The Correlation Bias for Two-Dimensional Simulations by Turning Bands

The turning bands method (TBM) generates realizations of isotropic Gaussian random fields by summing contributions from line processes. We consider two-dimensional simulations and study the correlation bias attributable to the use of only a finite number L of lines. Our analytical and numerical results confirm that the maximal bias is of order 1/L, and that L = 64 lines suffice for excellent covariance reproduction. The notorious banding observed in simulations with an insufficient number of lines is a related but different phenomenon and depends strongly on the choice of the line simulation technique. Clear-cut recommendations for the number of lines necessary to avoid the effect can only be based on practical experience with the specific code at hand.     

Modeling the seismic response of basin-edge structure by a sequential waveform method

A sequential waveform method is developed to simulate the seismic response of basin-edge structure excited by a plane incident P-wave. The full procedure involves: (a) a previous parameterization of the investigated model using the seismic wave velocities and depths of the sedimentary stratifications; (b) an input motion determined from the records at stations installed on hard rock; (c) forward computation of the P-SV elastic wave field by means of a two-dimensional finite difference (FD) method; (d) the optimization of the model vector using simulated annealing technique and comparing the simulated seismic response of the tested structure with the observed wave field; (e) the correction of the initial model by trial-and-error by testing the differences between synthetics and observed data, and (f) the final solution obtained by iteration using the conjugate gradient algorithm. The search of an optimal basin-edge model has been parallel processed by varying the shapes and velocities of strata on the basis of the fitting of relative timing, amplitude and phase between the output and the observed data. The input motion and sensitivity have been checked and the validity of the method has been demonstrated by numeric analysis. Using the teleseismic records generated by 7 earthquakes recorded at 26 broadband seismic stations, we have studied the seismic velocity structure of the southern edge of the Jiyang depression located in the Bohai Bay basin, northern China. Two cross sections show an agreement between the velocity results and the geological sections available in the region. In addition, we obtain evidence of three hidden faults under the sections and features that suggest major extensions at the Paleogene.     

GPS坐标向国家坐标转换的三维分离回归法

三维分离回归法是一种简单、有效、实用的转换方法,该方法可有效地克服病态矩阵问题。同时,为切实、有效地提高三维分离回归法的转换精度,计算时引入了三向尺度因子,使得三维转换参数由传统的7个变为现在的9个。详细介绍了三维分离回归法的基本原理、转换过程及转换实例。     

General elastic analysis of piles and pile groups

This paper describes the development of a boundary element analysis for the behaviour of single piles and pile groups subjected to general three‐dimensional loading and to vertical and lateral ground movements. Each pile is discretized into a series of cylindrical elements, each of which is divided into several sub‐elements. Compatibility of vertical, lateral and rotational movements is imposed in order to obtain the necessary equations for the pile response. Via hierarchical structures, 12 non‐zero sub‐matrices in a global matrix are derived for the basic influence factors. Solutions are presented for a series of cases involving single piles and pile groups. In each case, the solutions are compared with those from more simplified existing pile analyses such as those developed by Randolph and by Poulos. It is shown that for direct loading effects (e.g. the settlement of piles due to vertical loading), the simplified analyses work well. However, for ‘off‐line’ response (such as the lateral movement due to vertical loading) the differences are greater, and it is believed that the present analysis gives more reliable estimates. Copyright © 2000 John Wiley & Sons, Ltd.     

Tests for individual Sulfate－Containing Particles in Urban Atmosphere in Beijing

Thin film methods and X ray energy dispersive technique were applied to analyze sulfate-containing particles in Beijing in order to examine their features and sources. Atmospheric aerosol particles were collected on electron mi-croscope meshes according to two size ranges: coarse particles (r>0.5μm) and fine particles (0.5μm≥r≥0.1μm) by using a two-stage impactor. It was found fiat more than seventy percent of the fine particles and about twenty percent of the coarse particles were sulfate-containing particles. These particles were formed mainly through heterogeneous nucleation. The element composition analyses revealed that the atmospheric aerosol particles in Beijing were domi-nated by crustal particles and construction dust.     

三分量地震资料中各向异性检测

各向异性研究是当令地震学研究领域中重要课题之一；三分量地震资料中各向异性的检测是各向异性理论研究成果解决地球科学实际问题的重要桥梁。本文简要描述了各向异性介质中横波分裂现象，分别介绍了现有的四种主要检测技术，即偏振图法、协方差拒阵法、质，点振动分辨率法及传输矩阵法，并对这四种技术作了一定的评述。     

中国省会城市国际化水平比较研究

城市国际化不仅是一个结果更是一个与其他国际城市逐步接轨的过程,在此过程中,通过与其他城市的物质、文化与信息的交流,实现城市发展利益的最大化。在目前城市国际化比较研究的基础上,针对现有方法的不足,运用因子分析法,进行了分因素排名比较分析和综合得分排名的分类比较分析,最后根据综合得分通过类间距法将所有省会城市分为三类,并提出各类城市在不同城市国际化发展阶段应选择不同的发展策略。     

CHANGES OF RIVER BED PATTERN OF A LOWLAND RIVER: EFFECT OF NATURAL PROCESSES OR ANTHROPOGENIC INTERVENTION?

GPR and aerial surveys were conducted to study changes of channel pattern in the lower course of the Obra River (western Poland). The river is an example of an intensive anthropogenic transformation, however, the origin of the river pattern changes in its lower course is not obvious. The GPR measurements were done using a georadar MALÅ ProEx equipped with a shielded 250 MHz antenna. A 3D analysis of the GPR data supported with lithologic information indicated traces of a multi‐channel pattern. A variable orientation of sediment layering within channel bars and differences in channels depth and width pointed to changes of direction of the river bed migration. Analysis of aerial photographs and a satellite image indicated that only a few of the channels inferred from GPR could be discerned. The reason could be the more than 1 m thick fine sands layer covering all the alluvial structures. Analysis of historical maps from the eighteenth and the nineteenth centuries showed that 250 years ago the Obra was a meandering river. The maps illustrate also several meander cutoffs and decreased wetlands surface. The following transformations of the river bed pattern were discerned: 1. From braided to meandering channel pattern which could be a natural process caused by climatic and sediment transport rate changes that was also observed in case of other lowland rivers. 2. From meandering to sinuous pattern with channel islands and then to sinuous with oxbow lakes. However, further research is needed to study reasons and timing of the observed changes.     

An application of three-dimensional electrical resistivity imaging for the detection of an underground waste-water system

A 3D electrical resistivity imaging survey is presented in this paper. The objective was to investigate an underground wastewater system at the University of Malaya, Malaysia. Apparent resistivity data were collected along ten parallel lines using a Wenner-Schlumberger configuration; electrode cables were oriented in the x-direction with 3 m spacing. Roll-along measurements using a line spacing of 3 m were carried out covering a grid of 20 × 10 electrodes. All data sets were merged into a single data file in order to perform a 3D inversion. Two different 3D least squares algorithms, based on the robust inversion method and the smoothness-constrained technique, were used for the inversion of the apparent resistivity data. Both the horizontal and vertical extents of the anomalous zones found by inversion are displayed. The results indicate the superiority of the robust inversion method over the smoothness-constrained technique at this site. The results are in sufficient accordance with previously known information about the investigation area. The results show that 3D electrical resistivity imaging surveys, in combination with an appropriate 3D inversion method, can be highly useful for engineering and archaeological investigations as well as for environmental applications.