A Spatial Point Process Model for Violent Tornado Occurrence in the US Great Plains

The authors illustrate a statistical point process model that uses the spatial occurrence of nonviolent tornadoes to predict the distribution of the rare, violent tornadoes that occur during springtime across the US central Great Plains. The average rate of nonviolent tornadoes is 55 per 10⁴ km² per 62 years which compares with an average rate of only 1.5 violent tornadoes per 10⁴ km² over the same period (less than 3 %). Violent tornado report density peaks at 2.6 per 10⁴ km² (62 yr) in the city but is only 0.7 per 10⁴ km² in the countryside. The risk of a violent tornado is higher by a factor of 1.5, on average, in the vicinity of less violent tornadoes after accounting for the population bias. The model for the occurrence rate of violent tornadoes indicates that rates are lower by 10.3 (3.6, 16.5) % (95 % CI) for every 1 km increase in distance from the nearest nonviolent tornado, controlling for distance from the nearest city. Model significance and the distance-from-nearest nonviolent tornado parameter are not sensitive to population threshold or the definition of a violent tornado. The authors show that the model is useful for generating a catalogue of touchdown points that can be used as a component to a tornado catastrophe model.     

Sampling Bias and Class Imbalance in Maximum-likelihood Logistic Regression

Logistic regression is a widely used statistical method to relate a binary response variable to a set of explanatory variables and maximum likelihood is the most commonly used method for parameter estimation. A maximum-likelihood logistic regression (MLLR) model predicts the probability of the event from binary data defining the event. Currently, MLLR models are used in a myriad of fields including geosciences, natural hazard evaluation, medical diagnosis, homeland security, finance, and many others. In such applications, the empirical sample data often exhibit class imbalance, where one class is represented by a large number of events while the other is represented by only a few. In addition, the data also exhibit sampling bias, which occurs when there is a difference between the class distribution in the sample compared to the actual class distribution in the population. Previous studies have evaluated how class imbalance and sampling bias affect the predictive capability of asymptotic classification algorithms such as MLLR, yet no definitive conclusions have been reached.     

松辽盆地西斜坡上白垩统青山口组二段及三段底部四级层序格架下沉积微相分布

综合利用地震、录井、测井、岩心资料,建立了松辽盆地西斜坡上白垩统青山口组二段及三段底部四级层序地层格架,查明了四级层序格架内沉积微相的空间分布。青山口组二段划分为2个四级层序(Cg4、Cg3),每个四级层序均可划分为湖泊扩张体系域和湖泊收缩体系域,分别命名为Eg4、Sg4,Eg3、Sg3。西斜坡青山口组二段及三段底部的沉积格局为滨浅湖沉积体(砂坝、泥滩、混合滩)和三角洲前缘沉积体(河口坝、远砂坝)共存。Eg4沉积时期发育了物源来自西部与北部的4个三角洲前缘沉积体,沉积体之间发育滨浅湖混合滩;Sg4沉积时期三角洲沉积体规模较前期扩大,并且发育了物源来自西北方向的三角洲。Eg3沉积时期物源来自西部及北部的三角洲向东推进,东北部三角洲前缘沉积体萎缩;Sg3沉积时期以三角洲前缘沉积占优势,三角洲前缘沉积体错叠连片,滨浅湖沉积大量减少。青山口组二段及三段底部自下而上,沉积区范围和三角洲前缘沉积体的规模逐渐扩大。     

Phytolith analysis from the archaeological site of Kush, Ras al-Khaimah, United Arab Emirates

Despite the wealth of archaeological sites and excellent conditions for preservation, few phytolith investigations have been undertaken from the Arabian Gulf region. The results from the Sasanian and Islamic archaeological tell of Kush, Ras al-Khaimah, United Arab Emirates, are presented. Kush is situated just inside the Gulf on an important trade route. The occupation sequence dates from the 4^th century A.D. until the 13^th century A.D., recording the development of the site in the Sasanian period, followed by the arrival of Islam in the 7^th century A.D. and the final abandonment of the site in the late 13^th century when the nearby site of al-Mataf (Julfar) began to develop closer to the present day coastline. All the samples analyzed contained abundant phytoliths (short cells, elongated cells, and groups of elongated cells) of various types. They included date palm (Phoenix dactylifera), papillae (possibly from barley (Hordeum)), and hair cells possibly from species of canary grass (Phalaris spp.). Some researchers have suggested that groups of elongated cells may indicate the presence of irrigation in semiarid environments. The present results for this class of phytoliths appeared to imply that intensive irrigation was unlikely to have taken place around Kush.     

