Embankment deformation analyzed by elastoplastic damage model coupling consolidation theory

The deformation, of embankment has serious influences on neighboring structure and infrastructure. A trial embankment is reanalyzed by elastoplastic damage model coupling Blot＇ s consolidation theory. With the increase in time of loading, the damage accumulation becomes larger. Under the centre and toe of embankment, damage becomes serious. Under the centre of embankment, vertical damage values are bigger than horizontal ones. Under the toe of embankment, horizontal damage values are bigger than vertical ones.     

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Partial derivatives of surface wave phase velocities for flat anisotropic models

Summary. Surface wave behaviour in flat anisotropic structures is first illustrated by performing an exact computation on a simple two-layer model. The variational procedure of Smith & Dahlen is then used to compute the partial derivatives of surface wave phase velocities with respect to the elastic parameters in more realistic earth models. Linear relationships between the partial derivatives for a general anisotropic structure and those for a transversely isotropic structure are derived. When considering waves propagating in a fixed direction, there are only four independent derivatives for Rayleigh waves, and two for Love waves. To avoid the lack of resolution in an inverse method, we propose to use physically constrained models. These results are illustrated by using a model with hexagonal symmetry and a symmetry axis oriented either vertically or horizontally. Quasi-Love- and quasi-Rayleigh-wave partial derivatives are computed for both axis orientations. Modes up to the second overtone and periods ranging between 45 and 130 s have been considered. Finally, anomalies of phase velocity are computed in an oceanic model made of 1/6 oriented olivine crystals with horizontal or vertical preferred orientations of the a -axis.     

Three-dimensional image of the anisotropic bodies beneath central Honshu, Japan

Shear-wave splitting from local deep earthquakes is investigated to clarify the volume and the location of two anisotropic bodies in the mantle wedge beneath central Honshu, Japan. We observe a spatial variation in splitting parameters depending on the combination of sources and receivers, nearly N–S fast in the northern region, nearly E–W fast in the southern region and small time delays in the eastern region. Using forward modelling, two models with 30 and 10 per cent anisotropy are tested by means of a global search for the locations of anisotropic bodies with various volumes. The optimum model is obtained for 30 per cent anisotropy, which means a 5 per cent velocity difference between fast and slow polarized waves. The northern anisotropic body has a volume of 1.00° (longitude) × 0.5° (latitude) × 75 km (depth), with the orientation of the symmetry axis being N20°E. The southern anisotropic body has a volume of 1.25° × 1.25° × 100 km with the symmetry axis along N95°E. Our results show that the anisotropic bodies are located in low-velocity and low- Q regions of the mantle. This, together with petrological data and the location of volcanoes in the arc, suggests that the possible cause of the anisotropy is the preferred alignment of cracks filled with melt.     

中国大陆水平地壳运动的数学模型

在获得中国区域1000个实测GPS台站速度场的基础上,利用多面函数法、滑动欧拉矢量法和滑动弹塑性模型法建立了中国大陆水平地壳运动模型,统计表明3种方法外部符合精度2～4mm/a,模型互差精度约为3mm/a。     

Small sized charophyte gyrogonites in the Maastrichtian of Coll de Nargó, Eastern Pyrenees: An adaptation to temporary floodplain ponds

Charophytes bearing small sized fructifications dominated in fluviatile floodplain facies (red beds) from the Maastrichtian of Coll de Nargó and neighbouring basins in the southern Pyrenees (Catalonia, Spain). These charophytes mainly belong to the genus Microchara and are often disregarded in biostratigraphic studies, which focus their attention instead on facies from permanent lakes that are richer in species which usually bear fructifications with a larger size range. However, small sized gyrogonites are also significant for biostratigraphic purposes and even include some of the index species for Maastrichtian biozones in Europe. Indeed, the charophyte assemblages from the Maastrichtian of Coll de Nargó belong to the Microchara punctata biozone, recently calibrated to the middle-upper Maastrichtian.Floodplain ponds from the Maastrichtian red beds of Coll de Nargó (Lower Red Unit) were extremely shallow, received considerable terrigenous influx and were frequently exposed, probably resulting in turbid, warm waters with high light availability. These conditions could explain the almost exclusive occurrence of charophytes with small fructifications in the Lower Red Unit. The available data, mainly based on oospores from extant species, indicate that the small size observed in gyrogonites from temporary ponds may represent an adaptation to environmental stress. Fossil species with small gyrogonites of Microchara cristata, M. punctata and Microchara nana would thus develop massively in stressed shallow ponds on fluvial floodplains. To contrast these hypotheses, we compared our results to those of four well-known case studies with similar sedimentological contexts, ranging from the Lower Cretaceous to the upper Eocene–lower Oligocene. Gyrogonite size patterns were similar in all cases, possibly suggesting that characeans display a long history of adaptation to shallow, temporary and turbid floodplain ponds by means of producing a high number of small gyrogonites, probably representing short life cycles and opportunistic strategies.     

兰天武地区现今大地垂直形变场演化与地壳运动特征

用分段线性速率整体动态平差法处理了兰天武地区２０多年来的多期水准资料，分析了该区现今大地垂直形变场演化与地壳运动特征。研究结果表明：该区垂直形变七十年代曾表现出山间盆地大幅度上升的强烈逆继承性运动；八十年代华家岭等两北部山地上升、东南部盆地下沉的继承性运动增强；而目前基本恢复了正常的继承性运动状态。进一步分析认为：强烈逆继承性运动和继承性运动增强是区域应力场趋于强化的标志；正常继承性运动的恢复可能是应力场调整的结果。     

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中国大陆地壳运动与强震关系研究

利用GPS观测结果研究了中国大陆当前地壳运动的空间分布及其所揭示的大区域构造变形背景与趋势;讨论了区域水平运动、应变率场分布与强震地点的关系;通过对昆仑山口西Ms8.1等地震区域水平运动与形变的分析,研究了强震过程的区域形变场变化的主要特征;提出了识别孕震形变场以进行中长期强震地点预测的思路和途径。