Water Quality Monitoring of Tropical Ponds: Location and Depth Effect in Two Case Studies

The variability in water chemistry of samples taken on a monthly basis (March 1999 to February 2000) from two shallow tropical ponds was studied. The effect of location and pond depth on water chemistry was also examined. The study demonstrated that intraannual variability in nutrient concentration is high. Thus, a high annual sampling frequency is required to provide representative annual mean water quality data. Routine monitoring during the monsoons is important for studies on dissolved oxygen and macrophyte growth. Significant differences were found between the topmost and bottommost points for samples of dissolved oxygen collected from the deepest part of both ponds. For nutrient analysis (nitrogen and phosphorus), sample from any location was found to be representative of the whole pond.     

Cone Penetrometer Tests and HydroPunch® Sampling: A Screening Technique for Plume Definition

Cone penetrometer tests and HydroPunch® sampling were used to define the extent of volatile organic compounds in ground water. The investigation indicated that the combination of these techniques is effective for obtaining ground water samples for preliminary plume definition. HydroPunch samples can be collected in unconsolidated sediments and the analytical results obtained from these samples are comparable to those obtained from adjacent monitoring wells. This sampling method is a rapid and cost-effective screening technique for characterizing the extent of contaminant plumes in soft sediment environments. Use of this screening technique allowed monitoring wells to be located at the plume boundary, thereby reducing the number of wells installed and the overall cost of the plume definition program.     

河北应变固体潮汐参数及震例研究

选取河北省5个形变台站的观测资料,利用Venedikov调和分析法计算河北省境内M_S4.0以上的潮汐因子、相位等参数,发现应变潮汐因子对地震都有多则半年,少则几周的异常期。宽城台对河北省境内发生M_S4.0以上的地震中,震中距较其他台站最近(震中距最远为350km、最近为100km),资料较好,故在综合分析河北应变台站的基础上,重点选取宽城台的应变潮汐因子对河北2005—2015年地震案例进行简要分析,发现该台对地震的对应率达到60%,虚报率40%,漏报率极低只有14%,前兆异常可信度较高,可作为前兆异常的参考。     

Sampling Plan Optimization: A Data Review and Sampling Frequency Evaluation Process

Lawrence Livermore National Laboratory (LLNL) uses a cost-effective sampling (CES) methodology to evaluate and review ground water contaminant data and optimize the site's ground water monitoring plan. The CES methodology is part of LLNL's regulatory approved compliance monitoring plan (Lamarre et al. 1996). It allows LLNL to adjust the ground water sampling plan every quarter in response to changing conditions at the site. Since the use of the CES methodology has been approved by the appropriate regulatory agencies, such adjustments do not need additional regulatory approval. This permits LLNL to respond more quickly to changing conditions. The CES methodology bases the sampling frequency for each location on trend, variability, and magnitude statistics describing the contaminants at that location, and on the input of the technical staff (hydrologists, chemists, statisticians, and project leaders). After initial setup is complete, each application of CES takes only a few days for as many as 400 wells. Effective use of the CES methodology requires sufficient data, an understanding of contaminant transport at the site, and an adequate number of monitoring wells downgradient of the contamination. The initial implementation of CES at LLNL in 1992 produced a 40% reduction in the required number of annual routine ground water samples at LLNL. This has saved LLNL $390,000 annually in sampling, analysis, and data management costs.     