Lognormality in the observed size distribution of oil and gas pools as a consequence of sampling bias

Economic filtration has been offered as an explanation of the observed lognormality in the size distribution of discovered oil and gas deposits. The result leads to the conclusion that one cannot impute the shape of the underlying parent distribution from the observed discoveries size distribution. The fact that the largest pools tend to be discovered early in the exploration history of an area of interest suggests the existence of an inherent sampling bias in the discovery process. The bias is influenced by the levels of geologic knowledge and technological sophistication. Furthermore, the existence of the bias leads to lognormality in the observed discoveries size distribution of oil and gas pools. A discovery process model explicitly incorporating the notion of sampling bias was applied to a series of Weibull parent frequency size distributions. The selected parent distributions are of a class suggested in the literature as more reflective of nature's size distribution and have empirical support. The distribution of discoveries resulting from the application of the model to the chosen parent size distributions were tested for lognormality using a chi-squared test. Lognormality was found to be an acceptable model of the discoveries size distribution over a wide range of resource exhaustion measures. When combined with the notion of economic filtration, sampling bias leads to the conclusion that one should not expect the lognormal distribution to accurately represent the underlying parent size distribution of oil and gas deposits.     

Occurrence and distribution of fluoride in the groundwater of the Tamiraparani River basin,South India: a geostatistical modeling approach

Fluoride in drinking water has both beneficial and detrimental effects on public health, and a narrow range between .6 and 1.5 mg/L is optimal for consumption. However, natural groundwater sources exceed these guidelines affecting the entire population. This study aims to assess the distribution and controlling factors of fluoride concentration in the Tamiraparani River basin, South India. A total of 124 groundwater samples were analyzed for their fluoride content and other hydrogeochemical parameters. The fluoride concentration in the study area varied from .01 to 1.67 mg/L, and the highest concentrations were measured in the northern and central parts of the study area, which is underlain by charnockites and hornblende biotite gneiss. The sampling indicated (as per the Bureau of Indian Standards) that 53.9% of the area has fluoride concentrations below levels that are protective of teeth from dental caries (<.6 mg/L). .1% of the area is considered to be at risk of dental fluorosis, and the remaining 46% of the area is considered to have fluoride levels at desirable to permissible limit in groundwater. The groundwater in the study area belongs to Ca–Mg–Cl–SO₄ and Ca–Mg–HCO₃ types. A positive correlation between fluoride and TDS, Na⁺, K⁺ and HCO₃ ^? indicates its geogenic origin, and positive loading between pH and fluoride shows that alkaline environment enhances the dissolution of fluoride-bearing minerals into the groundwater. An empirical Bayesian kriging model was applied to interpolate the fluoride concentration in the study area. This geostatistical model is found to be better than other kriging methods, and it yielded an average standard error of .332 and root-mean-square standardized value of .986.     

近千年来中国气温模拟与重建资料的对比分析

依据伞球海气耦合气候模式ECHO-G近千年积分模拟结果,通过对中国气温模拟序列与重建资料进行对比分析,以验证模式对中国地区气温变化的模拟能力.结果表明模拟结果与重建资料都明显体现出了11世纪至14世纪的中世纪暖期、15世纪至19世纪的小冰期及20世纪的现代暖期3个气候特征时期,并且二者在冷暖时期的转换时间上也较吻合,模...     

