Multivariate statistical analysis of underground gas storage caverns on groundwater chemistry in Korea

An understanding of groundwater flow and chemistry is important to operate underground storage caverns. Groundwater flow is mainly affected by cavern operating conditions. Groundwater chemistry is modified by disinfection activities for removing possible biological clogging and by mixing with cement pore water. It is important to discern these two effects, because wells affected by the disinfection activities may have hydrological connections with water curtains used to inject the disinfectant. However, it is difficult to separate these two effects using graphical methods because of their similar chemical characteristics. Instead, multivariate statistical analysis, such as principal component analysis (PCA) and factor analysis (FA), can be used. Groundwater samples for chemical analysis were obtained from four surveys in 1999–2000. Based on the results from PCA and FA, it appears that there were temporal variations of seepage water into the propane area when the cavern operation fluctuated, but we could not observe such variation in the butane area. These changes may occur mainly at depth, where water flow is slow and water renewal in the cavern surrounding is limited. Copyright © 2008 John Wiley & Sons, Ltd.     

Annealing algorithms in computing stress tensors: A set of numerical simulations for local stress tensor recovery

The determination of a local lithospheric stress pattern from low magnitude seismic activity recorded at a loca array is attempted by means of numerical simulations that include waveform inversion and annealing inversion techniques. A set of flat stratified layers are assumed for the propagating medium. The tests show that the annealing algorithm is a useful tool in this kind of study where collected seismic activity at local arrays could help us better understand local stress distributions in the lithosphere. Although real data recorded at local seismic arrays should be processed, assuming more realistic crust and upper mantle models, many characteristics of the annealing process described here could be used when studying real problems.     

Seismicity induced by gas production: II. Lithology correlated events,induced stresses and deformation

A 3D relocation technique permits precise locations of induced earthquakes. Geostatistical processing using the data of 87 boreholes provides the basis of a precise 3D structure, with a dome geometry. Conventional laboratory mechanical tests performed on deep rock samples (1000 m to 5000 m) define the rock properties at depths similar to those of the seismic events (1<M _L<4.2) that range from 1 to 7 km.In the studied period, most (85%), of the events were located above the gas reservoir, with very few located in the reservoir itself. Because the production parameters (50 MPa depletion of the gas pressure reservoir) are homogeneous throughout the gas field, the lateral inhomogeneity of the seismic rupture locations are a consequence of variations in the rheological response of the dome to the deformation induced by gas production.Here a ratio of two is found between the elastic modulus of the seismic rock matrix and the elastic modulus of the aseismic rock matrix. The contrast in strength is at least as great, if not greater. Repeated measured surface deformations involve the whole structure. Spatial and temporal deformations indicate that aseismic deformation is quantitatively the main process of this structural deformation. The heterogeneous stress pattern inferred fromP-axes of induced earthquakes disagrees with the tectonic regional stress field. The radial distribution ofP-axes towards the gas reservoir probably reflects the production induced deformation. The inferred deformation of the dome occurs in response to weak induced stresses.     

西藏尼洋河水环境特征多元统计分析

自2008年11月到2009年10月按照月份监测西藏林芝地区尼洋河水环境特征.结果显示,根据Pearson相关性矩阵,可将尼洋河26项理化指标分为3大类,分别是低度相关性理化指标、中度相关性理化指标和高度相关性理化因子.析因分析显示,可将26项理化指标分为4大类,第1类为尼洋河水体常规的理化指标、第2类为尼洋河水体硬度相关指标、第3类为海拔及第4类为影响水生生物生长的水质理化指标.PCA分析发现,平水期、丰水期以及枯水期水环境特征明显不同,以上3期各自聚为一类,而尼洋河沿程方面,水环境特征则不存在差异.构建了尼洋河海拔、底层水温与相关理化因子的一元回归方程.建议加强对尼洋河水环境的监测工作,积极推进尼洋河水域生态环境的可持续发展进程.     

