共查询到20条相似文献，搜索用时 31 毫秒
1.
In this paper, we present three diverse types of applications of extreme value statistics in geology, namely: earthquakes magnitudes, diamond values, and impact crater size distribution on terrestrial planets. Each of these applications has a different perspective toward tail modeling, yet many of these phenomena exhibit heavy or long tails which can be modeled by power laws. It is shown that the estimation of important tail characteristics, such as the extreme value index, is directly linked to the interpretation of the underlying geological process. Only the most extreme data are useful for studying such phenomena, so thresholds must be selected above which the data become power laws. In the case of earthquake magnitudes, we investigate the use of extreme value statistics in predicting large events on the global scale and for shallow intracontinental earthquakes in Asia. Large differences are found between estimates obtained from extreme value statistics and the usually applied standard statistical techniques. In the case of diamond deposits, we investigate the impact of the most precious stones in the global valuation of primary deposits. It is shown that in the case of Pareto-type behavior, the expected value of few extreme stones in the entire deposit has considerable influence on the global valuation. In the case of impact crater distributions, we study the difference between craters distributions on Earth and Mars and distributions occurring on other planets or satellites within the solar system. A striking result is that all planets display the same distributional tail except for Earth and Mars. In a concluding account, we demonstrate the apparent loghyperbolic variation in all of the above-mentioned examples. 相似文献
2.
利用海河流域实测和调查年最大点暴雨、实测大面积暴雨和气象等资料,分析了年极端点暴雨的季节变化、特征和地区分布、大面积暴雨特征以及形成极端暴雨的天气成因,揭示了极端暴雨发生的基本规律。结果表明,流域暴雨9成以上集中在7~8月,极端暴雨7成高度集中在7月下旬到8月上旬;极端暴雨集中分布在太行山~燕山山脉的迎风山区;短历时小面积极端暴雨则分布在高原区;极端暴雨的年际变率迎风山区最大,平原和高原区较小;流域性极端暴雨高空环流多为经向型,通过中纬度西风槽、副热带高压或台风等天气系统以及迎风山区地形抬升作用共同造成。 相似文献
3.
On tail estimation: An improved method 总被引：1，自引：0，他引：1
G. R. Dargahi-Noubary 《Mathematical Geology》1989,21(8):829-842
A step is described toward better statistical treatment of data for tail estimation. The classical extreme value theory together with its practical inefficiency for tail inference are discussed briefly. The threshold method that utilizes available information in a more efficient manner is described, and its relation to extreme value theory is mentioned. Some comparison is also made using two sets of published data. 相似文献
4.
研究基于高阶概率权重矩的广义极值分布参数估计。根据高阶概率权重矩法原理,建立了广义极值分布高阶概率权重矩估算参数模型。以陕北地区4个水文测站的年最大洪峰流量序列为例,结果表明:高阶概率权重矩法能赋予大洪水值更多的权重。蒙特卡洛试验表明:适当提高阶数可以减小误差,但阶数过高反而会增大误差。 相似文献
5.
本文研究了前期冬季北极海冰与中国东部春季极端降水频次的联系及其可能机制,并进一步探讨了海冰异常信号对极端降水的预测价值。结果表明,前冬戴维斯海峡—巴芬湾区域海冰异常与中国东部春季极端降水频次经验正交分解第一模态(EOF1)之间存在密切联系。当前冬戴维斯海峡—巴芬湾区域海冰异常偏多时,冬季大气环流呈现出类北大西洋涛动(NAO)正位相的异常分布,并伴随经向的北大西洋三极型海温异常。该海温异常可以从冬季持续到春季,进而激发出从北大西洋到欧亚中纬度的纬向遥相关波列,在东亚地区引起气旋型环流异常。该气旋型环流异常会引起中国东部地区湿度显著增加,上升运动增强,从而为该地区极端降水的发生提供了有利的背景条件。相反,当前冬戴维斯海峡—巴芬湾区域海冰异常偏少时,其滞后引起的春季环流异常则不利于中国东部地区极端降水的发生。进一步的交叉检验结果表明,前冬戴维斯海峡—巴芬湾区域海冰异常信号对中国东部春季极端降水具有重要的预测价值。 相似文献
6.
