矿产预测中成矿信息的提取和强化     

浦志伟  朱裕生 《地质论评》1993,39(6):508-514

成矿信息的提取是矿产预测的重要手段,其方法的有效性直接影响到预测成果的可靠性。在成矿规律研究的基础上,有意识地干预模型的构成,突出与成矿有关的信息;抑制某些成矿意义不明显和属干扰的信息,有目的地使模型向反映成矿信息的方向逼近,提高模型与矿床实际赋存地质环境的吻合程度,均是成矿信息提取和强化的内涵。本文从研究实践中总结了先验约束模型和非先验约束模型的强化方法,在新疆阿勒泰地区的地质－找矿工作中已取得  相似文献   

On some problems of seismic crustal phase     

葛焕称 《地震学报(英文版)》1995,8(1):57-63

ＯｎｓｏｍｅｐｒｏｂｌｅｍｓｏｆｓｅｉｓｍｉｃｃｒｕｓｔａｌｐｈａｓｅＨｕａｎ－ＣｈｅｎｇＧＥ（葛焕称）（ＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕｏｆＪｉａｎｇｓｕＰｒｏｖｉｎｃｅ,Ｎａｎｊｉｎｇ２１００１４,Ｃｈｉｎａ）Ａｂｓｔｒａｃｔ：Ｉｎｔｈｉｓ...  相似文献   

井下记录的PP和SS震相     

乌统昱  赵惠君 《地震地磁观测与研究》1992,13(2):20-26

本文在系统分析静海台井下地震记录图的基础上,发现并解决了具有一定实际和理论意义的两个问题:其一是证明了最初误认为是干扰的“双脉冲”图形实际上均是微地震。从而指出研究静海周围地区的地震活动性应考虑微震活动问题。其二确认静海周围地区微震波形的4个主要震相是P、PP、S和SS,并对地面反射波PP和SS能够观测到的条件作了初步分析,其结果进一步说明井下地震记录较之地面记录更为“逼真”,复杂和丰富。  相似文献   

Scattering of elastic waves by a fracture zone containing randomly distributed cracks     

Jun Kawahara  Teruo Yamashita 《Pure and Applied Geophysics》1992,139(1):121-144

We theoretically study the scattering ofP, SV andSH waves by a zonal distribution of cracks, which simulates a fault fracture zone. An investigation is conducted how the geometrical properties of the crack distribution and the frictional characteristics of the crack surface are reflected in the attenuation and dispersion of incident waves, as well as in the amplitudes of the transmitted and reflected waves from the zone. If the crack distribution within the fault zone changes temporally during the preparation process of the expected earthquake, it will be important for earthquake prediction to monitor it, utilizing the scattering-induced wave phenomena.We consider the two-dimensional problem. Aligned cracks with the same length are assumed to be randomly distributed in a zone with a finite width, on which elastic waves are assumed to be incident. The distribution of cracks is assumed to be homogeneous and sparse. The crack surface is assumed to be stress-free, or to undergo viscous friction; the latter case simulates fluid-filled cracks. The opening displacement of the crack is assumed to be negligibly small. The idea of the mean wave formalism is employed in the analysis, and Foldy's approximation is assumed.When the crack surface is stress-free, it is commonly observed for every wave mode (P, SV andSH) that the attenuation coefficientQ ^–1 peaks aroundka1, the phase velocity is almost independent ofk in the rangeka<1 and it increases monotonically withk in the rangeka>1, wherek is the intrinsicS wavenumber anda is the half length of the crack. The effect of the friction is to shift the peak ofQ ^–1 and the corner of the phase velocity curve to the low wavenumber range. The high wavenumber asymptote ofQ ^–1 is proportional tok ^–1 independently of model parameters and the wave modes. If the seismological observation thatQ ^–1 ofS waves has a peak at around 0.5 Hz in the earth's crust is combined with our results, the upper limit of crack size within the crust is estimated about 4 km. The information regarding the transmitted and reflected waves, such as the high wavenumber limit of the amplitude of the transmitted wave etc., allows estimation of the strength of the friction.  相似文献   

