Modelling S-wave radiation for SP-waves in isotropic and anisotropic media

Utilizing shear-wave (S-wave) data acquired with compressional waves (P-waves) is becoming more common as joint imaging and inversion techniques improve. Interest in S-waves radiated from vertical sources and buried explosives exploits conversion to P-waves as primary reflections (SP-waves) for reducing acquisition costs and for application to legacy data. However, recent investigations overstate the extent of SP-wave illumination and show isotropic processing results with narrow bandwidth frequency and wavenumber data. I demonstrate that illumination with SP-waves is limited in general to near vertical polar angles up to around 30° or 35° for V_P/V_S of 2 or 3, respectively. At greater angles, S-waves are typically in the P-wave evanescent range and cannot excite SP-wave reflections. Contrary to recent claims, these sources for P-wave do not radiate S_H-waves polarized in horizontal planes in all azimuths. I show these properties for isotropic media with radiation expressions for amplitude derived in vector slowness coordinates. Also, I extend these expressions to transversely isotropic media with a vertical symmetry axis to show agreement with synthetic seismic data that only quasi S_V-waves are radiated and become more narrowly focused towards 45°. Furthermore, in orthorhombic media, synthetic data show that fast S₁- and slow S₂-waves polarized parallel and perpendicular to fractures may appear as S_V- and S_H-waves. For the partially saturated fracture model studied here, S₁-wave radiation has broader azimuthal illumination than slow S₂-waves, which are more narrowly focused in azimuth. These produce SP-wave splitting signatures on vertical component reflection data that are nearly identical to PS-wave signatures on radial horizontal component data. Separating these fast and slow SP-waves is an additional processing challenge.     

基于稀疏约束和多源激发的地震数据高效采集方法

地震勘探目标日趋复杂化和精细化,"两宽一高"等采集技术获得了广泛应用,从而导致当前地震数据采集周期越来越长、成本越来越高,如何解决日益增长的勘探成本问题成为当前地震采集领域的研究热点之一.针对上述问题,本文首先开展了基于稀疏性的地震数据高效采集方法理论研究,对地震数据稀疏性基本理论、稀疏约束下随机采样及其数据重建方法进行了深入探讨,提出使用改进的分段随机采样方法灵活地进行实际地震采集测网设计;详细阐述了多源地震激发方法,对多源地震数据分离方法开展了深入研究,提出了基于小窗口中值滤波与稀疏约束联合随机去噪的多源数据分离方法,并在数据分离处理中取得了较好的效果;将上述两种地震数据采集方案有机结合,提出了1)规则多源、随机检波点(DmsRg)、2)随机多源、规则检波点(RmsDg)和3)随机多源、随机检波点(RmsRg)等三种高效采集方案及相应的数据重建方案,满足了后续常规化数据处理的要求,并讨论了多源激发对数据成像的影响.基于Marmousi模型数据的数值试验表明,本文构建的基于稀疏约束和多源激发的高效采集方法理论对于提高地震数据采集效率、降低勘探成本具有重要的应用价值,建立的数据重建方法流程可以取得和常规数据接近的成像结果.本文方法虽然在数值试验中取得了较为理想的效果,但还需要得到野外实际数据采集的进一步检验.     

Sediment dynamics in the Castleton karst,Derbyshire, U.K.

Chemical and mineralogical data are presented for a suite of 59 sediment samples collected from the P8 and Speedwell cave systems (and mineralogical data are presented for a further six surface sediments) in the Castleton karst catchment, Derbyshire, England. Sediments are grouped according to age and depositional environment and these groups show distinctive mineralogical and chemical characteristics. Clay mineralogy is effective at distinguishing different sediment sources for ancient and modern sediments which are derived from pre-Devensian tills and Devensian solifluction deposits, respectively. Major element chemistry reflects these differences in clay mineral content, while trace elements demonstrate the importance of abrasion of ore minerals in conduits in the aquifer which follow mineral veins, even under natural, pre-mining conditions. Clay minerals are confirmed as the host for uranium in uranium-rich ancient sediments. Consideration of organic carbon and hydrogen concentrations shows that plant material is the dominant source of organic material in the modern sediments. Copyright © 1999 John Wiley & Sons, Ltd.     

