陕西小秦岭地区的环形构造及其控矿作用探讨

本文运用波浪镶嵌构造观点研究小秦岭地区发育着的许多大小不等的环形构造。它与区域北东向、东西向构造相互交织形成的网格构造相互套合,共同组成了该区的复杂构造形态。环形构造对矿产、尤其对同生金属矿产起着明显的控制作用,研究环形构造,将对矿产的普查勘探及成矿预测起到一定的作用,     

A gradient method for interpreting magnetic anomalies due to horizontal circular cylinders,infinite dykes and vertical steps

A new method of interpreting magnetic anomalies of arbitrarily-magnetised horizontal circular cylinders, dipping dykes and vertical steps is presented. The method makes use of both horizontal and vertical gradients of the magnetic field of the model under consideration, rather than the observed magnetic anomaly. Vertical and horizontal gradients are calculated from the observed anomalies, and plotted one against the other to find out the locus of tip of the resultant gradient vector. This locus is a symmetrical curve for each of the three models mentioned above. The properties of these curves are used to deduce the various parameters of these models and the direction of magnetisation.     

[1H] and [13C]NMR studies on the importance of aromatic structures in fulvic and humic acids

To obtain information on the contribution of aromatic fragments to the chemical structure of humic substances, we carried out a study on the [¹H]NMR and [¹³C]NMR spectra of humic and fulvic acids and their oxidative degradation products extracted from an Andosol soil.[¹H]NMR spectra of all organic fractions present considerable adsorption between 7.4 and 8.8 ppm, due to the presence of aromatic protons.The percentages of aromatic protons in respect to the total amount of protons are as follows: FA 20%, HA 19%, degraded FA < 12%, degraded HA 14%. The values indicate that the contribution of aromatic structures to the humic substances is significant, also considering that they are highly substituted.The degraded fractions contain smaller amounts of aromatic protons, because degradation causes the opening of the aromatic rings. Thus results obtained from the degradation do not seem to be reliable for defining the importance of aromatic structures in humic substances.Also the [¹³C]NMR spectra show signals in the aromatic region which derive from unsubstituted carbon atoms, while signals originating from tertiary carbon atoms merge with the noise. We believe that, at present, [¹H]NMR spectroscopy is more suited for studying the role played by aromatic compounds in organic soil fractions.     

关于中国陆架沙漠化理论几个问题的探讨

陆架沙漠化理论主要有两方面的问题;第一,该理论所例举的沙漠化证据大多属于不能确认沙漠环境的多解标志;第二,该理论没有阐明冰后期海进过程对陆架上可能存在的风成沙所产生的影响。本文就这些问题进行了讨论,认为中国大陆架上的残留沉积不宜定为古沙漠堆积。     

Scattering of SH-wave by multiple circular cavities in half space

In this paper, an analytic method is developed to address steady SH-wave scattering and perform dynamic analysis of multiple circular cavities in half space. The scattered wave function used for scattering of SH-waves by multiple circular cavities, which automatically satisfies the stress-free condition at the horizontal surface, is constructed by applying the symmetry of the SH-wave scattering and the method of multi-polar coordinates system. Applying this scattered wave function and method of moving coordinates, the original problem can be transformed to the problem of SH-wave scattering by multiple circular cavities in the full space. Finally, the solution of the problem can be reduced to a series of algebraic equations and solved numerically by truncating the infinite algebraic equations to the finite ones. Numerical examples are provided for case with two cavities to show the effect of wave number, and the distances between the centers of the cavities and from the centers to the ground surface on the dynamic stress concentration around the cavity impacted by incident steady SH-wave.     