形变洞室覆盖层影响垂直摆倾斜仪内在质量精度分析

统计2008-2011年全国干扰不明显的垂直摆仪器资料,分析覆盖层的厚度、岩性对仪器精度的影响以及土建成本,结果表明,并非覆盖层越厚仪器精度越高,在岩性好的地区,覆盖层无需达到40 m厚度,可节约成本,且前兆台网布局更加合理.     

Multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system

The study of groundwater hydrogeochemistry of the Paleozoic Basses-Laurentides sedimentary rock aquifer system in Québec produced a large geochemical dataset. Groundwater samples were collected at 153 sites over a 1500 km² study area and analyzed for major and minor ions. The large number of data can lead to difficulties in the integration, interpretation and representation of the results. Two multivariate statistical methods, hierarchical cluster analysis (HCA) and principal components analysis (PCA), were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples, and to identify geochemical processes controlling groundwater geochemistry. This subgroup consisted of 144 samples and 14 parameters (Ca²⁺, Mg²⁺, Na⁺, K⁺, , Cl⁻, , Fe²⁺, Mn²⁺, Br⁻, Sr²⁺, F⁻, Ba²⁺, HS⁻). Seven geochemically distinct clusters, C1–C7, resulted from the HCA. Samples from clusters C3, C4, C6 and C7 are mostly located in preferential recharge areas. The majority of these samples have Ca–Mg–HCO₃ recharge groundwater (C3, C6, C7) and Na–HCO₃ evolved groundwater (C4). Samples from the other three clusters (C1, C2, C5) are characteristic of an aquifer system under confined conditions. The majority of these samples have Na–HCO₃ evolved groundwater (C1, C5) and Na–Cl ancient groundwater that exhibits elevated concentrations in Br⁻ (C2). In addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry, the distribution of clusters also showed the importance of the geological formations on minor and trace elements, such as Fe²⁺, Mn²⁺, Sr²⁺, F⁻ and Ba²⁺. The first five components of the PCA account for 78.3% of the total variance in the dataset. Component 1 is defined by highly positive loadings in Na⁺, Cl⁻ and Br⁻ and is related to groundwater mixing with Champlain Sea water and solute diffusion from the marine clay aquitard. The high positive loadings in Ca²⁺ and Mg²⁺ of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system. From their characteristic loadings, the first two components are defined as the “salinity” and “hardness” components, respectively. Components 3–5 are related to more local and geological effects. The integration of the HCA and the PCA, with conventional classification of groundwater types, as well as with the hydrogeological and geological contexts, allowed the division of the region into four main geochemical areas, providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater. The following factors were recognized as influencing the evolution of groundwater identified in every geochemical area: (1) geological characteristics including sedimentary rock type and till mineralogy; (2) hydrogeological characteristics represented by the level of confinement and the hydraulic gradient; and (3) the geological history including the latest glaciation and the Champlain Sea invasion. With its integrated approach, this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems, and provides an example of the long-term geochemical evolution of hydrogeological systems after a major perturbation, in this case seawater invasion.     

Multivariate statistical analysis to identify the major factors governing groundwater quality in the coastal area of Kimje,South Korea

The main purpose of this study is to identify the major factors affecting groundwater quality by means of multivariate statistical analysis of the physico‐chemical compositions. Cluster analysis results show that the groundwater in the study area is classified into four groups (A, B, C and D), and factor analysis indicates that groundwater composition, 81·9% of the total variance of 17 variables, is mainly affected by three factors: seawater intrusion, microbial activity and chemical fertilizers. These results might be related to the geographical characteristics of the study area. The main influence on groundwater in groups B, C and D, which are close to the Yellow Sea and contain reclaimed areas, is the seawater intrusion by the present seawater, the trapped seawater, and microbial activity. Group A, however, has been used for agriculture for a long time, and thus groundwater in this group has been largely affected by chemical fertilizers. As groundwater flows from group A to group D according to its path, the governing factor of the groundwater quality gradually changes from chemical fertilizers to microbial activity and seawater intrusion. Copyright © 2004 John Wiley & Sons, Ltd.     