系统聚类逐步判别法对皖北矿区突水水源的分析

以Ca2+、Mg2+、K++Na+、Cl-、SO₄2-、CO₃2-、HCO₃-、pH值与TDS的测试结果为指标,对皖北矿区四含、煤系、太灰、奥灰4个主要突水含水层系统分别进行聚类分析。在此基础上,筛选出能代表各含水层水化学特征的水样进行逐步判别分析,并从中选出了SO₄2-与TDS两种标型组分,建立了皖北矿区突水水源的判别模型,该模型具有较好的判别效果。      

新疆沙尘源状况及其沙尘气溶胶释放条件分析

沙尘气溶胶是干旱、半干旱区大气中重要的组成物质, 沙尘天气多发是该区域沙尘气溶胶含量高的主要原因。新疆1/4的土地被沙漠覆盖,塔里木盆地绝大部分地区沙土和沙壤土占地比率大于60%,沙漠沙以细沙为主, 特殊的下垫面为沙尘天气的形成提供了丰富的沙源;沙漠周围的边缘地带、河流两岸、古河道中的土壤类型中粒径小于2.5 μm和粒径小于10 μm的土壤颗粒物中细颗粒物分别达到了50%和20%,是大气沙尘气溶胶中细颗粒物的主要来源和潜在来源。沙尘天气的产生受大风、降水、植被覆盖度、下垫面性质以及大气环流等多种因素的影响。     

储油罐气态污染物计算方法的选择及污染控制

储罐无组织排放的定量估算是石化企业污染源核查的重要项目。通过对比分析美国国家环保局(EPA)、美国石油学会(API)及中国石油化工(CPCC)系统经验公式等3种常用定量方法的应用情况,选择储罐区预测大气污染物的最佳方法,进而确定对储油罐的油品蒸发损耗量。结果表明:采用浮顶罐可减少小呼吸损耗,设置油气回收设施可减少大呼吸损耗,EPA公式较适合轻质油品,CPCC公式较适合拱顶罐,并提出减少油品损耗量的防治措施。     

中印度洋洋盆GC11岩心富稀土深海沉积的元素地球化学特征

对中印度洋洋盆的沉积GC11岩心开展了主量元素、微量元素和稀土元素分析研究,根据主微量元素相关性特征、稀土元素富集程度以及澳大利亚后太古代平均页岩归一化模式特征,初步探讨了GC11岩心的沉积地球化学特征,以及影响稀土元素富集的可能因素。研究表明,GC11岩心稀土元素总量在400.64×10?6～742.74×10?6,平均值为658.41×10?6,略低于邻近海域的GC02岩心,与沃顿海盆DSDP213岩心中含沸石型深海粘土层位中的稀土元素含量相当。δCe负异常明显,(La/Yb)_N为0.42,显示重稀土相对富集的特点。稀土元素与P₂O₅呈显著正相关性,CaO/P₂O₅的平均值为2.3,表明生物钙磷灰石可能是稀土元素的主要载体矿物,而铁锰水合物可能对富集稀土元素有一定的促进作用,但影响不大;GC11岩心中δCe负异常程度远低于GC02岩心,略低于DSDP213岩心,中稀土富集特征与GC02和DSDP213岩心基本一致。不同程度陆源物质的混入可能是导致以上不同岩心中稀土元素富集程度和分馏特征的主要原因。     

