An approximate F.E. analysis of seepage with a free surface

An approximate step-by-step procedure is presented for the finite element analysis of transient unconfined flow problems. At each step the free surface is modelled by means of segments coinciding with sides of the elements. This leads to an approximate but extremely simple solution scheme which can be readily incorporated into standard codes for confined analysis. The solutions of some significant problems are presented and compared with other non-approximate solutions. They show that the technique, in spite of its approximation, is capable of giving meaningful results from an engineering viewpoint.     

孔道弯曲条件下拉力型锚索锚固段剪应力分布弹性理论分析

随着预应力锚索设计长度的增大,由于地质因素及施工技术的因素造成锚索孔道偏离设计的直线状态,形成具有一定曲率的曲线状态。为探讨拉力型预应力锚索锚固段弯曲条件下剪应力的分布,采用二维弹性理论方法,推导出了解析计算公式,得到锚索锚固段弯曲平面上的最内侧和最外侧的两条曲线上的剪应力分布情况。通过实例计算发现,与锚索孔道直线情况下剪应力分布相比,锚固段弯曲条件下内曲线的剪应力最大值比孔道直线状态时约增大2倍,外曲线的剪应力约为孔道直线状态时的50%,并且在外曲线上出现了约10 cm长度的反方向剪应力。可见,由于孔道弯曲造成了锚固段剪应力分布的不均匀,更易造成锚索内部结构的破坏。     

A record of the behavior of the geomagnetic field in the sediments of Lake Baikal (BDP-99 borehole)

The relative paleointensity of sedimentation is studied for sediments stripped by deep-water drilling in Lake Baikal (BDP-99 borehole). Two intervals are considered: 0–420 ka (Brunhes chron) and 1.05–1.09 Ma (before, during, and after the Matuyama–Jaramillo reversal). For these intervals, curves of the ideal magnetization of samples are plotted.The paleointensity data obtained along the borehole section reveal four excursions for the Baikal sediments whose identification on the inclination–depth curve is complicated.The lower part of the section (Matuyama–Jaramillo subzones) shows a paleointensity decrease by a factor of five or more relative to periods of invariable polarity.     

剪切指向转换的韧性剪切带——中国大陆科学钻探工程(CCSD)主孔中韧性剪切带(深度2010～2145m)的EBSD特征及运动学研究

位于苏鲁超高压变质地体南部的中国大陆科学钻探工程(CCSD)主孔深度1596～2038m的榴辉岩段和2038～2500m的片麻岩段之间存在一条厚一百余米的韧性剪切带(深度2010～2145m).韧性剪切带由糜棱岩化退变榴辉岩、花岗质糜棱岩等强应变岩石组成,韧性剪切带的面理倾向SEE,倾角由上部平均52°向中、下部平均32°转变,拉伸线理产状与面理倾向近一致,是220～200Ma期间折返应变的产物.糜棱岩化退变榴辉岩和花岗质糜棱岩的显微构造与石英晶格优选方位显示了折返阶段早期自SEE向NWW逆冲剪切指向以及后期自NWW向SEE正滑剪切指向转化的应变行为.CCSD主孔2010～2145m韧性剪切带的形成与它位于以榴辉岩为主的岩性.构造单元与其下以片麻岩为主的岩性.构造单元的界线附近有密切联系.第一期超高压阶段南北向韧性剪切作用形成的叶理、拉伸线理产状及相关的岩石类型与第二期、第三期阶段SEE-NWW向折返变形明显不同.     

Native iron in the sediments of Lake Baikal (borehole BDP-98): results of thermomagnetic analysis

We performed a thermomagnetic analysis of 91 samples and a probe microanalysis of five samples of sedimentary rocks from the lower zone of the borehole BDP-98 drilled at the bottom of Lake Baikal. The results show the scarcity of native iron: It was found only in five samples. Its concentration varies from ～10^–5 to 7 × 10^–4%. The distribution of native iron by content is bimodal, with a distinct “zero” mode. This scarcity of native iron in the Baikal sediments distinguishes them from continental (Eurasia) and oceanic (Atlantic) sediments of different ages. It is due to the high rate of sedimentation in the studied interval of BDP-98.     