基于VAP卫星的等离子体层顶电子密度波动统计分析

基于范艾伦辐射带探测卫星的观测数据（2012年9月至2015年11月）,收集了584个等离子体层顶密度波动事件,研究了这些事件分布随磁地方时、磁壳值以及地磁活动的变化关系,并使用快速傅里叶变换分析了全部事件平均功率谱.统计结果表明,等离子体层顶密度波动事件主要发生在磁地方时黄昏扇区,其分布与磁地方时和地磁活动具有明显的相关性.等离子体层顶密度波动在1~100 mHz区间内具有接近-5/3的功率谱斜率,表明存在二维磁流体动力学湍流.本文统计结果将有助于进一步深入理解等离子体层顶密度波动在内磁层中能量传输的具体作用,并且将促进对等离子体层顶波动的激发、增强与传播过程的进一步研究.

     

Geodetic deformation vs. seismic strain deduced by historical earthquakes across the Alborz Mountains

Historical seismicity is used in order to map spatial distribution of seismic moment released by past earthquakes and to compare strain rate deduced from seismicity to those measured by geodetic GPS survey. Spatial analyses are performed on the seismicity of northern boundary of Central Iranian Block which coincides with the Alborz Mountains. This belt has been responsible for several catastrophic earthquakes in the past. In this study, the records of historical and instrumental earthquakes in the Alborz Mountains are used to calculate and plot geographical distribution of seismic moment released in time. A two-dimensional distribution function is proposed and used here to spread seismic moment along causative tectonic features. Using accumulated seismic moment, average slip rates across active faults are estimated for 32 sub-zones along the Alborz Mountains and western Kopet Dag. Seismic moment released by historical and recent earthquakes on this belt accounts for slip rate of 3–5 mm/year which is in good agreement with the geodetic vectors recently deduced from GPS survey in this region. The study also reveals geographical variations of slip rates along some 900 km length of this zone based on seismic history. The results are compared against finding from similar study in this region. Portions of Central and Eastern Alborz show lower seismic strain rate which could imply aseismic motion or overdue earthquakes. Completeness of historical earthquake catalogue and its reliability with regard to earthquake magnitudes, locations, and rupturing systems are among many plausible factors controlling the credibility of such results. Therefore, any conclusions derived from these results remain as reliable as the data and assumptions used for the analyses.     

Comparative analysis of lake plankton structure vs. function

: Four modeling approaches were used to describe variations in the plankton of a large lake. The objective was to determine whether information about ecological transfer efficiency could be predicted from metrics related to particle size, taxonomic composition, and food web structure. No relationships were found between the structural metrics and ratios of zooplankton to algal carbon uptake (one index of transfer efficiency). Ratios of zooplankton to algal biomass (another often-used index) increased significantly with food web complexity, zooplankton size, and percent dominance by Daphnia. Biomass ratios decreased with increasing algal cell size. The results provide insight into how structural properties of plankton may relate to community function.     

Improved statistical prediction of surface currents based on historic HF-radar observations

Accurate short-term prediction of surface currents can improve the efficiency of search-and-rescue operations, oil-spill response, and marine operations. We developed a linear statistical model for predicting surface currents (up to 48?h in the future) based on a short time history of past HF-radar observations (past 48?h) and an optional forecast of surface winds. Our model used empirical orthogonal functions (EOFs) to capture spatial correlations in the HF-radar data and used a linear autoregression model to predict the temporal dynamics of the EOF coefficients. We tested the developed statistical model using historical observations of surface currents in Monterey Bay, California. The predicted particle trajectories separated from particles advected with HF-radar data at a rate of 4.4?km/day. The developed model was more accurate than an existing statistical model (drifter separation of 5.5?km/day) and a circulation model (drifter separation of 8.9?km/day). When the wind forecast was not available, the accuracy of our model degraded slightly (drifter separation of 4.9?km/day), but was still better than existing models. We found that the minimal length of the HF-radar data required to train an accurate statistical model was between 1 and 2?years, depending on the accuracy desired. Our evaluation showed that the developed model is accurate, is easier to implement and maintain than existing statistical and circulation models, and can be relocated to other coastal systems of similar complexity that have a sufficient history of HF-radar observations.     