基于水环境化学及稳定同位素联合示踪的土地利用类型对地下水体氮素归趋影响

识别复杂土地利用类型对地下水体氮素归趋的影响一直是非点源污染研究中的重点及难点。本文采用水环境化学及同位素联合示踪法对具有复杂地类的三江平原阿布胶河流域地下水体中氮素归趋进行解析研究。结果表明：研究区域内地下水体中存在严重的氮素污染,部分点位超出标准限值近4倍。土地利用类型不仅是氮素浓度和水化学类型演变的主导因素,而且对地下水体氮素循环过程及氮素来源产生了重要的影响。其中：在林地区域内,硝态氮占主导,氮素主要来源于土壤有机氮硝化;在城镇区域内,硝态氮超标,具有较高的氯离子浓度,主要来源于粪便及废水,受硝化过程所控制;在水田区域：铵态氮超标,具有较高的硝酸盐同位素值（δ ¹⁵N-NO₃ ^-和δ ¹⁸O-NO₃ ^-）且二者存在显著的线性关系,表明存在着显著的反硝化过程。在旱田区域,硝态氮占主导,氮素来源及循环过程较为复杂,受反硝化及雨水混合过程等多重影响,难以单一使用同位素示踪法进行溯源解析。通过联合水化学解析法能进一步揭示该区域氮素污染主要来源于肥料施用。因此,通过联合示踪法能够补充复杂土地利用区域氮素来源识别工作的缺陷,提升地下水体氮素归趋识别的精度。     

山东省广饶县土壤重金属来源、分布及生态风险

选取山东省广饶县作为研究区,采集300个表层土壤样品（0~20 cm）,测定As、Cd、Co、Cr、Cu、Hg、Mn、Ni、Pb和Zn等10种重金属含量;运用多元统计和地统计分析方法揭示广饶县土壤重金属元素的来源与空间分布特征,最后利用H?kanson潜在生态风险指数法评价重金属的潜在生态风险。结果表明：① 研究区土壤中Co和Pb的平均值低于山东省背景值,其他8种元素的平均值均超过山东省背景值;特别是Cd和Hg的平均含量分别达到山东省背景值的1.86倍和2.50倍,说明在土壤中存在明显的富集。② As、Co、Cr、Cu、Mn、Ni和Zn为自然源,受成土母质控制;Hg为人为源,主要来源于煤炭燃烧和工业排放;Cd和Pb受自然和人为因素共同控制。③ 成土母质控制着As、Cd、 Co、Cr、Cu、Mn、Ni、Pb和Zn的基本分布格局,不同土地利用类型的土壤Hg含量差别较明显,其高值区集中在城镇建设用地。④ 总体上,研究区为中等生态风险的偏高水平,其中Cd和Hg分别为中等和较高生态风险,其余8种元素处于低生态风险。     

Floc meal as potential substitute for soybean meal in tilapia diets under biofloc system conditions

This study was conducted to evaluate the ef fect of replacing soybean meal(SBM) by low protein ?oc meal(LPFM; 24% CP) in tilapia diets on growth performance, feed utilization and ?sh chemical composition. Three isonitrogenous and isocaloric diets were formulated; control diet(C; without LPFM),FM 25(25% of SBM protein was substituted by LPFM) and FM 50(50% of SBM protein was substituted by LPFM). Nine 55 l circular plastic tanks were stocked by 12 ?sh to form three experimental groups.No dif ferences in tilapia performance were observed between the control and the FM 25 diet. Chemical composition of ?sh did not dif fer signi?cantly among treatments except for protein and selenium contents where the highest values were recorded in the control treatment. The highest mineral content was recorded in ?oc collected from the control tanks, while calcium content showed its highest value in ?oc collected from FM 50 e ? uent. These data indicate that replacing soybean meal with LPFM up to 25%, had no negative ef fect on growth performance and potentially may improve the system sustainability. Meanwhile, the adverse ef fect of more inclusion of LPFM in tilapia diet may be attributed to the higher content of ash. In other word,minerals seem to cause more energy utilization in ?sh fed ?oc meal since it is needed to maintain osmotic homeostasis.