Extreme value analysis provides a semiparametric method for analyzing the extreme long tails of skew distributions which may be observed when handling mining data. The estimation of important tail characteristics, such as the extreme value index, allows for a discrimination between competing distribution models. It measures the thickness of such long tailed distributions, if only a limited sample is available. This paper stresses the practical implementation of extreme value theory, which is used to discriminate a lognormal from a mixed lognormal distribution in a case study of size distributions for alluvial diamonds. 相似文献
7.
Strong wind and rainfall induced by extreme meteorological processes such as typhoons have a serious impact on the safety of bridges and offshore engineering structures. A new bivariate compound extreme value distribution is proposed to describe the probability dependency structure of annual extreme wind speed and concomitant process maximum rainfall intensity in typhoon-affected area. This probability model takes full account of the case that there may be no rainfall in a typhoon process. A case study based on the observation data of typhoon maximum wind speed and maximum rainfall intensity in Shanghai is conducted to testify the efficiency of the model. Weibull distributions with two parameters are applied to fit respective probability margins, and the joint probability distribution is constructed by Gumbel–Hougaard copula. The fitting results and K–S tests show that these models describe the original data well. The joint return periods are calculated by Poisson bivariate compound extreme value distribution we have proposed. They indicate that typhoons with no rain have smaller joint return periods, and wind speed is the main factor which impacts the change of the joint return periods. 相似文献
8.
论述极值统计推断不可靠的表现、产生原因及提高可靠性的途径、可操作性方法和可靠性评价。提出收敛域准则、极大似然估计的精估计和粗估计、泛似然估计、多母体现象,应用超拟合现象、抽样误差、蒙特卡罗随机模拟等概念或方法,得出全国各气象站多个气象要素的可靠极值统计推断结果,初步形成小样本统计理论。 相似文献
9.
高寒内流区极端降水的气候变化特征分析 总被引：1，自引：1，他引：0
利用中国气象局1969—2017年高寒内流区25个气象站的日降水资料,分析极端降水的变化特征,结果表明：1969—2017年高寒内流区降水量呈上升趋势,这种上升很大程度上可能是由于夏季降水量增加导致的,且20世纪90年代以后降水量增加趋势更加明显。极端降水指数除连续干旱日数外,均呈不同程度的增加趋势,其年际变化反映出在进入21世纪后高寒内流区降水向强降水量和日数更多、强度更强、极值更大的方向发展。极端降水指数空间差异性明显,连续湿润日数、雨日降水总量、雨日降水强度、单日最大降水量、五日最大降水量、极端降水量和日降水大于10 mm日数表现显著增加趋势的台站百分率分别为5%、64%、42%、60%、32%、35%和43%,连续干旱日数表现显著下降趋势的台站百分率为5%。极端降水事件具有一致性,总降水量增加,极端降水的频率、强度、极值也增加,小雨日数增加是降水总量增加的因素之一。极端降水增湿幅度有随海拔升高有增大趋势,高海拔区雨日降水量和雨日天数的增加是极端降水总量增加的主要因素。 相似文献
10.
11.
Fagnant Carlynn Gori Avantika Sebastian Antonia Bedient Philip B. Ensor Katherine B. 《Natural Hazards》2020,104(2):1597-1621
Natural Hazards - Rainfall extreme value analysis provides information that has been crucial in characterizing risk, designing successful infrastructure systems, and ultimately protecting people... 相似文献
12.
Many natural phenomena exhibit size distributions that are power laws or power law type distributions. Power laws are specific in the sense that they can exhibit extremely long or heavy tails. The largest event in a sample from such distribution usually dominates the underlying physical or generating process (floods, earthquakes, diamond sizes and values, incomes, insurance). Often, the practitioner is faced with the difficult problem of predicting values far beyond the highest sample value and designing his system either to profit from them, or to protect against extreme quantiles. In this paper, we present a novel approach to estimating such heavy tails. The estimation of tail characteristics such as the extreme value index, extreme quantiles, and percentiles (rare events) is shown to depend primarily on the number of extreme data that are used to model the tail. Because only the most extreme data are useful for studying tails, thresholds must be selected above which the data are modeled as power laws. The mean square error (MSE) is used to select such thresholds. A semiparametric bootstrap method is developed to study estimation bias and variance and to derive confidence limits. A simulation study is performed to assess the accuracy of these confidence limits. The overall methodology is applied to the Harvard Central Moment Tensor catalog of global earthquakes. 相似文献
13.