DDT residue in soil and water in and around the abounded area of DDT manufacturing factory     

Mohammad Rasul Jan Mahmood A Khawaja Jasmin Sha Kashif Gul 《中国地球化学学报》2006,25(B08):182-182

Due to the persistent nature of DDT, a persistent organic pollutant and its adverse environmental and health impacts, the present study was undertaken to examine the residual DDT in and around DDT manufacturing factory in Amman Gharh, Nowshera, NWFP. The factory was established in 1963 and remained in operation till 1994. Composite samples of soil, sediments and water were collected in and around the factory area, nearby DDT stores, main factory drain leading to river and nearby villages. Standard procedures were used for the collection, transportation and storage of samples for analysis. Physical parameters for the collected water samples measured were temperature, pH and conductance. Extraction of each sample for DDT analyses was carried out in triplicates using soxhlet extraction apparatus. The extract was transferred to well washed, clean; dry glass vial, sealed and put in the refrigerator. Gas Chromatograph with electron capture detector and capillary column was used for analysis. DDT in the samples was identified on the basis of their retention time and quantified on the basis of peak areas. It is evident from the analytical data obtained in the present study that both water and soil in and around the factory area are still contaminated with DDT, despite the closure of the factory since the past few years.  相似文献   

Microwave-assisted extraction of organochlorine pesticides from sediments and determination by gas chromatograph with electron capture detection     

Rama Mohan Kurakalva Narasimha Murthy Nyasavajhala Phani Homeshwari Mamidi Venkata Anjaiah Kanukuntla 《中国地球化学学报》2006,25(B08):202-203

A simple and rapid procedure to extract organochlorine pesticides （OCPs） from sediments by means of microwave energy is proposed. Sediment samples were irradiated with microwaves in a closed vessel system while immersed in hexane-acetone （1 ： 1, v/v）. The sample extracts were cleaned up using solid phase extraction with Florisil as adsorbent. Pesticides were eluted with hexane-ethyl acetate （80 ： 20, v/v） and determined by gas chromatographic separation with electron capture detection. Three oven programs were assayed with two different solvent mixtures in order to achieve adequate experimental conditions for the complete extraction of organochlorine pesticides from the matrix. Different variables such as the composition of extraction solvent,  相似文献   

Speciation analysis and significance of ecological geochemistry     

Yaping WANG Chunxue XU Ziyi AN Suming WANG 《中国地球化学学报》2006,25(B08):205-205

Different species of one element have different activities, so it has different effects on environment and human health. To analyze qualitatively and quantitatively the speciation of a special element in sample, which is the important basis for appraising the toxicity and studying the rule of transfer and translation of elements. Since the 1970＇s, the scheme of sequential extraction has already been used at many laboratories both at home and abroard, to get the information about heavy metals＇ activity in polluted soils. Because this method has the experimental nature, many schemes of problem has taken place, the absence of consistency of these sequential extraction have been formed. Thus the complexity of the schemes, the lack of selectivity of reagent, the lack of quality control, the result mainly related to the extraction scheme used, and so on. In the face of these problems, the study of experimental methods of sequential extraction on three different soils, sediment in Dongting Lake, soil in Jiangsu Province and loess in Shanxi Province was made. Reference materials of heavy metal speciation following sequential extraction in soil and sediment had been developed. Nowadays two kinds of sequential extraction methods which are widely used are BCR （three steps） and improved Tessier methods （seven steps）. Based on three steps of BCR, water-soluble speciation and the residual speciation were increased in our research. BCR701 was determined eight times at different laboratories using BCR three steps. The results showed that determined data obtained eight times were identical to the standard value, and it is indicated that this method has good reproducibility. The stability and homogeneity experiments indicated that the preparation of three types of candidates accorded with our requirements. Eight laboratories had afforded the determined values of 12 heavy metal elements （Cu, Pb, Zn, Mn, Co, Ni, Cd, Cr, Mo, As, Sb, Hg, Se et al.） using BCR three steps. Also, these three candidates afforded the determined values by seven steps, and 12 laboratories had participated.  相似文献   

