沂沭断理解带（山东段）断层系统分维几何学特征

地表的断裂分布具有复杂的几何结构，分形几何学是定量研究断裂复杂性和破碎性的一种数学方法，本文应用分维几何学的方法，在比例尺为1：50万的山东省构造体系图上，对沂沭断裂带（山东段）（以下简称沂沭带）断层系统进行了分段解析、计算，并得到了各段的分维值。沂沭带全带断层的分维值为1.34，南段分维值为1.29，北段分维值为1.41，结果表明，分维可以表征断层的不均匀性、不规则性和复杂性等。与沂沭带地震活动南高北低情况对比认为，断层系统分维低的地区地震活动性可能较高。     

洛杉矶盆地中的地震波形模拟

最近发生的几次地震与洛杉矶盆地邻近,这为提取盆地对地震波传播的影响提供了机会。1987年10月4日发生的惠蒂尔峡谷地震序列中的一次余震(M_L=5.3)和1991年4月28日发生的谢拉马德雷主震(M_L=5.8)在盆地最深处各台站所构成的方位角相近。盆地各台站所得到10月4日余震记录有一显著特点,即S,SS等多重反射波振幅很大。切向分量上其振幅高达直达S波振幅的2倍。在小于25km的这样一个小范围内,需要一个水平方向的地震波速度梯度,使地震射线足够快地发生弯曲,以形成这些多重反射波。本文采用了一种正演模拟方法,用有限差分数字技术得到双力偶点源震源机制。以洛杉矶盆地东端一个近代地质横断面为依据的模型生成的震相比在地震记录中所看到的震相要多。而以顶部几层中低剪切速度的倾斜分层为依据的较简单的模型,与资料拟合得更好。为了符合直达P波、直达S波和第一个多重S波之间的到时差,要改变地震速度、深度、层的倾斜等输入参数。尽管第一个多重波的相位与资料不符,但直达S波和第一个多重S波初动脉冲的到时、振幅模拟得很好。除了在邻近盆地边缘的距离内,盆地模型中加进陡峭的西部边界,对合成波形没有多大影响。在盆地最深部分SS波的振幅是最大的,比直达S波大2倍。从东北到西南,尾波持续时间从8s增加到20多秒。谢拉马德雷主震发生在惠蒂尔峡谷地震序列的东北部25km左右。惠蒂尔峡谷的模型被扩展到这一距离范围,在惠蒂尔地震和谢拉马德里地震震中之间设置一浅盆地,以模拟圣加布里埃尔沉积盆地。虽然由深盆地边缘产生的震相仍然控制着合成波形,但该模型产生了一个长的尾波。这一研究表明:穿过深沉积盆地,频率达1Hz的若干特定震相可以用二维地震波速度模型来解释。     

Grid resolution study of ground water flow and transport

Three-dimensional grids representing a heterogeneous, ground water system are generated at 10 different resolutions in support of a site-scale flow and transport modeling effort. These grids represent hydrostratigraphy near Yucca Mountain, Nevada, consisting of 18 stratigraphic units with contrasting fluid flow and transport properties. The grid generation method allows the stratigraphy to be modeled by numerical grids of different resolution so that comparison studies can be performed to test for grid quality and determine the resolution required to resolve geologic structure and physical processes such as fluid flow and solute transport. The process of generating numerical grids with appropriate property distributions from geologic conceptual models is automated, thus making the entire process easy to implement with fewer user-induced errors. The series of grids of various resolutions are used to assess the level at which increasing resolution no longer influences the flow and solute transport results. Grid resolution is found to be a critical issue for ground water flow and solute transport. The resolution required in a particular instance is a function of the feature size of the model, the intrinsic properties of materials, the specific physics of the problem, and boundary conditions. The asymptotic nature of results related to flow and transport indicate that for a hydrologic model of the heterogeneous hydrostratigraphy under Yucca Mountain, a horizontal grid spacing of 600 m and vertical grid spacing of 40 m resolve the hydrostratigraphic model with sufficient precision to accurately model the hypothetical flow and solute transport to within 5% of the value that would be obtained with much higher resolution.     

Evidence of chromosomal damage in common eiders (Somateria mollissima) from the Baltic Sea

Common eiders nesting in the Baltic Sea are exposed to generally high levels of contaminants including potentially genotoxic polycyclic aromatic hydrocarbons and organochlorines. Blood samples were collected from eiders at eight sites in the Baltic Sea and two sites in the Beaufort Sea. DNA content variation was estimated using the flow cytometric method, and subsequently utilized as a biomarker of genetic damage. We observed no significant differences in genetic damage among populations within either the Baltic or Beaufort Seas. However, eider populations from the Baltic Sea had significantly elevated estimates of genetic damage compared to populations from the Beaufort Sea.     

Do conservative solutes migrate at average pore-water velocity?

According to common understanding, the advective velocity of a conservative solute equals the average linear pore-water velocity. Yet direct monitoring indicates that the two velocities may be different in heterogeneous media. For example, at the Camp Dodge, Iowa, site the advective velocity of discrete Cl- plumes was less than one tenth of the average pore-water velocity calculated from Darcy's law using the measured hydraulic gradient, effective porosity, and hydraulic conductivity (K) from large-scale three-dimensional (3D) techniques, e.g., pumping tests. Possibly, this difference reflects the influence of different pore systems, if the K relevant to transient solute flux is influenced more by lower-K heterogeneity than a steady or quasi-steady water flux. To test this idea, tracer tests were conducted under controlled laboratory conditions. Under one-dimensional flow conditions, the advective velocity of discrete conservative solutes equaled the average pore-water velocity determined from volumetric flow rates and Darcy's law. In a larger 3D flow system, however, the same solutes migrated at approximately 65% of the average pore-water velocity. These results, coupled with direct observation of dye tracers and their velocities as they migrated through both homogeneous and heterogeneous sections of the same model, demonstrate that heterogeneity can slow the advective velocity of discrete solute plumes relative to the average pore-water velocity within heterogeneous 3D flow sytems.     

Analysis of bacterial diversity and metals in produced water, seawater and sediments from an offshore oil and gas production platform

Produced water is one of the largest waste products routinely discharged into the ocean from offshore oil and gas platforms. This study analyzed bacterial communities and metals in the produced water, surrounding seawater, and sediment around the Thebaud platform. The bacterial community within the produced water was different from the seawater (SAB = 13.3), but the discharge had no detectable effect on the bacterial communities in the seawater (SAB > 97). In contrast, genomic analysis of sediments revealed that the bacterial community from 250 m was different (SAB = 70) from other locations further from the discharge, suggesting that the produced water had a detectable effect on the bacterial community in the sediment closest to the discharge. These near-field sediments contained elevated concentrations of manganese and iron that are associated with the produced water effluent. The results suggested that the discharge of produced water has influenced the bacterial community structure of sediments adjacent to the platform.