Until recently, research on potential economic impacts of climate change and extreme weather events on transport infrastructure was scarce, but currently this area is rapidly expanding. Indeed, there is a growing international interest, including the European area, regarding the impacts of extreme weather and climate change on the management of various transportation modes. This paper reviews briefly the present status regarding the knowledge of financial aspects of extreme weather impacts on transportation, using recent research findings from Europe, and proposes some new views in cost-benefit analysis, project appraisal and asset value protection for the management of transport systems under extreme weather risks. Quite often, risk management is understood as a response to truly extreme impacts, but this constitutes a misunderstanding. Some values are more extreme than others, and in the context of extreme weather, some weather phenomena are more extreme in their intensity and resulting impacts. An analysis of the level of costs and risks to societies, as a result of extreme weather, reveals that the risks in different European Union member states deviate substantially from each other. Also, the preparedness of different societies to deal with extreme weather events is quite variable. Extreme weather and climate change costs and risks represent a new type of item, which has to be dealt with in project appraisal. Although a fully established procedure does not exist, some fundamental ideas of cost-benefit analysis under extreme weather scenarios are presented in this paper, considering accident costs, time costs and infrastructure-related costs (comprising physical damages to infrastructures and increased maintenance costs). Cost-benefit analysis is usually associated with capital investments, but the original idea of cost-benefit analysis is not restricted to investment appraisal. Therefore, activities such as enhanced maintenance, minor upgrades, adoption of new designs, improved information services and others may be subject to cost-benefit analysis. Extreme weather and climate change costs and risks represent a new type of item, which apparently has to be dealt with also in project appraisal. A fully established procedure does not exist, although some basic principles have been introduced in analytical format. There is a lack of models to estimate extreme weather impacts and consequences and how to adapt to those costs. Optimising the efforts in maintenance and new design standards is even further away, but constitutes an overwhelming task. In this respect, new approaches and ways of thinking in preserving asset’s residual value, return periods, sustainability and equity and formal methods supplementing cost-benefit analysis are put forward. The paper concludes with a call for the need for more integrated management of transport systems. In particular, it is recognised that the different stages of transport system planning pose their own challenges when assessing the costs and benefits of policy measures, strategies and operational decisions. 相似文献
14.
The classical extreme value theory based on generalized extreme value (GEV) distribution and generalized Pareto distribution (GPD) is applied to the wave height estimate based on wave hindcast data covering a period of 31?years for a location in the eastern Arabian Sea. Practical concern such as the threshold selection and model validation is discussed. Estimates of wave height having different return periods are compared with estimates obtained from different distributions. On comparing the distributions fitted to the GEV with annual maximum approach and GPD with peaks over threshold approach have indicated that both GEV and GPD models gave similar or comparable wave height for the study area since there is no multiple storm event in a year. Influence of seasonality on wave height having different return period is also studied. 相似文献
15.
倾斜断层Vzz、Vzzz的联合反问题解 总被引：1，自引：0，他引：1
本文利用两个上延高度的Vzz极值距和其中之一高度的Vzzz的零值点获得了倾斜断层的位置、埋深、断距、倾向、倾角以及断层正逆性质等的反问题解。 相似文献
16.
为了科学评估变化环境下城市地区降水结构变化和深入认识特大型城市降水极值演变特征,以北京市为例,采用《北京市暴雨图集》中6种历时（10 min、30 min、1 h、6 h、24 h和72 h）的年最大暴雨统计数据和北京地区45个雨量站点1960-2012年汛期（6-9月）逐日降水观测资料,分别选择年最大值法和百分位阈值法,基于暴雨图集中的6种历时暴雨的统计特征值和两种百分位阈值下（95%和99%）的3种极端降水指标（发生次数、降水量和降水贡献率）分析北京地区降水极值的时空变化特征。研究结果表明:① 北京地区降水极值的空间分布受地形特征和城市化发展等因素影响而呈现出从东向西递减的趋势,且形成了局部区域高值中心;② 近50年来北京地区极端降水发生频次、极端降水量和极端降水的贡献率均表现出显著的下降趋势,在95%（99%）阈值条件下极端降水发生次数、极端降水量和极端降水贡献率的下降速率分别为0.13次/10 a（0.04次/10 a）、11.59 mm/10a（5.28 mm/a）和2%/10 a（1%/10 a）;③ 两个阶段（1960-1985年和1986-2012年）的城区与近郊的极端降水指标差异表现不同,1960-1985年在极端降水频次方面郊区占优,而极端降水量和贡献率则是城区较高,1986-2012年3个指标均表现为城区较高。 相似文献
17.
