地震层析成像中的不确定性   总被引：1，自引：0，他引：1  

安美建  冯梅  赵琳 《CT理论与应用研究》2009,18(2):24-32

地震层析成像已经是一种常用的探测地球内部三维波速结构的地球物理方法。这些深部地球结构信息是人们深入认识地球的重要依据,同时由于地表地质过程往往取决于深部动力过程,因此深部结构已经开始受到了地质学家们的广泛重视。但地震层析成像方法众多,所得到的参数和精度可能有所不同,这给非地震学专业的研究人员在使用层析成像结果的过程中造成了极大的不便。为了更好地实现地球物理,地球化学和地质等多学科交叉应用,本文系统分析了地震层析成像结果中可能存在的不确定性,同时提出了相应的建议以帮助地质学家们能够正确对待层析成像结果中的不确定性并合理利用地震层析成像结果。  相似文献   

随机模型上的地震动模拟研究     

余嘉顺  唐红  谢显中 《地震研究》2005,28(1):58-63

介绍了一项随机模拟实验,该实验通过模拟一个具体场址模型的地震动响应了解模型参数不确定性对模拟结果的影响。首先给定一个典型的第四纪沉积层场址模型的参数(包括地层厚度、介质密度、横波速度和品质因子等)的统计特征,并据此在计算机上按截尾的正态分布随机抽样形成了16384个随机模型,然后分别在各个模型上进行SH波地震动响应模拟,最后对所有的模拟结果进行统计分析,了解模型参数的不确定程度与模拟结果变化范围之间的关系。实验结果表明,模型参数不确定性对模拟结果的影响程度是随频率增大的。随机模型地震动响应的第一个放大峰发生在353±031Hz的频率上,其幅值为438±076;第二放大峰发生在885±108Hz的频率上,幅值为422±090。两放大峰值的均方差与均值之比分别为18%和25%。与模型参数20%的相对变化程度大致相当。但更高频率上振幅响应的均方差与均值之比则高达30%～40%。  相似文献   

数值预报发展的新方向——集合数值预报   总被引：6，自引：1，他引：5  

王太微  陈德辉 《气象研究与应用》2007,28(1):6-12

数值预报走过了百年的历史(V.Bjerknes,1904)[1],取得了了不起的成就,预报准确率有了很大的提高。但是,考虑到大气的非线性作用以及初值和模式造成的数值预报不确定性,要提高传统的单一确定性预报的技巧越来越难。基于大气初值的敏感性试验,Lorenz提出了数值预报发展的新方向——集合数值预报。通过介绍集合数值预报的基本思想和方法;并针对初值和模式的不确定性,概述现有集合数值预报成员的产生方法及国内外的研究进展;同时解释怎样检验集合预报的结果的论述,如何从众多的集合预报产品中提炼有用的信息及预报产品的释用。  相似文献   

GGR Critical Review of Analytical Developments in 2006–2007     

Janet M. Hergt  L. Paul Bédard  Stefanie M. Brueckner  Klaus Peter Jochum  Kathryn L. Linge  Paul J. Sylvester  Michael Wiedenbeck  Jon D. Woodhead 《Geostandards and Geoanalytical Research》2008,32(4):397-398

In 2005 the Geostandards and Geoanalytical Research editorial team, in the true spirit of scientific endeavour, embarked on an experiment of our own. We decided to trial a new kind of review, somewhat different from those more typically observed in journals, and one that would provide readers with a summary of analytical developments across a broad range of topics appropriate to the Earth sciences. The first contribution of this kind appeared in 2005, and reported on developments in 2003 (Hergt et al. 2005). The second, this time a biennial review, was published in 2006 and reported on highlights of the 2004 and 2005 literature (Hergt et al. 2006). Based on reprint requests, positive remarks at conferences and strong citations we consider the experiment a resounding success and proudly present here the third in this series. This comprises six individual review sections that cover the main analytical technologies and topical application fields in geoanalysis and geochemistry, including geological and environmental reference materials, ICP‐thermal and secondary ionisation‐mass spectrometry, as well as neutron activation analysis, X‐ray fluorescence and atomic absorption spectrometry.  相似文献   