Spatial distribution of groundwater quality parameters in the Velika Morava River Basin,central Serbia

The reported study includes analysis of 14 physico-chemical parameters of alluvial groundwater based on data collected from 26 piezometers in the Velika Morava River Basin from 2004 to 2014. Eleven of the parameters were assessed applying hierarchical cluster analysis and principal component analysis to examine the spatial distribution, identify the main processes in groundwater variations and segregate the dominant sampling sites based on the characteristic parameters. A Piper diagram shows that the studied alluvial groundwaters are predominantly of the Ca²⁺–HCO₃^? type (67.3%) and to a lesser extent of the mixed Ca²⁺–Mg²⁺–HCO₃^? type (21.6%). Hierarchical clustering results in four clusters depending on the similarities of the hydrochemical parameters. Principal component analysis explains 65.4% of total variance with PC1 (32.5% variance), PC2 (19.8% variance) and PC3 (13.1% variance). A comparative analysis reveals that the main processes responsible for the hydrochemical composition of groundwater in the Velika Morava alluvion are carbonate dissolution-anthropogenic pressure, feldspar weathering and migration caused by river–aquifer interaction. Considerable loading of the alluvial groundwater caused by a complex geologic framework, natural factors and human activities in the river basin contributed to the segregation of six dominant sampling sites. The obtained results can be very useful in the development of an optimal spatial plan for groundwater monitoring, focusing on increasing the density of the national monitoring network and frequency of assessing alluvial groundwater on the dominant sampling sites (from annual to seasonal).     

Estimation on organic carbon content of source rocks by logging evaluation method as exemplified by those of the 4th and 3rd members of the Shahejie Formation in western sag of the Liaohe Oilfield

One of the most important tasks of evaluating natural resources of petroliferous basins is to determine the organic matter abundance of source rocks in the basin.The usual method for assessing the organic carbon content of source rocks is based on laboratory analyses.There is a deviation in calculating organic carbon content due to the heterogeneous distribution of organic matter and the artificial factors when sampling.According to the continuous characteristics of information logging,the conventional logging curves(mainly acoustics and resistivity,etc.) were calibrated with the organic carbon experimental data of cores,cuttings or sidewall cores.The organic carbon content of source rocks of the 4 th(Es 4) and 3 rd(Es 3) members of the Shahejie Formation in western sag in the Liaohe depression was estimated directly by a great amount of continuous data including resistivity and acoustic logging,etc.Comparison between the results from computer processing and lab analysis of logging data shows that the organic carbon contents derived from the computer processing of logging data have the same reliability and accuracy as the lab analysis results.The present data show that this method is suitable to evaluate the source rocks of western sag in the Liaohe depression and has great potential in evaluating natural resources of sedimentary basins in the future.On the basis of logging data of source rocks,experimental data and existing geochemical analyses of the Liaohe Oilfield,the corresponding total organic carbon(TOC) isograms of source rocks were plotted.The source rocks of Es 4 and Es 3 of the Shahejie Formation are thought to be beneficial to hydrocarbon accumulation due to the high TOC.     

Discrimination of explosions and earthquakes: An example based on spectra and source parameters of the 11<Superscript>th</Superscript> May 1998 Pokhran explosion and the 9<Superscript>th</Superscript> April 2009 earthquake

We compare the P-, S- and Lg- spectra of the 11^th May, 1998 Pokhran underground nuclear explosion (NE) with those of an earthquake (EQ) of comparable magnitude that occurred in its vicinity (~100 km west) on 9^th April, 2009, utilizing the waveforms recorded by a Global Seismograph Network station at Nilore (NIL), Pakistan. The contiguous occurrence of these events and the similarity of the travel paths provided a good opportunity to discriminate the nature of the sources. Our results suggest that the Pn/Lg and Pn/Sn amplitude ratios of the explosion and earthquake waveforms exhibit distinct differences in the higher frequency window. Further, since the P-phases have high signal to noise ratio compared to their S counterparts, we utilize their spectra to derive the source parameters of the NE and EQ sources. Our results show that the seismic moment, corner frequency and source dimension of the explosion are ~1.58X10¹⁷ Nm, 1.18 Hz and ~0.793 km respectively. The moment magnitude (M_W) and surface wave magnitude (M_S) for the nuclear explosion are estimated to be ~5.4 and ~3.57 respectively. The values of M_W (5.3) and M_S (4.3) obtained by us for the earthquake are consistent with the estimates in the Harvard catalog and earlier published results. The estimate of M_W for the nuclear explosion was hitherto not available. Lastly, we estimate the yield of the NE to be ~50 kt from the surface wave magnitude and discuss the various limitations related to its estimation.     

