页岩中水力压裂扩展的微震机理研究

微震监测技术被广泛应用于衡量水力压裂作用.由于微震释放机制的复杂性,很难获得对其统一的理论认识.基于地震学原理,本文采用物理模拟实验和数值分析方法对页岩水力压裂扩展造成微震的机制进行研究.理论上,岩石破裂过程取决于水力裂纹尖端的应力分布.通过反演得到矩张量的特征方程及其特征值,从而确定震源点的破裂机制.通过真三轴水力压...     

硫酸侵蚀碳酸盐岩对长江河水DIC循环的影响

对长江及其主要支流河水水化学和溶解无机碳（DIC）同位素组成（δ13GDIC）进行了研究。河水阳离子组成以Ca^2＋、Mg^2＋为主,阴离子以HCO3-、SO4^2-为主,水化学组成主要受流域碳酸盐岩矿物的化学侵蚀控制。DIC含量为0．3～2．5mmol／L,从上游到河口逐渐降低。δ13CDIC值为-12．0‰-3．4‰,与DIC含量具有相似的变化趋势。H2CO3溶解碳酸盐岩是控制河水DIC来源及其占δGDIC组成的主要机制。H2SO4溶解碳酸盐岩加剧了流域碳酸盐岩的化学侵蚀,一方面导致了河水的DIC含量增加,另一方面也使河水的δ13GDIC值升高。     

地下水中氡底数和异常浓度的形成及其普查的意义

含氢地下水,即氢浓度增高的水(超过36爱曼),系矿水的一种,它可用于矿泉医疗。假如对地下水中氢的底数浓度和异常浓度的形成条件有正确的概念,那么这种水也能作为寻找放射性矿床的普查标志。促成地下水氢的富集的基本因素之一是被地下水冲洗的岩石中镭的绝对含量。但是,目前对岩石中放射性元素分布规律的知识尚很有限。尼柯诺夫认为,近十年来总趋势是:过去采用过的岩石中放射性元素含量值是下降,而且接近岩浆岩和沉积岩的平均值。从尼柯諾夫文章中借用的、并经维诺格拉多夫的资料加以补充的表l     

A New Species of Tsuga (Pinaceae) based on Lignified Wood from the Late Miocene of Central Yunnan, China, and Its Paleoenvironmental Implications

A new species, Tsuga nanfengensis sp. nov. (Pinaceae), is described on the basis of lignified fossil wood from the late Miocene of the Xianfeng Basin, central Yunnan, southwestern China. Detailed observation of the fossil wood specimens show the following characteristics: distinct growth rings, absence of resin canals, uniseriate bordered pits in the radial wall of tracheids, ray tracheids and piceoid and cupressoid cross-field pits. These features indicate similarities to the wood of extant Tsuga canadensis, T. chinensis, and T. dumosa. According to the fossil record, Tsuga was present in Xundian County during the Miocene. Today Tsuga is drought intolerant, preferring wet conditions with no extant species growing naturally in Xundian County. The presence of Tsuga in the Miocene of Xundian County indicates a humid climate consistent with previous palaeoclimatic reconstructions showing a wetter and probably shorter dry season in the Miocene, relative to the present day. Therefore, the change in the local climate such as increasing aridity through the Miocene might explain the local extinction of Tsuga from central Yunnan.     

SEDIMENT YIELD AND HYDROLOGY IN NORTHWESTERN RANGELANDS

lINTRODUCTIONRangeandforestlandsofnorthwesternNorthAmericahavebeenutilizedforres0urceextracti0nandproductionsinceinitialhuman0ccupationofthecontinent.Intensive"managed"utilizati0nofec0systemsforspecificbenefitsincludingcattle,sheep,t1sh,w00dandagriculturalpr0ductshasbeenong0ingfornearly0ne-and-haIfcenturies.Intensiveresourceproducti0nhasto0oftenbeenacc0mpaniedbyunwanted"sideeffects"includingacceleratederosion,s0illossandsedimentdeliveredoffsitetod0wnstreamlocati0ns,estuariesandoceanicsin…     