Induced Microearthquake Patterns in Hydrocarbon and Geothermal Reservoirs: Six Case Studies

—?The injection or production of fluids can induce microseismic events in hydrocarbon and geothermal reservoirs. By deploying sensors downhole, data sets have been collected that consist of a few hundred to well over 10,000 induced events. We find that most induced events cluster into well-defined geometrical patterns. In many cases, we must apply high-precision, relative location techniques to observe these patterns. At three sedimentary sites, thin horizontal strands of activity are commonly found within the location patterns. We believe this reflects fracture containment between stratigraphic layers of differing mechanical properties or states of stress. At a massive carbonate and two crystalline sites, combinations of linear and planar features indicate networks of intersecting fractures and allow us to infer positions of aseismic fractures through their influence on the location patterns. In addition, the fine-scale seismicity patterns often evolve systematically with time. At sedimentary sites, migration of seismicity toward the injection point has been observed and may result from slip-induced stress along fractures that initially have little resolved shear. In such cases, triggering events may be critical to generate high levels of seismic activity. At one crystalline site, the early occurrence of linear features that traverse planes of activity indicate permeable zones and possible flow paths within fractures. We hope the continued development of microseismic techniques and refinement of conceptual models will further increase our understanding of fluid behavior and lead to improved resource management in fractured reservoirs.     

A Case Study of Soil-Gas Sampling in Silt and Clay-Rich (Low-Permeability) Soils

Soil-gas sampling and analysis is a common tool used in vapor intrusion assessments; however, sample collection becomes more difficult in fine-grained, low-permeability soils because of limitations on the flow rate that can be sustained during purging and sampling. This affects the time required to extract sufficient volume to satisfy purging and sampling requirements. The soil-gas probe tubing or pipe and sandpack around the probe screen should generally be purged prior to sampling. After purging, additional soil gas must be extracted for chemical analysis, which may include field screening, laboratory analysis, occasional duplicate samples, or analysis for more than one analytical method (e.g., volatile organic compounds and semivolatile organic compounds). At present, most regulatory guidance documents do not distinguish between soil-gas sampling methods that are appropriate for high- or low-permeability soils. This paper discusses permeability influences on soil-gas sample collection and reports data from a case study involving soil-gas sampling from silt and clay-rich soils with moderate to extremely low gas permeability to identify a sampling approach that yields reproducible samples with data quality appropriate for vapor intrusion investigations for a wide range of gas-permeability conditions.     

Petroleum Electromagnetic Prospecting Advances and Case Studies in China

Remarkable progress has been made in electromagnetic (EM) techniques as applied to the petroleum industry in instruments, data acquisition, and processing and interpretation in China. Included here is equipment, such as high-power Controlled Source EM (CSEM) acquisition systems, acquisition methods, such as the three dimensional small-bin Continuous Electromagnetic Array acquisition method, Time and Frequency Domain Controlled Source Electromagnetic, Borehole-to-surface Electromagnetic technique and marine magnetotelluric method. Data processing methods, such as fast three dimensional inversion using nonlinear conjugate gradients, and data interpretation methods, like Induced Polarization and Resistivity anomalies for hydrocarbon detection, are also included. These new techniques have been applied in petroleum survey and many cases are in complicated areas. They have successfully served the investigation of deep igneous rock reservoirs, and prediction of potential hydrocarbon targets. The cases indicate that electromagnetic techniques can help seismic survey to effectively detect hydrocarbon reservoir and remarkably improve drilling successes.     

Geoelectromagnetic Exploration For Natural Resources: Models, Case Studies And Challenges

This paper presents a tutorial review of electrical and electromagnetic(herein collectively called geoelectromagnetic) methods as applied in the search for natural resources. First, the paper discusses the technical problems and advances in geoelectromagnetic methods in the last decade. A scheme for integrating electrical and electromagnetic depth sounding data is suggested.Then, for natural resources exploration, it focuses on three themes: (1) understandinggeological models of resource targets, their physical properties, and the development of conceptual geoelectromagnetic exploration models, (2) overview of geoelectromagnetic case studies in resourceexploration, and (3) outstanding challenges in exploration. For brevity, model development is restricted to groundwater, geothermal and hydrocarbon resources, metallic ore-bodies (exemplified byvolcanogenic massive sulphides, porphyry coppers, and epithermal and Archaean greenstone belt gold deposits) and diamonds. In the treatment of resource exploration in this paper, the unifying themeis that geochemical processes of weathering and hydrothermal alteration form clayey products that may render natural resource targets directly or indirectly detectable by their resistivity characteristics.Since hydrated clays are an important feature of most resource types and are major causes of low resistivity anomalies in geoelectromagnetic exploration, they may be taken as providing detectable marker horizons or pathfinders and a basis for developing a consistent investigative approachfor natural resources. However, it is recognised that no single resource model or standard approach may be universally applicable. Natural resource systems are inherently 3D and require large numbers of depth soundings at high station densities to image adequately. Thus, developing methodsof increasing the productivity of data acquisition, the development of better 3D software tools and lowering costs are seen as the major challenges facing the use of geoelectromagnetic methods for naturalresource exploration.     