The Uncertainty of Mesoscale Numerical Prediction of Heavy Rain in South China and the Ensemble Simulations?          下载免费PDF全文

CHEN Jing  XUE Jishan  YAN Hong 《Acta Meteorologica Sinica》2005,19(1):1-18

In the context of non-hydrostatic MM5 version we have explored the impact of convective parameterization schemes on uncertainty in mesoscale numerical prediction of South China heavy rain and mesoscale heavy rainfall short-range ensemble simulation by using two kinds of physics perturbation methods through a heavy rain case occurring on June 8, 1998 in Guangdong and Fujian Provinces. The results show the physical process of impacts of convective schemes on heavy rainfall is that different latent heat of convective condensation produced by different convective schemes can make local temperature perturbation, leading to the difference of local vertical speed by the intrinsic dynamic and thermodynamic processes of atmosphere,and therefore, making difference of the timing, locations and strength of mesh scale and subgrid scale precipitation later. New precipitations become the new source of latent heat and temperature perturbation,which finally make the dynamic and thermodynamic structures different in the simulations. Two kinds of methods are used to construct different model version stochastically. The first one is using different convective parameterization and planetary boundary layer schemes, the second is adjusting different parameters of convective trigger functions in Grell scheme. The results indicate that the first ensemble simulations can provide more uncertainty information of location and strength of heavy rainfall than the second. The single determinate predictions of heavy rain are unstable; physics ensemble predictions can reflect the uncertainty of heavy rain, provide more useful guidance and have higher application value.Physics ensembles suggest that model errors should be taken into consideration in the heavy rainfall ensembles. Although the method of using different parameters in Grell scheme could not produce good results, how to construct the perturbation model or adjust the parameter in one scheme according to the physical meaning of the parameter still needs further investigation. The limitation of the current study is that it is based on a single case and more cases will be addressed in the future researches.  相似文献   

Non‐ergodicity and PEER's framework formula     

Armen Der Kiureghian 《地震工程与结构动力学》2005,34(13):1643-1652

A framework formula for performance‐based earthquake engineering, advocated and used by researchers at the Pacific Earthquake Engineering Research (PEER) Center, is closely examined. The formula was originally intended for computing the mean annual rate of a performance measure exceeding a specified threshold. However, it has also been used for computing the probability that a performance measure will exceed a specified threshold during a given period of time. It is shown that the use of the formula to compute such probabilities could lead to errors when non‐ergodic variables (aleatory or epistemic) are present. Assuming a Poisson model for the occurrence of earthquakes in time, an exact expression is derived for the probability distribution of the maximum of a performance measure over a given period of time, properly accounting for non‐ergodic uncertainties. This result is used to assess the approximation involved in the PEER formula for computing probabilities. It is found that the PEER approximation of the probability has a negligible error for probabilities less than about 0.01. For larger probabilities, the error depends on the magnitude of non‐ergodic uncertainties and the duration of time considered and can be as much as 20% for probabilities around 0.05 and 30% for probabilities around 0.10. The error is always on the conservative side. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Site-specific prediction of West Nile virus mosquito abundance in Greater Toronto Area using generalized linear mixed models     

Eun-Hye Yoo 《International journal of geographical information science》2014,28(2):296-313

