation to develop more sophisticated (deterministic) models, since, with the purpose of modelling any state variable of the system, both the coupling between different domains and the time scales of the interactions must be taken into account.  相似文献