Extensional shear zones as imaged by reflection seismic lines: the Larderello geothermal field (central Italy)

The Larderello geothermal field is located in the Inner Northern Apennines, in an area which has been subject to extension since the Early Miocene. The latest extensional episode (Pliocene–Present) has resulted in the formation of NW-trending, NE-dipping listric normal faults, whose geometry is controlled down to 3 km by borehole data. In this paper, we integrate a new interpretation of seismic reflection lines with existing seismic, field, and borehole data to analyse the relations among listric normal faults, the top of the brittle–ductile transition, and the migration of geothermal fluids.In accordance with previous interpretations, we consider the strong reflector (K-horizon) marking the top of the reflective mid-lower crust, and located at a depth of 3–5 km in the geothermal area, to represent the top of the brittle–ductile transition. Its reflectivity most probably derives from the presence of overpressured fluids. We identify three main NW-trending, NE-dipping extensional brittle shear zones, showing listric geometry and soling out in the vicinity of the K-horizon. The latter appears to be dislocated in correspondence of the soling out of the shear zones. These shear zones, because of the associated intense fracturing, represent the most natural channels of upward migration of geothermal fluids from the magmatic sources located below the K-horizon.We suggest that these two conclusions—that listric normal faults root at or near the brittle–ductile transition, and that they act as preferential upward migration paths for magmatic fluids—may be of general validity for geothermal fields located in extensional settings.     

Magmatic and hydrothermal R.E.E. fractionation in the Xihuashan granites (SE China)

The Xihuashan stock (South Jiangxi, China) is composed of cogenetic granitic units (granites Xe, a, c, d and b) and emplaced during the Yanshanian orogeny (153±0.2 Ma). They are two feldspars, Fe-rich biotite±garnet and slightly peraluminous granites. Primary accessory minerals are apatite 1, monazite, zircon, uranothorite±xenotime in granites Xe and a, zircon, uranothorite, uraninite, betafite, xenotime 1; hydrothermal minerals are monazite altered into parisite and apatite 2, Y-rich parisite, yttroparisite, Y-rich fluorite and xenotime 2 in granites c and b. Petrographic observations, major element, REE, Y and Rb–Sr isotropic data point to a magmatic suite (granites Xe and a granites c and d granite b) distinct from hydrothermal Na-or K-alteration of b. From granite Xe to granite b, LREE, Eu, Th and Zr content are strongly depleted, while HREE, Y and U content increase. During K-alteration of b, these variations are of minor importance. Major and accessory mineral evidences, geochemical and fluid inclusion results indicate two successive alteration fluids interacting with b, (1) a late-magmatic F^– and CO₂–rich fluid and (2) a post-magmatic, aqueous and slightly saline fluid. The depletion of LREE and Th content and the increase in HREE, Y and U content correspond, in the magmatic suite to the early fractionation of monazite in the granites where there is no hydrothermal alteration (granites Xe and e) and to the hydrothermal alteration of monazite into parisite and secondary apatite, intense new formation of yttroparisite, Y enrichment and U loss in the uranothorite and late crystallization of uraninite in the granites c and b. Moreover, simulated crystallization of monazite and temperature of monazite saturation show early fractionation of monazite from the magma in the less evolved granites (Xe and e) and prevailing hydrothermal leaching of monazite in the most evolved granites (c-d and b) related to a late-magmetic event. The slight variations of REE, Y, Th and U content in the K-altered granites compared to granite b emphazes the distinct chemical nature of the successive hydrothermal fluids. Rb–Sr and Sm–Nd isotopic results point to a 30 Ma period of time between the late-magmatic and the post-magmatic fluid circulation.     