Radionuclide migration at experimental polygon at Red Forest waste site in Chernobyl zone. Part 2: Hydrogeological characterization and groundwater transport modeling

This article represents the second of two articles, which review the main results of the international radioecological projects: Chernobyl Pilot Site Project (1999–2003) and Experimental Platform in Chernobyl (2004–2008). These projects studied radionuclide migration from the near-surface radioactive waste trench at the Red Forest waste dump in the Chernobyl zone, which contained nuclear fuel particles. This article presents results from the comprehensive hydrogeological site characterization program including the following issues: geological structure of the study site, hydraulic properties of the deposits, tracer tests in the aquifer, results of groundwater monitoring and unsaturated zone regime studies, as well as data on the ⁹⁰Sr distribution in the unsaturated zone and aquifer, and analyses of ⁹⁰Sr sorption behavior. The derived parameters were used to develop and calibrate 1D (flow tube) and 2D (cross-section) models describing the migration of ⁹⁰Sr from the studied waste trench to the unsaturated zone and aquifer over a 16-a period (1986–2002). The models involved the following sub-models: (1) the geostatistical (structural) model for radioactivity distribution in the trench (using GSLIB); and (2) the radionuclide source term model (STERM1D) describing dissolution of fuel particles and a 1D of radionuclide redistribution in the trench body and unsaturated zone. The MODFLOW – MT3D codes were used to model the 2D ⁹⁰Sr transport in the aquifer cross-section. Calibration of the 1D model with respect to K_ds and dispersivities allowed quite accurate reproduction of ⁹⁰Sr migration behavior for the early period (1995–1998). The less perfect fit between the 1D and 2D modeling results and monitoring data for the later period (1999–2002) suggests the need to improve the conceptual radionuclide migration model (i.e. to account for transient hydraulic and geochemical regimes of the waste site).     

青藏高原北缘哈拉湖近800年来 湖泊沉积及其环境意义*

文章以青藏高原北缘高山祁连山湖泊——哈拉湖作为研究对象,利用放射性核素²¹⁰ Pb和¹³⁷ Cs测年资料,通过对此高海拔湖泊沉积碳酸盐氧碳同位素、碳酸盐含量、总有机碳含量、磁化率等环境代用指标的分析,揭示了这一地区近800年来的气候环境变化过程。分析表明哈拉湖记录的气候环境变化经历了3个阶段:1206~1700A.D.环境较为寒冷、湿润,并有持续变湿的趋势;1700~1920A.D.环境由冷湿的状况趋向温暖干旱,1771年之后,环境保持相对稳定;1920~2002A.D.是自1206年以来最为温暖干旱的阶段。     

Hatching,estuarine transport,and distribution of larval and early juvenile Atlantic tomcod,Microgadus tomcod,in the Hudson River

Atlantic tomcod larvae, hatching in late February and early March 1975 and 1976 into a regime of accelerating river flows, were moved rapidly downriver from milepoint 42–54 (MP 0 is the estuary mouth) to the most seaward reaches of the estuary. This resulted in a spatiotemporal distribution markedly different from that of other Hudson River fish species. Peak tomcod density on posthatch sampling dates was observed most frequently at the George Washington Bridge station (MP 11). Correlation between movements of the 1.0‰ salt front and movements of the age-0 tomcod population was high (r=0.82); and may have been enhanced by high freshwater flows. The population epicenter was always seaward of the 1.0‰ salt front and mean distance between the two was 16–17 km. Moved by tidal and freshwater flows, the tomcod population oscillated between MP 0 and MP 43 during March–May 1973–1976. Location of the population epicenter after mid march was predicted (r²=0.76) to be seaward of the Tappan Zee Bridge (MP 30) when freshwater flows were greater than 450 m³ s^?1. During flow regimes greater than 1,290 m³ s^?1, the epicenter was predicted to be seaward of the George Washington Bridge (MP 11). An optimum-allocation sampling design for age-0 tomcod showed that 58% of the total effort from mid March to early June should be directed to the river region between MP 0 and MP 24, a region largely ignored in previous studies. *** DIRECT SUPPORT *** A01BY066 00013     

