碳酸盐岩风化过程中高场强元素的地球化学行为研究——来自碳酸盐岩淋溶实验的证据

选择黔中地区的一条白云岩原位风化剖面（平坝剖面）作为研究对象,通过对岩-土界面之下的岩粉层（砂状碳酸盐岩）动态淋溶过程中高场强元素（HFSE）地球化学行为的研究,并结合其在风化壳剖面的分布特征,获得了以下主要认识:（1）碳酸盐岩风化过程中,HFSE间存在明显的分馏,而且元素分馏主要出现在岩-土界面作用过程中,即碳酸盐岩溶蚀形成残积土阶段;元素的地球化学惰性由强到弱的顺序依次为Zr>Hf>Nb>Sc>Th>Ta>Ti>Y,其中,Zr是最稳定的元素,Hf仅次于Zr,Nb和Sc也相对较为惰性,而Th、Ta、Ti、Y呈现出明显的活性;（2）对于碳酸盐岩风化剖面的质量平衡计算,Zr是理想的参比元素（即惰性元素）;（3）由基岩酸不溶物至风化壳剖面,元素对Nb-Ta、Zr-Hf显示出较好的协变性,没有明显分馏,因此,在利用这类元素对岩溶区风化壳的物源进行示踪时,碳酸盐岩作为潜在母岩,宜采用其酸不溶物作为参比对象;（4）碳酸盐岩风化过程中,虽然Sc也是一个较为稳定的HFSE,但在风化母岩中分布不均匀,不宜用于岩溶区风化壳的物源示踪。      

Assessment of groundwater recharge processes through karst vadose zone by cave percolation monitoring

Recharge processes of karst aquifers are difficult to assess given their strong heterogeneity and the poorly known effect of vadose zone on infiltration. However, recharge assessment is crucial for the evaluation of groundwater resources. Moreover, the vulnerability of karst aquifers depends on vadose zone behaviour because it is the place where most contamination takes place. In this work, an in situ experimental approach was performed to identify and quantify flow and storage processes occurring in karst vadose zone. Cave percolation monitoring and dye tracing were used to investigate unsaturated zone hydrological processes. Two flow components (diffuse and quick) were identified and, respectively, account for 66% and 34% of the recharge. Quickflow was found to be the result of bypass phenomenon in vadose zone related to water saturation. We identify the role of epikarst as a shunting area, most of the storage in the vadose zone occurring via the diffuse flow component in low permeability zones. Relationship between rainfall intensity and transit velocity was demonstrated, with 5 times higher velocities for the quick recharge mode than the diffuse mode. Modelling approach with KarstMod software allowed to simulate the hybrid recharge through vadose zone and shows promising chances to properly assess the recharge processes in karst aquifer based on simple physical models.     

Quantitative analysis of riverbank groundwater flow for the Qinhuai River,China, and its influence factors

Interactions of surface water and groundwater (SW–GW) play an important role in the physical, chemical, and ecological processes of riparian zones. The main objective of this study was to describe the two‐dimensional characteristics of riverbank SW–GW interactions and to quantify their influence factors. The SW–GW exchange fluxes for six sections (S1 to S6) of the Qinhuai River, China, were estimated using a heat tracing method, and field hydrogeological and thermodynamic parameters were obtained via inverse modelling. Global sensitivity analysis was performed to compare the effects of layered heterogeneity of hydraulic conductivity and river stage variation on SW–GW exchange. Under the condition of varied river stage, only the lateral exchange fluxes at S1 apparently decreased during the monitoring period, probably resulting from its relatively higher hydraulic conductivity. Meanwhile, the SW–GW exchanges for the other five sections were quite stable over time. The lateral exchange fluxes were higher than the vertical ones. The riverbank groundwater flow showed different spatial variation characteristics for the six sections, but most of the higher exchange fluxes occurred in the lower area of a section. The section with larger hydraulic conductivity has an apparent dynamic response to surface water and groundwater level differences, whereas lower permeabilities severely reduced the response of groundwater flow. The influence of boundary conditions on SW–GW interactions was restricted to a limited extent, and the impact extent will expand with the increase of peak water level and hydraulic conductivity. The SW–GW head difference was the main influence factors in SW–GW interactions, and the influence of both SW–GW head difference and hydraulic conductivity decreased with an increase of the distance from the surface water boundary. For each layer of riverbank sediment, its hydraulic conductivity had greater influence on its groundwater flow than the other layers, whereas it had negligible effects on its overlying/underlying layers. Consequently, the variations in river stage and hydraulic conductivity were the main factors influencing the spatial and temporal characteristics of riverbank groundwater flow, respectively.     