Mosquito surveillance programs provide a primary means of understanding mosquito vector population dynamics for the risk assessment of human exposure to West Nile virus (WNv). The lack of spatial coverage and missing observations in mosquito surveillance data often challenge our efforts to predict this vector-borne disease and implement control measures. We developed a WNv mosquito abundance prediction model in which local meteorological and environmental data were synthesized with entomological data in a generalized linear mixed modeling framework. The discrete nature of mosquito surveillance data is accommodated by a Poisson distributional assumption, and the site-specific random effects of the generalized linear mixed model (GLMM) capture any fluctuation unexplained by a general trend. The proposed Poisson GLMMs efficiently account for the nested structure of mosquito surveillance data and incorporate the temporal correlation between observations obtained at each trap by a first-order autoregressive model. In the case study, Bayesian inference of the proposed models is illustrated using a subset of mosquito surveillance data in the Greater Toronto Area. The relevance of the proposed GLMM tailored to WNv mosquito surveillance data is highlighted by the comparison of model performance in the presence of inevitable but quantifiable uncertainties.  相似文献   

Partitioning evapotranspiration fluxes into soil evaporation and plant transpiration using water stable isotopes under controlled conditions   总被引：1，自引：0，他引：1  

Youri Rothfuss  Philippe Biron  Isabelle Braud  Laurent Canale  Jean‐Louis Durand  Jean‐Paul Gaudet  Patricia Richard  Michel Vauclin  Thierry Bariac 《水文研究》2010,24(22):3177-3194

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Influence of spatial variability of soil friction angle on sheet pile walls’ structural behaviour     

Humberto Yáñez-Godoy  Abdelhammid Mokeddem  Sidi Mohammed Elachachi 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2017,11(4):299-314

The uncertainty in terms of soil characterisation is studied to assess its effect on the structural behaviour of extended structures as sheet pile walls. A finite element model is used. This integrates a numerical model of the soil–structure interaction together with a stochastic model that allows characterising the soil variability. The model serves in propagating the variability and the system parameter uncertainties. Discussion is mainly focused on two points: (1) testing the sensitivity of the structural behaviour of a sheet pile wall to different geotechnical parameters and (2) assessing the influence of spatial variability of soil properties on the structural behaviour by identifying the most sensitive geotechnical parameter and the most significant correlation length values. The findings showed that in assessing the sheet pile wall’s structural behaviour, there are spatial variability parameters that cannot be considered negligible. In this study, soil friction angle is found to be an important parameter.  相似文献   

Stochastic evolution of hydraulic geometry relations in the lower Yellow River of China under environmental uncertainties     

《国际泥沙研究》2020,35(4):328-346

Hydraulic geometry relations comprise a classic way to understand characteristics of a river. However, environmental changes pose large uncertainties for the reliability of such relations. In the current study, on the basis of the ordinary differential equations (ODEs) formed through linear treatment of the deterministic power-law hydraulic geometry relations, a set of stochastic differential equations (SDEs) driven by Fractional white noise and Poisson noise are developed to simulate the historical dynamic probability distributions of typical hydraulic geometry variables such as slope, width, depth, and velocity with bankfull discharge variation over time in the lower Yellow River of China. One group of possible stochastic average behaviors within the next 50 years are calculated under three different design incoming water-sediment conditions (including 300, 600, and 800 million t of annual average sediment discharge). In each part of the lower reaches, after estimation of the SDE parameters using a nonparametric maximum likelihood estimation (MLE) method, the model is carefully examined using Monte Carlo simulation as compared with the deterministic control models. The results of this comparison reveal the potential responses of hydraulic geometry characteristics to environmental disturbances, and the average trends mainly agree with the measurements. Comparisons among the three different prediction results reveal the stochastic average solution generally is greater than the deterministic solution. The results also confirm the severe negative impacts that result from the condition of 300 million t of incoming sediment, thus, pointing out the need to raise the level of river evolution alert for the lower Yellow River of China in the future. Moreover, with the help of the stochastic computation, the stream power and hydraulic width/depth ratio could be representative of an effective systematic measure for river dynamics. The proposed stochastic approach is not only important to development in the field of fluvial relations, but also beneficial to the practical design and monitoring of a river system according to specified accuracy requirements.  相似文献