A Methodology for Predicting the In Situ Size and Shape Distribution of Rock Blocks

Summary In block caving, it is important to estimate the cavability of an ore body. This study proposes a new three dimensional (3D) model for predicting the characteristics of ore fragmentation in block caving, which is based on the Monte Carlo simulation technique. In this paper, the following subjects are discussed: sampling methods of discontinuity, 3D modeling algorithms and conceptualization for analyzing the distribution of discontinuities. In addition, the influence of each modeling parameter on the distribution of ore fragmentation was analyzed. The characteristics of ore fragmentation in a Northern China underground copper mine are used as a case study. Based on the methods discussed here, a software system named “MAKEBLOCK” was developed for analyzing the characteristics of discontinuities in an ore body and predicting the size distribution of ore fragments in block caving. The ore fragmentation attained by using this 3D model is in a good agreement with the field fragmentation measurements. Received November 30, 2001; accepted September 19, 2002; Published online February 25, 2003 Acknowledgement Support for this project came primarily from The National Science Foundation of China (approval No. 59704004). We would like to thank professor J. F. Archbald, head of Faculty of Mining Engineering, Queen's University, Canada, for his excellent advice and for checking the technical presentations of this paper. Authors' address: Dr. Liguan Wang, College of Resources and Safety Engineering, Central South University, Hunan, Changsha, China; e-mail: liguan_wang@hotmail.com     

Isovolumetric geochemical investigation of a buried granite saprolite near Columbia,SC, U.S.A.

Saprolites are residual soils which preserve the textures of their parent rocks and thus have evolved by an isovolumetric process of weathering (MILLOT, 1970, The Geology of Clays, Springer). Using bulk density, saprolite elemental analyses can be converted to units of g cm^?3. Furthermore, an empirical reaction progress diagram can be constructed for a suite of saprolite samples by plotting element concentrations (in g cm^?3) against bulk density (B.D.). Our data for a granite saprolite show that Al₂O₃ and SiO₂ decrease in a linear fashion from B.D. 2.1g cm^?3 to 1.5g cm^?3 but that K₂O follows a curvilinear trend such that it decreases from 75% of its fresh rock value at B.D. 1.6 g cm^?3 to nearly zero at B.D. 1.5 g cm^?3. The only hypothetical reaction paths that are compatible with these B.D. vs A1₂O₃, SiO₂ and K₂O constraints are those in which orthoclase alters to kaolinite through an intermediate potassium phase similar to KAl₃Si₃O₁₀(OH)₂ or KAl₂Si₂O₆(OH)₃ (hypothetical K-kaolinite). Normative mineral calculations, X-ray diffraction data and structural H₂O data are employed to test this conclusion.     

Multidimensional statistical technique for detection of low contrast geochemical anomalies

In this article we propose an advanced technique for detecting low contrast geochemical anomalies using a set of features. There are three principal elements in this technique: (1) a statistical measure of the contrast of the anomaly, denoted as τ; (2) selection of a background population; and (3) reduction of the dimensionality of the feature space. In the frame of the model, which describes the statistical distribution of geochemical background as a multidimensional normal distribution of logarithms of concentrations, the index, τ, is a powerful test statistic for the hypothesis of abnormality of an observation. Maps of τ anomalies can be rigorously interpreted on the basis of statistical inferences. Under all equal conditions this technique allows the detection of geochemical anomalies with at least the same contrast (if the chemical elements in a background population are correlated, then even the better) as using selective extractions of metals from soil or other techniques for data processing. The advantages of the proposed technique are demonstrated both theoretically and on examples of rare-metal and copper–nickel mineral deposits.     