江苏省断层形变台站水准观测数据质量评价

观测数据质量受到诸多因素影响,为判断更改测量频率是否会对数据质量造成影响,选取江苏省4个断层形变台站水准观测场地不同观测频率下短水准测量数据,采用几种常用数据质量评价方法进行分析,结果表明,更改测量频率不会对水准数据观测质量与映震效能产生实质性影响。     

基于Van Allen Probes EMFISIS波动仪器观测的内磁层下频带哨声合声波全球分布的统计分析

基于Van Allen Probes近三年的EMFISIS仪器波动观测数据,对内磁层下频带哨声模合声波幅度的全球分布特性对地磁活动水平的依赖性进行了详细的统计分析,着重研究下频带合声波平均场强幅度随磁壳值L、磁地方时、地磁纬度的分布特征及不同强度区间的合声波的发生概率.结果表明,下频带合声波的波动强度与地磁活动密切正相关,处于强磁扰期间的合声波具有更大的振幅,其发生率与地磁活动强度具有同样的正相关特性.下频带合声波主要发生于午夜至下午的磁地方时区间,其余的磁地方时时段下频带合声波较弱.赤道面附近的下频带合声波主要分布在夜侧至黎明这一时段内,随着磁纬度的增加逐步向日侧扩展.下频带合声波在午夜侧（21-03 MLT）主要出现在15°的磁纬范围内,在晨侧（03-09 MLT）可以到达15°磁纬甚至更高纬度.下频带合声波主要发生于L=~4.5的附近区域.随着地磁活动的增加,下频带合声波所覆盖的L-shell空间区域增大,趋势为向高、低L值区域同时扩展.建立的下频带哨声合声波的全球分布模型将有助于进一步深入理解该重要磁层波动对辐射带电子的波粒作用散射效应和对辐射带动力学过程的定量贡献.

     

基于Van Allen Probes EMFISIS波动仪器观测的内磁层上频带哨声合声波全球分布的统计分析

基于Van Allen Probes近三年的EMFISIS仪器波动观测数据,针对内磁层上频带哨声模合声波幅度的全球分布特性对地磁活动水平的依赖性进行了详细的统计分析,着重研究上频带合声波平均场强幅度随磁壳值（L）、磁地方时（MLT）、地磁纬度（MLAT）的分布特征及不同强度区间的合声波的发生概率.结果表明,上频带合声波的平均场强幅度与地磁活动条件密切相关,在强磁扰期,平均幅度可达到40 pT以上.在外辐射带中心区域（L=4~6）,上频带合声波的幅度最强;在L＜~3的区域,上频带磁层合声波没有分布.在夜侧至晨侧（22-09MLT）,上频带合声波幅度最强;在下午侧至昏侧（15-19MLT）,上频带合声波幅度最弱;日侧（10-14MLT）上频带合声波在不同地磁活动条件下都存在,幅度偏小.上频带合声波主要分布在|MLAT| < 10°,其中21-09MLT范围内、磁纬位于|MLAT| < 5°的平均场强幅度最强,磁扰期间可达约100 pT.另外,统计而言,中等幅度（10~30 pT）的上频带合声波在夜侧至晨侧（23-09MLT）靠近磁赤道区域的发生率最高,可达15%左右.强幅度（>30 pT）的上频带合声波普遍分布在夜侧（01-05MLT）,发生率最小.本文建立的上频带哨声模合声波的全球分布模型结合已经建立的下频带合声波的全球分布模型,将有助于进一步深入理解该重要磁层等离子体波动对地球等离子体片、辐射带、环电流动力学过程的定量贡献.