Maximum daily rainfall in South Korea 总被引：3，自引：0，他引：3
Annual maxima of daily rainfall for the years 1961–2001 are modeled for five locations in South Korea (chosen to give a good
geographical representation of the country). The generalized extreme value distribution is fitted to data from each location
to describe the extremes of rainfall and to predict its future behavior. We find evidence to suggest that the Gumbel distribution
provides the most reasonable model for four of the five locations considered. We explore the possibility of trends in the
data but find no evidence suggesting trends. We derive estimates of 10, 50, 100, 1000, 5000, 10,000, 50,000 and 100,000 year
return levels for daily rainfall and describe how they vary with the locations. This paper provides the first application
of extreme value distributions to rainfall data from South Korea. 相似文献
18.
Pham Dat T. Switzer Adam D. Huerta Gabriel Meltzner Aron J. Nguyen Huan M. Hill Emma M. 《Natural Hazards》2019,98(3):969-1001
With sea levels projected to rise as a result of climate change, it is imperative to understand not only long-term average trends, but also the spatial and temporal patterns of extreme sea level. In this study, we use a comprehensive set of 30 tide gauges spanning 1954–2014 to characterize the spatial and temporal variations of extreme sea level around the low-lying and densely populated margins of the South China Sea. We also explore the long-term evolution of extreme sea level by applying a dynamic linear model for the generalized extreme value distribution (DLM-GEV), which can be used for assessing the changes in extreme sea levels with time. Our results show that the sea-level maxima distributions range from ~?90 to 400 cm and occur seasonally across the South China Sea. In general, the sea-level maxima at northern tide gauges are approximately 25–30% higher than those in the south and are highest in summer as tropical cyclone-induced surges dominate the northern signal. In contrast, the smaller signal in the south is dominated by monsoonal winds in the winter. The trends of extreme high percentiles of sea-level values are broadly consistent with the changes in mean sea level. The DLM-GEV model characterizes the interannual variability of extreme sea level, and hence, the 50-year return levels at most tide gauges. We find small but statistically significant correlations between extreme sea level and both the Pacific Decadal Oscillation and El Niño/Southern Oscillation. Our study provides new insight into the dynamic relationships between extreme sea level, mean sea level and the tidal cycle in the South China Sea, which can contribute to preparing for coastal risks at multi-decadal timescales.
相似文献19.
覆盖层影响下典型地-井模型瞬变电磁法正演 总被引：1，自引：0，他引：1
地-井瞬变电磁法是用于地质找矿的有效方法之一,开展该方法的三维正演研究能对资料处理与解释提供帮助。在时间域有限差分算法的基础上,建立了三维地质模型和覆盖层模型,模拟了该模型下的地-井瞬变电磁响应;引入了参数EA,分析了方形低阻体和覆盖层的响应特征以及覆盖层影响因素。结果显示：低阻体位于发射场源下方时,其响应曲线呈现“双高一低”的极值特征,高峰值分别对应低阻体上下边界,低峰值对应低阻体中心;低阻体位于发射场源旁边时,其响应曲线呈现单极值特征,该特征与覆盖层响应特征相同。当覆盖层电阻率较低时,“趋肤效应”作用使覆盖层的响应强度强于低阻体;但当发射场源离钻孔足够远时,覆盖层影响可以忽略,低阻体响应强度更与覆盖层-低阻体电阻率的比值有关。孔中发射能有效降低覆盖层影响。 相似文献
20.
确定地下管线深度的方法原理研究 总被引：1，自引：0，他引：1
从理论上阐述了利用倾斜磁场最大值点、利用垂直磁场分量峰值点和利用水平磁场分量半极值点确定地下管线深度的原理方法,指出了利用倾斜磁场最大值点确定管线深度时在原理上存在的问题和不实用性,同时从原理上和实用中筛选出了最佳的定深方法-水平磁场分量三角法. 相似文献