On the nature of temperature variations in borehole kun-1 (Kunashir Island)

The study presents the result of continuous temperature monitoring in a 300 m deep borehole located on the Pacific coast of the Kunashir Island. Temperature variations at of 20–240 m depths with periods from a few tens of minutes to a few tens of days and amplitudes in the order of thousandths to tenths of degree are found to result from three main causes: tidal variations of groundwater level in the borehole, natural convection in the borehole, and nonperiodic and spatially heterogeneous changes of the pore pressure resulting in the appearance of an anomalous subsurface fluid regime and generating crossflow between the different aquifers through the annular space. Joint analysis of temperature and seismic data revealed that shallow-focus (up to 30 km) earthquakes with M > 5 occurred southeast of the seismic station created more expressed temperature response at 240 m depth. This response has the form of a 0.05–0.3 K temperature drop, which precedes a seismic event within a period of a few hours to a few days. Tidal analysis of borehole temperature measurements can be used to calculate the strain sensitivity and the method of borehole temperature monitoring can be used to investigate the tectonic regime of the Earth’s crust.     

Dolomitization and the mineralization of the Marl Slate (N. E. England)

The Marl Slate, the English equivalent of the Kupferschiefer, has been studied with particular reference to the relationships between dolomitization and the origin of the metal sulphides. Dolomite occurs as: 1) discontinuous lenses of ferroan dolomicrite, 2) micronodules of finely crystalline dolospar in association with length-slow chalcedony and 3) discrete laminae of ferroan or non-ferroan dolospar. The ferroan dolomicrite has excess CaCO₃, and is more abundant in the lower, sapropelic facies of the Marl Slate. It is considered to have formed by the penecontemporaneous alteration of calcium carbonate under hypersaline conditions. Small micronodules (typically about 0.3 mm in diameter) are also more abundant in the sapropelic Marl Slate. These frequently contain cores of length-slow chalcedony (quartzine) fibres and sometimes quartz megacrysts. Textural observations clearly indicate that this silica is of authigenic origin and the dolomite/chalcedony micronodules are interpreted as diagenetic replacements of a calcium sulphate mineral such as anhydrite. The discrete laminae of finely crystalline dolospar are often inter-laminated with calcite in the upper part of the Marl Slate. This dolomite is also calcium rich and represents a replacement, possibly of anhydrite, during a later phase of diagenesis. Metal sulphides occur in two distinct forms: as disseminated framboidal pyrite and as discrete lenses of pyrite, chalcopyrite, galena, sphalerite and rarer sulphides. The framboidal pyrite originated during early diagenesis by reaction of sulphide, produced by reduction of sulphate by organic material and micro-organisms, with iron also released in the reducing environment. The sulphide lenses are often in intimate association with dolospar, length-slow chalcedony and authigenic quartz megacrysts. This indicates that the lenses were produced during diagenesis by the reduction and replacement of calcium sulphate (anhydrite). Various sources, such as co-precipitation with dolomite precursors and the underlying Yellow Sands, may have supplied metals which were mobilized and transported by connate brines as diagenesis progressed.     

Rayleigh面波各阶模式频散曲线对横波速度和层厚的敏感性探讨

Rayleigh面波勘探的目的在于有效利用频散曲线反演地层厚度及横波速度,而不同模式的频散曲线对横波速度和层厚的敏感性不同。通过求取介质参数变化10%后与参数不变化时的二组频散曲线的差值,得到各阶模式的频率～相速度差曲线,分析了Rayleigh面波各模式频散曲线对横波速度、层厚的敏感性。试验结果表明,基阶模式对于浅层的横波速度和层厚比较敏感,敏感区域主要集中在较窄的频带范围内。而高阶模式对于相对较深层的横波速度和层厚比较敏感,且频率范围分布较大,敏感性强的频段分布比较分散。研究结果可以为Rayleigh面波多模式联合反演提供理论依据。     

A new velocity field from the analysis of the Egyptian Permanent GPS Network (EPGN)

For studying recent crustal movements and their relation to earthquake occurrence in large scales, the National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Cairo, Egypt started in 2006 the establishment of the Egyptian Permanent GPS Network (EPGN). Beginning with 4 stations in 2007, 15 stations were operational at the end of 2011. In addition, a station in Alexandria of the French “Centre d'Études Alexandrines” (CEALX) was added as station to the EPGN. Nowadays, 16 stations are operational and an extension to 20 in the near future is expected. The collected EPGN data of the last 6 years are used in this work to throw light upon the present state of recent crustal movement of the whole of Egypt. Bernese software V. 5.0 was used for processing the collected data according to the IGS standards. In addition, selected IGS, AFREF, and EPN sites are processed for reference frame definition. In this first comprehensive analysis of the permanent network, a complete and consistent evaluation resulted in the first estimates of present day horizontal velocities and coordinate time series.     