     

Rainfall-triggered ordinary earthquakes in Taiwan: a statistical analysis

Abstract

This study was carried out to investigate the role of rainfall in triggering ordinary earthquakes that occurred before and after the major Chi-Chi earthquake (7.2 M_L) in central Taiwan on 21 September 1999. To test a possible mechanism, earthquake activities from January 1995 to July 2012 were examined. The Chi-square (χ²) test revealed a significant difference between the correlations of monthly accumulated rainfall values and earthquake activities before and after the Chi-Chi earthquake. This result is discussed in terms of changes in crustal conditions after the Chi-Chi earthquake. Two ordinary earthquakes that may have been associated with heavy rainfall after the Chi-Chi earthquake are identified.

Editor D. Koutsoyiannis; Associate editor A. Porporato

Citation Lin, J.-W., 2014. Rainfall-triggered ordinary earthquakes in Taiwan: a statistical analysis. Hydrological Sciences Journal, 59 (5), 1074–1080.     

基于独立分量分析的多次波自适应相减技术

针对多次波自适应相减这个关键问题,文中首次提出利用独立分量分析技术来实现多次波和一次波的分离（简称ICAAMS）. 现有的多次波自适应相减技术大都是采用输出信号（一次波）能量最小准则,基于二阶统计量的技术. 本文提出的ICAAMS采用了输出信号非高斯性最大准则,并利用高阶统计量来表征非高斯性. 简单的褶积模型和复杂的有限差分模型资料处理结果表明, 本文提出的方法可以有效地分离一次波和多次波.     

Scale-based statistical analysis of sediment fluxes

The flux of sediments over a line perpendicular to the main flow direction was measured during experiments of weak one-dimensional bed load. The standard definition of solid discharge through a boundary is a straightforward issue, yet the dependence of resulting values on the spatial and temporal scales used as a support for measurement is not. In this work, first- and second-order statistics of sediment transport rates were analyzed as scale-dependent quantities. The spatial scales used were significantly larger than the particle size, while the temporal scales covered a two-orders-of-magnitude range enabling the physical time scales of the single particles to be appreciated. In addition, the relationship between sediment fluxes, process intermittency and particle interarrival times was investigated. Proper knowledge of the scale-dependence of statistical properties of sediment transport fluxes may allow for adequate design of measuring campaigns (both in the laboratory and field) and for sound interpretation of data from multiple sources.     

乌加河地震台形变观测异常与干扰识别

收集并整理2018—2020年乌加河中心地震台VP型垂直摆、体应变仪、伸缩仪和水管倾斜仪等形变观测资料,分析归纳地球物理异常与各类干扰特征,自然因素、人为干扰和地球物理事件在观测曲线上主要表现为噪声大、阶跃、台阶、突跳、高频干扰和趋势性变化、同震响应等特征。不同观测仪器对各类干扰的响应不同,甄别并分析干扰特征及原因,可为准确识别各类形变干扰提供依据。     

Time vs. Money: A Quantitative Evaluation of Monitoring Frequency vs. Monitoring Duration

The National Research Council has estimated that over 126,000 contaminated groundwater sites are unlikely to achieve low ug/L clean‐up goals in the foreseeable future. At these sites, cost‐effective, long‐term monitoring schemes are needed in order to understand the long‐term changes in contaminant concentrations. Current monitoring optimization schemes rely on site‐specific evaluations to optimize groundwater monitoring frequency. However, when using linear regression to estimate the long‐term zero‐order or first‐order contaminant attenuation rate, the effect of monitoring frequency and monitoring duration on the accuracy and confidence for the estimated attenuation rate is not site‐specific. For a fixed number of monitoring events, doubling the time between monitoring events (e.g., changing from quarterly monitoring to semi‐annual monitoring) will double the accuracy of estimated attenuation rate. For a fixed monitoring frequency (e.g., semi‐annual monitoring), increasing the number of monitoring events by 60% will double the accuracy of the estimated attenuation rate. Combining these two factors, doubling the time between monitoring events (e.g., quarterly monitoring to semi‐annual monitoring) while decreasing the total number of monitoring events by 38% will result in no change in the accuracy of the estimated attenuation rate. However, the time required to collect this dataset will increase by 25%. Understanding that the trade‐off between monitoring frequency and monitoring duration is not site‐specific should simplify the process of optimizing groundwater monitoring frequency at contaminated groundwater sites.