A warning system for rainfall-induced shallow failures

It is widely recognised that soil slips and debris flows are triggered by short intense storms. Owing its geologic, geomorphologic and climatic settings, the Piedmont Region (NW Italy) is highly prone to the occurrence of this kind of landslides. In the last two centuries, in fact, a total of 105 severe meteoric events which triggered shallow failures occurred and, of these, 18 events took place from 1990 to 2002. A fair number of rainfall thresholds have been proposed in the literature, defined both on empirical or on physical bases. Empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides, while physical thresholds are based on numerical models that consider the relation between rainfall, pore pressure and slope stability. The main objective of this paper is the identification of the empirical triggering thresholds for the Piedmont Region. Four meteoric events were selected and analysed (November 4–5, 1994; July 7–8, 1996; April 27–30, 2000; October 13–16, 2000) because they supply a wide range of variation for both rainfall parameters (duration, intensity, cumulative rainfalls) and the number of induced landslides. In the intensity–duration plot, the critical limit is described by the equation: I=19D^−0.50 (where I=rainfall intensity expressed in mm/h and D=rainfall duration expressed in hours). Such a limit is traced to envelop 90% of the points on the graph. In the NI–D diagram the triggering thresholds are given by the equations NI=0.76D^−0.33 and NI=4.62D^−0.79 (where NI=normalised intensity with respect to the annual precipitation, MAP, expressed in %, [(mm/h)/PMA]×100). In the article the different meaning of these thresholds is discussed. Finally, the diagram NI–NCR is proposed; the triggering threshold is given by the expression: NI=−0.09ln[NCR]+0.54 (where NCR is the normalised cumulative critical rainfall, [mm/PMA]×100). The application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide-prone areas is discussed. In detail an operating procedure which is presently being verified and tested in the studied area is described.     

Landslides triggered by the 23 November 2000 rainfall event in the Imperia Province, Western Liguria, Italy

From mid-October to 22 November 2000, the western Liguria Region of Italy experienced prolonged and intense rainfall, with cumulative values exceeding 1000 mm in 45 days. The severe rainfall sequence ended on November 23 with a high-intensity storm that dumped more than 180 mm of rain in 24 h. The high-intensity event caused flooding and triggered more than 1000 soils slips and debris flows and a few large, complex landslides. Slope failures caused three fatalities and severe damage to roads, private homes, and agriculture. Large (1:13,000) and very large (1:5000) scale colour aerial photographs were taken 45 days after the event over the areas most affected by the landslides. Through the interpretation of the 334 photographs covering an area of 500 km², we prepared a landslide inventory map that shows 1204 landslides, for a total landslide area of 1.6 km². We identified the rainfall conditions that triggered landslides in the Armea valley using cumulative- and continuous-rainfall data, combined with detailed information on the time of landslide occurrence. Landslide activity initiated 8 to 10 h after the beginning of the storm, and the most abundant activity occurred in response to rainfall intensities of 8 to 10 mm per hour. For the Ceriana Municipality, an area where the landslides were numerous in November 2000, we also collected information about a historical event that occurred on 8–11 December 1910 and triggered abundant landslides resulting in severe economic damage. A comparison of the damage caused by the historical and the recent landslide events indicated that damage caused by the 1910 historical event was more diffused but less costly than the damage caused by the 2000 event.     

关于GIS缓冲区的建立问题

在对多种方法编程实践的基础上，本文对绘制平行曲线特别是形成缓冲区的两种主要方法（角分线法与圆弧法）进行了分析对比。角分线法带来很多异常情况，连同其补充校正措施，该方法就失去其相对简易性。相反，圆弧法是在强化判断（凸凹判断和弦弧可控逼近）的基础上，最大限度地确保双线的等宽性。文中提出二重数学模型：形成双线的几何算法模型和针对自相交问题的关系处理模型。除了重点对单一目标进行研讨外，文末对具有集合特征的树结构和网结构的缓冲区建立问题也进行了原则性讨论。     

地下圆曲线标定过程中合理弦长与边垂距的确定

根据地下圆曲线所片位置的特殊性，提出了确定合理弦长进进行地下圆曲线标定的方法，导出了计算弦线上任一点的内、外边垂的距的公式，有利于保证测角测边精度施工的进度和质量。