Assessment of mercury mobility and bioavailability by fractionation method in sediments from coastal zone inundated by the 26 December 2004 tsunami in Thailand     

Leonard Boszke  Artur Kowalski  Witold Szczuciński  Grzegorz Rachlewicz  Stanisław Lorenc  Jerzy Siepak 《Environmental Geology》2006,51(4):527-536

The 26 December 2004 tsunami covered significant portion of a coastal zone with a blanket of potentially contaminated sediments. In this report are presented results on mercury concentrations in sediments deposited by the tsunami in a coastal zone of Thailand. Since the total mercury concentrations are insufficient to assess mercury mobility and bioavailability in sediment, its fractionation was applied. Sediments were sampled within 50 days after the event and analyzed by sequential extraction method. The procedure of sequential extraction involved five subsequent stages performed with solutions of chloroform, deionized water, 0.5 M HCl, 0.2 M NaOH, and aqua regia. The mean concentration of total mercury in sediments was 119 ± 50 ng g⁻¹ dry mass (range 66–230). The fractionation revealed that mercury is mainly bound to the least bioavailable sulphides 75 ± 6% (range 62–86), organomercury compounds 14 ± 7% (range 4–26), and humic matter 9 ± 7% (range 1–27). The lowest contributions bring fractions of water-soluble mercury 0.8 ± 1.0% (range 0.1–3.6) and acid soluble mercury 0.9 ± 0.5% (range 0.2–2.1). Although, the total mercury content is similar in a reference sample and in the tsunami sediments, the highly toxic organomercury fraction contribution is higher in the latter. The results were compared with chemical and sedimentological properties of the sediments but no significant correlations were obtained between them.  相似文献   

Distribution of cadmium, chromium, copper, lead and zinc in marine sediments in Hong Kong waters     

S. C. Choi  Onyx W. H. Wai  Thomas W. H. Choi  X. D. Li  C. W. Tsang 《Environmental Geology》2006,51(3):455-461

Partitioning of heavy metals (Cd, Cr, Cu, Pb, Zn) in marine sediments collected from various sites in Hong Kong waters were determined using sequential extraction method. Sediments from Kellette Bank, located in Victoria Harbour, had higher metal concentrations especially Cu and Zn than most other sites. Slightly over 20% of total Cu and Cr existed as readily available forms in Peng Chau and Kellette Bank. At most sampling sites, over 15% of the Cu existed as the exchangeable form indicating that Cu could be readily released into the aqueous phase from sediments. A significantly higher percentage of Pb and Zn was associated with the three non-residual fractions. Hence, there is a greater environmental concern for remobilization of Pb and Zn compared with Cr. The high amount of residual Cd (>50%) and the relatively lower Cd content indicate that little environmental concern is warranted for the remobilization of Cd. Distribution of metals in sediments collected from different depth at Kellette Bank shows that metal concentrations decreased with profile depth. The levels of Pb and Zn associated with the two readily available fractions increased sharply in the surface sediment. These metals represented the pollutants, which were introduced into the area in the mid-eighties through early nineties as a result of rapid economic and industrial development in the territory. As significant portions of these metals were bound to the readily available phases in the surface sediments, metal remobilization could be a concern. An erratum to this article can be found at  相似文献   

Unequal Competition Among Chains of Supercenters: Kmart,Target, and Wal‐Mart     

Thomas O. Graff 《The Professional geographer》2006,58(1):54-64

The three largest discount chains, Kmart, Target, and Wal‐Mart, have adopted the supercenter format for expansion. This article examines the locations of and the competition among these supercenters. Wal‐Mart has the greatest number of supercenters and is driving the expansion of the supercenter format. Both Kmart and Target have clustered their supercenters in a small number of metropolitan markets. In contrast to Wal‐Mart and Kmart, Target has focused on a middle‐class rather than a blue‐collar clientele. Now Kmart is struggling following a declaration of bankruptcy. Wal‐Mart has largely defeated its supercenter competitors and now is confronting the major grocery chains for grocery sales.  相似文献