九江下蜀黄土的常量元素组成及其物源指示

长江中下游地区下蜀黄土的物质来源一直是个热点问题。本文对江西九江下蜀黄土和甘肃临洮晚更新世以来黄土的常量元素组成进行了研究,并与末次间冰期以来黄土高原其它点位的黄土、长江中下游其它地点的下蜀黄土和长江沉积物的元素组成进行对比,以期探讨九江下蜀黄土的物质来源。结果表明：（1）九江下蜀黄土的地球化学元素以SiO2、Al2O3、Fe2O3为主。与临洮黄土的元素组成相比,九江下蜀黄土具有较高的SiO2、Al2O3、Fe2O3、TiO2含量和较低的CaO、MgO含量。（2）在空间上,下蜀黄土的SiO2/Al2O3比值未表现出黄土高原黄土（北方黄土）的SiO2/Al2O3比值随纬度规律性变化的特点,揭示下蜀黄土的主要源区可能不是北方的内陆荒漠或黄土高原。（3）TiO2/Al2O3-K2O/Al2O3和TiO2/Al2O3-Fe2O3/Al2O3图解显示下蜀黄土与北方黄土存在显著差异,进一步表明下蜀黄土与北方黄土的主要源区可能不同。     

Chaotic ray behaviour in regional seismology

Rays propagating through strongly laterally varying media exhibit chaotic behaviour. This means that initially close rays diverge exponentially, rather than according to a power law. This chaotic behaviour is especially pronounced if the medium contains laterally varying interfaces. By studying simple 2-D and 3-D versions of models with laterally varying interfaces, the importance of chaotic ray behaviour is determined. A model of the Moho below Germany produces sharp variations with epicentral distance of the number of arrivals. In addition, the number of caustics grows dramatically: up to 1200 caustics are present between a distance of 0 and 800 km. Using the theory of Hamiltonian systems, a more in-depth study of the chaotic character of the ray equations is obtained. It is found that for realistic heterogeneous models most of the relevant rays will exhibit chaotic behaviour. The degree of chaos is quantified in terms of predictability horizons. Beyond the predictability horizons ray tracing cannot be carried out accurately. For the models under consideration, the length from the source to the predictability horizon has an order of magnitude of 1000 km. The chaotic behaviour of the rays makes it necessary to use extensions of asymptotic ray theory, such as Maslov theory, to compute seismic waveforms. It is shown that pseudo-caustics, an important obstacle in computing Maslov synthetics, are a generic feature of the 2-D laterally varying models that are studied. Eventually, the use of asymptotic methods is restricted because of the inaccuracy in the computation of the ray paths.     

地震折射波资料解释中射线方法应用的进一步探讨

开鲁陆家堡凹陷内断裂发育、构造复杂,垂直于构造走向跨度30km,凹陷边缘和凹陷内古生界基底顶板埋深分别为1km和5km,在此开展了基底折射波地震勘探。在已知资料基础上,我们用多段倾斜单界面折射波正演理论计算作指导,设计了野外试验和初步的生产观测系统,t_0和差异时距曲线解释方法对于应用于如此复杂的构造地区其准确性和精度受到了限制。因此,我们在解释方法上试做了如下工作:①多段倾斜单界面折射波理论正演走时拟合,给出较有益的反演解释结果;②二维非均匀介质中射线追踪解释方法,提供准确的射线途径给出基底面上下详尽的更为符合实际的二维速度分布信息。     

用于图像重建的波前法射线追踪

本文给出一种基于Huygens-Fresnel原理的射线追踪方法--波前法.该方法精度高、计算速度快,不仅可给出波从源点传播到接收点的透射走时和射线路径,而且可给出任何时刻的波阵面,为层析成像提供了一种有效的射线追踪方法.     

快速射线追踪及其在地震层析中的应用

在地震层析研究中,常常涉及地震波在非均匀介质中的传播路径问题,故快速射线追踪是不可缺少的工具。本文讨论了一种以三点法为基础的逐步逼近的射线追踪方法,其优点是计算速度快、精度高,适合地震层析研究的计算要求。     

Theory of anisotropic dynamic ray tracing in ray-centred coordinates

A 4×4-propagator matrix formalism is presented for anisotropic dynamic ray tracing, including the propagation across curved interfaces. The computations are organised in the same way as in ervený's well-known isotropic propagator matrix formalism. Attention is paid to cases where double eigenvalues of the Christoffel matrix result in unstable expressions in the dynamic ray tracing system, but where geometrical spreading is well-behaved.