地震科技文章初审过程中想到的两个问题

努力提高地震科技期刊的学术质量,是科技期刊编辑努力追求的目标.一个期刊所刊载文章的学术质量是科技期刊价值的体现,而学术质量又取决于它所拥有的原创文稿的价值,文稿的价值反映在学术价值、研究价值和资料价值这3个方面.文稿的学术价值即文稿在某学科领域中具有超前性、创新性:文稿的研究价值即文稿对于人们从事学术研究具有的启示性、借鉴性;文稿的资料价值即文稿对于系统了解学术研究动态具有收藏价值(许金华等,2005).     

Path Corrections for Source Discriminants: A Case Study at Two International Seismic Monitoring Stations

—?Improving the performance of short-period regional seismic discriminants by applying propagation corrections is explored using observations from two seismic monitoring stations in Asia. Frequency-dependent regional phase amplitude ratio measurements at stations NIL and ZAL for earthquakes and underground nuclear explosions were obtained from the prototype-International Data Center (pIDC) that has been established for developing monitoring capabilities of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The pIDC discriminant measurements have large scatter, much of which is attributed to wave propagation effects in the heterogeneous crustal waveguide. Linear regressions indicate that the phase ratios are correlated with topographic characteristics along the individual paths, providing an empirical means for correcting for path effects beyond conventional distance corrections. Kriging, a spatial multiple regression algorithm, also reveals coherent spatial patterns in the data indicative of regional path effects. Using available high-resolution topography data, correction of regional P/S ratios for the best models obtained from multivariate regressions systematically reduces the data variance relative to distance corrections alone, as has been observed for other data sets. The reduced scatter in the measurements increases the separation between earthquake and explosion populations in most cases, enhancing the regional discriminant performance. The path-corrected discriminants isolate explosions better for NIL than for ZAL, even though some of the explosion sources are located in a common source area. Kriging achieves comparable or superior variance reduction for the discriminant measures, without requiring knowledge of the path structure, although this may not result in improved discriminant performance. While always desirable, corrections for heterogeneous path effects may prove inadequate in some cases, notably when phase blockage occurs or when strong attenuation eliminates the diagnostic high-frequency energy.     

Site Effects and Design Provisions: The Case of Euroseistest

—?Modern seismic codes usually include provisions for site effects by considering different coefficients chosen on the basis of soil properties at the surface and an estimate of the depth of bedrock. However, complex local geology may generate site amplification on soft soils significantly larger than what would be expected if we assume that the subsoil consists of plane soil layers overlaying a homogeneous half-space. This paper takes advantage of the large number of previous studies of site effects done at Euroseistest (northern Greece). Those studies have supplied a very detailed knowledge of the geometry and properties of the materials filling this shallow valley. In this paper we discuss the differences between site effects evaluated at the surface using simple 1-D computations and those evaluated using a very detailed 2-D model of the subsoil structure. The 2-D model produces an additional amplification in response spectra that cannot be accounted for without reference to the lateral heterogeneity of the valley structure. Our numerical results are extensively compared with observations, which show that the additional amplification computed from the 2-D model is real and affects by a significant factor response spectra, and thus suggests that some kind of aggravation factor due to the complexity of local geology is worthy of consideration in microzonation studies and seismic codes.