Granitoid rocks of the southern Menderes Massif (southwestern Turkey): field evidence for Tertiary magmatism in an extensional shear zone

Recent field campaign in the southern Menderes Massif in southwestern Turkey revealed that the so-called ‘core of the massif’ comprises two distinct types of granitoid rocks: an orthogneiss (traditionally known as augen gneisses) and leucocratic metagranite, where the latter is intrusive into the former and the structurally overlying ‘cover’ schists. These differ from one another in intensity of deformation, degree of metamorphism and kinematics. The orthogneiss display penetrative top-to-the-N–NNE fabrics formed under upper-amphibolite facies conditions during the Eocene main Menderes metamorphism (MMM), whereas foliation and stretching lineation exists in the leucocratic metagranites but are not strongly developed. The leucocratic metagranites show evidence of syn- to post-emplacement deformation in a series of weakly developed top-to-the-S–SSW fabrics formed under lower greenschist-facies (?) conditions. Leucocratic metagranite bodies occur all along the augen gneiss–schist contact in the southern Menderes Massif; they are emplaced as sheet-like bodies into country rocks (previously deformed and metamorphosed during a top-to-the-N–NNE Alpine orogeny) along a ductile extensional shear zone, located between orthogneisses and metasediments, which was possibly active during emplacement. The data presently available indicate that emplacement and associated ductile extensional deformation occurred during Late Oligocene–Early Miocene time. These results confirm previous contentions that there are Tertiary granites in this part of the Menderes Massif.     

基于强度折减概念的滑坡稳定性三维分析方法(I)：滑带土抗剪强度参数反演分析

滑带土抗剪强度是滑坡稳定性分析和防治工程设计中十分重要而又难于确定的参数之一。因此,基于临界状态假定的二维反分析方法得到了广泛应用。但是,自然界发生的滑坡基本上呈三维形态,其主滑方向有时变化也较大,使得有必要研究一种滑带土抗剪强度的三维反分析方法和滑坡稳定性的三维评价方法。笔者建议了一种基于强度折减概念的滑带土抗剪强度反分析方法,即通过逐步折减滑动面的强度参数,使滑动面的塑性区完全贯通,此时,塌滑体处于极限状态,所用强度参数即为滑带土的平均抗剪强度参数。从洪家渡水电站1#塌滑体计算成果来看,反演的滑带土摩擦角较二维反演值低4.1?,反映了滑坡体的三维效应,验证了所建议方法的可行性。     

北京怀柔HR_（88－1）钻孔剖面磁性地层学研究

在系统古地磁样品采集、处理和测量的基础上，运用磁性地层学的研究方法，对北京怀柔地区ＨＲ（８８－１）钻孔剖面进行了详细地层划分，分别确定了该区上新统、下更新统、中更新统和上更新统的分布深度及地质年代。     

A wavelet-based multifractal analysis of seismic data for facies identification. Application on the pilot KTB borehole

The main goal of this paper is to identify reflection from seismic data using the multifractal formalism. Firstly, the wavelet transform modulus maxima lines method is applied with a sliding window of 128 samples at the seismic seismogram data. After that, we estimate the generalized fractal dimension. Application at the noisy synthetic seismic seismogram of the pilot Kontinentales Tiefbohrprogramm de Bundesreplik Deutschland borehole shows that the three fractal dimensions related to the three first moments are a good tool that can separate between reflection dues to the change of facies and random noise.     