基于序列的地震危险性概率分析

地震通常在时空上是丛集的。传统的地震危险性分析所考虑的只是每个地震丛集中最大震级的事件——主震,并用所考虑场地地震动强度量值的超越率来表示（Cornell,1968）。这种地震危险性概率分析（PSHA）用于长期的结构设计或评估。近来,出于对短期风险的管理,已采用一种类似的方法来进行余震地震危险性概率分析（APSHA）,其与主震的发生相关（Yeoand Cornell,2009）。地震危险性概率分析通常用一种均匀泊松过程来描述事件的发生,而余震地震危险性概率分析则通过有条件的非均匀泊松过程来模拟余震的发生,其概率值取决于触发余震序列的主震震级。另外,由主震和后续余震组成的每个地震丛集,可以看成以相同主震概率发生的单一事件。这就可以用相对简单的方式在危险性分析中考虑余震,这个方法首先由Toro和Silva（2001）论证,并由Boyd（2012）进一步研究。实际上,这篇短文中心探讨概率方面,说明地震危险性概率分析和余震地震危险性概率分析的联合结果以得到一种考虑主震一余震序列的地震危险性整体解析解的可行性,而前面提到的研究中这些仍然缺乏。这种方法应用的结果,说明有助于依据导致超越某一加速度阈值同时也考虑余震的地震事件发生率（如对于结构设计）,初步评估地震危险性的增加。因而这从地震工程长远来看是切合实际的方向。     

Transition from wavelets to ripples in a laboratory flume with a diverging channel

An experimental investigation on the initiation and development of bed forms on a bed of fine silica sand was conducted under alluvial flow conditions in a laboratory flume with a diverging channel. The main aims of the study were to assess： i） the steepness of bed forms in the transition stage of development; and ii） the threshold height of wavelets （ηt） that triggered the start of ripple development. Detailed bed profile measurements were carried out using an acoustic Doppler probe, traversed longitudinally over the sediment bed at various experimentation times. The bed form dimensions were extracted from such bed profile records and analysed for the wavelet, transition and equilibrium stages. It was found that the steepness of ripples in the transition and equilibrium stages were similar, confirming predictions of previous mathematical model simulations. A lognormal distribution fitted the wavelet length data. The wavelet threshold height was estimated as ηt ≈ 7 mm, or ηt≈ 80 in wall units. Such a height magnitude suggested that ripple development could be triggered by the wavelets reaching the outer flow zone of a turbulent boundary layer. The ηt value obtained corresponded generally to the intersection point between two predictive equations for bed form dimensions. A formulation was developed to predict ηt as a function of the sediment grain size, which was confirmed for the fine sand used in this study.     

Evaluation of the Mytilus galloprovincialis Lam. digestive gland metallothionein as a biomarker in a long-term field study: seasonal and spatial variability

A study was made of seasonal and spatial variability of metallothionein (MT) concentrations, determined spectrophotometrically in the soluble fraction of the digestive gland of mussels Mytilus galloprovincialis, collected between 1999 and 2001 from several coastal and estuarine locations along the central Eastern Adriatic coast (Croatia). The seasonal influence on the MT and metal concentrations (higher values in winter-spring season, than in summer-autumn season) is more pronounced than the local site-specific influence. Furthermore, within each season a significant site-specific dependence on the MT and trace metal variations can be detected. An inverse relationship of mussel condition index (CI) and temperature with MT and trace metals levels indicates the influence of food abundance and mussel annual reproductive cycle. Substantially higher concentrations of both MT and Cd were recorded in mussels inhabiting estuarine locations, possibly indicating a markedly higher Cd bioavailability at these locations. The positive correlations obtained between MT and Cd in all seasons except autumn support an argument for application of digestive gland MT as a biomarker of Cd exposure, providing evidence for assessing the most appropriate season for mussel sampling.     

Occurrence of perfluorinated compounds in water, sediment and mussels from the Cantabrian Sea (North Spain)

Perfluorinated compounds (PFCs) have emerged as significant global environmental pollutants with persistent, bioaccumulative and toxic properties. The aim of this study was to determine the occurrence of PFCs in water (wastewater, submarine emissaries and port-waters), sediment and transplanted mussels in estuarine areas of high urban and industrial impact from Northern Spain. Five PFCs of industrial use were studied: perfluorooctanesulfonate, perfluorohexanesulfonate, perfluorobutanesulfonate, perfluorooctanoate acid and perfluorononanoate acid. After selective extraction, samples were analyzed by Ultra Performance Liquid Chromatography coupled to tandem mass spectrometry. ΣPFCs ranged from 0.06 to 10.9 ng/L in water, with higher levels in wastewater treatment plants effluents and port waters than in submarine emissaries. Little accumulation was observed in sediments and mussels with ΣPFCs ranging from 0.01-0.13 ng/g dw and 0.01-0.06 ng/g ww, respectively. Most ubiquitous compounds were PFOS and PFOA. Mass fluxes of PFCs to the Cantabrian Sea are estimated and the impact to the coastal ecosystem is discussed.