新疆罗布泊地区近160年来红柳沙包沉积纹层δ13C与气候重建

红柳沙包具有准确的计年和很强的环境信息储存功能,可以用来恢复数百年来的气候和环境变化。研究发现,罗布泊红柳沙包沉积纹层红柳落叶 δ13 C 序列高频变化受多个气候要素的综合影响,重建的罗布泊地区1839年以来的年平均气温、8~10月空气平均相对湿度及4~5月平均风速,较好地反映了该地区168年来的气候变化。对红柳落叶 δ13 C 高频变化序列的功率谱分析发现, δ13 C 序列含有显著的42.0a,10.5a,8.4a,4.0a,3.7a和2.9a等准变化周期,其中,准10.5a周期与太阳黑子约11.0a的活动周期基本一致。     

P-III型分布混合权函数估计法的研究

为克服传统的马秀峰权函数法所存在的缺陷,提出了一种可考虑线性矩法优点的新的权函数估计法即混合权函数法,经过统计试验论证,该法对传统的马秀峰权函数法有较大改进,是一种统计性能较优秀的参数估计方法。     

Bayesian Estimation of Earth’s Undiscovered Mineralogical Diversity Using Noninformative Priors

Recently, statistical distributions have been explored to provide estimates of the mineralogical diversity of Earth, and Earth-like planets. In this paper, a Bayesian approach is introduced to estimate Earth’s undiscovered mineralogical diversity. Samples are generated from a posterior distribution of the model parameters using Markov chain Monte Carlo simulations such that estimates and inference are directly obtained. It was previously shown that the mineral species frequency distribution conforms to a generalized inverse Gauss–Poisson (GIGP) large number of rare events model. Even though the model fit was good, the population size estimate obtained by using this model was found to be unreasonably low by mineralogists. In this paper, several zero-truncated, mixed Poisson distributions are fitted and compared, where the Poisson-lognormal distribution is found to provide the best fit. Subsequently, the population size estimates obtained by Bayesian methods are compared to the empirical Bayes estimates. Species accumulation curves are constructed and employed to estimate the population size as a function of sampling size. Finally, the relative abundances, and hence the occurrence probabilities of species in a random sample, are calculated numerically for all mineral species in Earth’s crust using the Poisson-lognormal distribution. These calculations are connected and compared to the calculations obtained in a previous paper using the GIGP model for which mineralogical criteria of an Earth-like planet were given.

     

A numerical comparison of enhancing horizontal resolution (EHR) technique utilizing 2D resistivity imaging

The effectiveness of inversion apparent resistivity data to determine accurately the true resistivity distribution over 2D structures has been investigated using a common inversion scheme based on smoothness-constrained nonlinear least-squares optimization with enhancing horizontal resolution (EHR) technique by numerical simulation. The theoretical model generates in RES2DMOD software at specific distance and depth using Wenner, Wenner–Schlumberger, and pole–dipole arrays were inverted. The inversion model was compared with the original 2D model in RES2DINV software. The study model includes horizontal layering, vertical resolution, and horizontal two layers with different resistivity. Also, the response to variations in data density of these arrays was investigated. The study shows the best array suitable to be used in the survey was chosen for real data acquisition at the actual site. Subsequently, the results from borehole were used to verify the results of 2D resistivity imaging method with and without EHR technique. Saturated zone (0–40 Ω-m) was found scattered at the depth of 10–20 m. The borehole is located at 63 m at 2D resistivity imaging survey which shows at depth 10–20 m is sandy silt. Highly weathered sandstone was found at 6 m depth with resistivity value of 800 Ω-m and SPT N value of 20. The bedrock was found at 27 m depth with resistivity value of 3,000 Ω-m and SPT N value of 50. The application of 2D resistivity imaging with EHR technique indicate the ability of the proposed approach in terms of density, depth, and resistivity value of anomalous and layer in a computationally and numerically efficient manner and to exhibit good performance in the data inversion.