北京怀柔HR_（88－1）钻孔剖面磁性地层学研究

在系统古地磁样品采集、处理和测量的基础上，运用磁性地层学的研究方法，对北京怀柔地区ＨＲ（８８－１）钻孔剖面进行了详细地层划分，分别确定了该区上新统、下更新统、中更新统和上更新统的分布深度及地质年代。     

Palynostratigraphy of the Lower-Middle Jurassic deposits,borehole section Vostok 4 (Southeast of West Siberia)

This work presents the results of palynological investigation of the Vostok 4 borehole section situated in the Azharma region of the Ob-Irtysh facies area, where drilling has penetrated through the Urmanskaya, Ilansk, Peshkovskaya, and Tyumen formations. Six palynoassemblages are distinguished in the section based on the analyzed distribution of spores, pollen of terrestrial plants, and microphytoplankton. According to their succession, the section is subdivided into biostratigraphic units ranked as beds with palynomorphs. Comparative analysis and correlation with the Siberian palynostratigraphic standard scale of the Lower-Middle Jurassic, where succession of palynoassemblages is coordinated with ammonite zones, substantiate the Pliensbachian-Bajocian age of the deposits studied. Diverse microphytoplankton (dinoflagellate cysts, acritarchs, prasinophytes, zignematacean and colonial algae) occurs throughout the section. The facies environment of sedimentation is reconstructed based on quantitative proportions of microphytoplankton taxa.     

Thermal instability of the fluid column in a borehole: application to the Yaxcopoil hole (Mexico)

Observational evidence proved that even when a borehole is in “fully” stabilized conditions, temperature data may exhibit certain unrest resembling irregular oscillations in the order of hundredths or (in the extreme case) even tenths of degree. Temperature was monitored in complicated hydrogeological conditions in the Yaxcopoil-1 hole (Chicxulub impact structure, Mexico). Two experiments are reported: (a) 20-day monitoring when a logger was located in the center of the high temperature gradient anomaly produced by the cold wave slowly propagating downwards and (b) simultaneous three-loggers 18-day monitoring with loggers located above, in and below the anomaly. All observed temperature–time series displayed intermittent oscillations of temperature with sharp gradients and large fluctuations over all observed time scales. While the “upper” and “lower” records revealed quasi-periodic temperature variations, the “central” record shows fast temperature oscillations with strong up-and-down reversals, all with amplitudes up to a few tenths of degree. The observed temperature–time series were processed by recurrence and recurrence interval quantification as well as by spectral analyses. It is shown that fluid in a borehole, subject to thermal gradient, is stable, as far as the gradient remains below a certain critical value. At higher Rayleigh numbers, the periodic character of oscillations typical for “quiescent” regime is superseded by stochastic features. This “oscillatory” convection occurs due to instability of the horizontal boundary layers. In the specific case of the Yaxcopoil hole, the time series above and below the cold wave (characterized by relatively lower temperature gradients between 20 and 50 mK/m) contain a clear low frequency component produced by tidal forcing. This component dominates over the high frequency domain (periods from 10–15 to 1 min), which exhibit a scaling behavior. This pattern conspicuously changes in the center part of the cold wave, where the local temperature gradient exceeds 200 mK/m and where tidal forcing composes only ~3% of the signal.     

中国大陆科学钻探主孔中磷灰石的磁黄铁矿出溶结构

在中国大陆科学钻探主孔中部的榴辉岩样品B1021R642P40a、B1039R646P47a、B1046R648P4c和B1053R649P74k中,我们发现了磷灰石的磁黄铁矿出溶结构.磷灰石是该榴辉岩的主要副矿物,其自形程度较高,与石榴石共生.样品中几乎所有磷灰石均发育出溶结构,至少存在两组相互垂直的出溶棒.出溶棒形状规则,一样宽(＜1μm),但长度变化大(5～50μm).利用高分辨能谱仪测定表明,出溶棒主要由Fe和S两种元素组成.由于还不能准确地确定其Fe/S比值,初步确定其为磁黄铁矿(Fe1-xS).磷灰石由于含大量稀土元素和挥发性组分如OH、F、Cl和S,它的深循环因此可能对地球的水、硫以及其它挥发性组分的全球平衡具有重要影响.