On the Incorporation of the Effect of Crustal Structure into Empirical Strong Ground Motion Estimation

This article has two purposes. Firstly, a validation exercise of the modal summation technique for the computation of synthetic strong-motion records is performed for two regions of Europe (Umbria-Marche and south Iceland), using a variety of region specific crustal structure models, by comparing the predicted ground motion amplitudes with observed motions. It is found that the rate of decay of ground motions is well predicted by the theoretical decay curves but that the absolute size of the ground motions is underpredicted by the synthetic time-histories. This is thought to be due to the presence of low-velocity surface layers that amplify the ground motions but are not included in the crustal structure models used to compute the synthetic time-histories. Secondly, a new distance metric based on the computed theoretical decay curves is introduced which should have the ability to model the complex decay of strong ground motions. The ability of this new distance metric to reduce the associated scatter in empirically derived equations for the estimation of strong ground motions is tested. It is found that it does not lead to a reduction in the scatter but this is thought to be due to the use of crustal structure models that are not accurate or detailed enough for the regions studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fractally Invariant Distributions and an Application in Geochemical Exploration

Fractal modelling has been applied extensively as a means of characterizing the spatial distribution of geological phenomena that display self-similarity at differing scales of measurement. A fractal distribution exists where the number of objects exhibiting values larger than a specified magnitude displays a power-law dependence on that magnitude, and where this relationship is scale-invariant. This paper shows that a number of distributions, including power-function, Pareto, log-normal and Zipf, display fractal properties under certain conditions and that this may be used as the mathematical basis for developing fractal models for data exhibiting such distributions. Population limits, derived from fractal modelling using a summation method, are compared with those derived from more conventional probability plot modelling of stream sediment geochemical data from north-eastern New South Wales. Despite some degree of subjectivity in determining the number of populations to use in the models, both the fractal and probability plot modelling have assisted in isolating anomalous observations in the geochemical data related to the occurrence of mineralisation or lithological differences between sub-catchments. Thresholds for the main background populations determined by the fractal model are similar to those established using probability plot modelling, however the summation method displays less capacity to separate out anomalous populations, especially where such populations display extensive overlap. This suggests, in the geochemical data example provided, that subtle differences in the population parameters may not significantly alter the fractal dimension.     

海底电缆鬼波压制及陷频补偿方法研究

受到海底、自由表面等强反射界面的影响, 在海底电缆采集的地震资料中鬼波干扰往往非常发育, 在频谱中表现为明显的陷频现象, 严重影响地震剖面的质量, 给后期的处理解释带来困难。为克服这一困难, 根据海底电缆双检(陆检和水检)对下行波场的不同响应, 在深入研究伪多道匹配滤波技术的基础上提出了伪多道双检合成方法。与传统的求取反射系数的双检合成方法不同, 该方法完全数据驱动。在合成数据和渤海地震资料的实际应用中, 鬼波成分得到了明显的压制, 同时拓宽频带, 补偿陷频, 证明了该方法的有效性。     

Complete synthetic seismograms for high-frequency multimodeSH-waves

We present an efficient scheme to compute high-frequency seismograms (up to 10 Hz) forSH-waves in a horizontally stratified medium with the mode summation method. The formalism which permits the computation of eigenvalues, eigenfunctions and related integral quantities is discussed in detail. Anelasticity is included in the model by using the variational method. Phase velocity, group velocity, energy integral and attenuation spectra of a structure enable the computation of complete strong motion seismograms, which are the basic tool for the interpretation of near-source broad-band data.Different examples computed for continental structures are discussed, where one example is the comparison between the observed transversal displacement recorded at station IVC for the November 4, Brawley 1976 earthquake and synthetic signals. In the case of a magnitudeM _L =5.7 earthquake in the Friuli seismic area we apply the mode summation method to infer from waveform modeling of all three components of motion of observed data some characteristics of the source.On leave from Institute of Geophysics, ETH, Zürich, Switzerland.     

桩端持力层加筋作用的特性探讨

运用弹性半空间无限体的明德林解答和浅基础中的分层总和法、桩土间滑动采用刚塑性模型，以某工程试桩资料为例，较详细地分析了桩端持力层加筋作用的特性。并通过工程实例证明本文研究结果是正确的，这对桩基的设计和研究有较大的参考价值。     

民房震害预测专家评定统计模型的探讨

本文针对专家评定意见有一定伸缩性的特点,将专家意见表示为评定论域上的模糊子集,利用可能性相加原理,对专家意见进行了统计分析,得出综合性的意见。结果表明,利用伸缩性提供的丰富信息,可以较好地总结专家意见。基于几种模型的仿真可靠性分析结果,本文推荐可靠性最高的模型作为城市平房震害预测统计手段。     

地裂缝场地施工降水对地表沉降和地层应力的影响研究

地裂缝是西安市典型的城市地质灾害，地下水位的变化是诱发地裂缝活动的重要因素。以西安地铁六号线暗挖段施工降水为研究背景，基于有限元数值模拟计算，分析了地裂缝场地施工降水引起的地表沉降规律和地层应力变化特征。计算结果表明:当地下水位下降时，地表沉降量上盘大于下盘，地裂缝带两侧地表存在差异沉降的现象，最大差异沉降量与地下水位下降深度近似呈直线关系；不同位置处地表的横向沉降呈现出"Z"形的变化特征，差异沉降区随地裂缝位置的变动而变化，且差异沉降量与横向地表位置近似呈二次函数曲线关系；地层竖向应力随着地下水位下降而增大，地裂缝位置处地层应力存在突变现象，上下盘应力影响区与地层深度近似呈三次函数曲线关系；基于分层总和法计算了地下水位下降时地表沉降量的解析解，并与数值模拟结果进行对比，发现两种方法计算结果基本一致，得到了计算地表最大沉降量的经验公式。研究结果可为地裂缝场地地铁隧道及其他地下工程安全施工提供科学指导。      

Meixner functions for derivation of the unit hydrograph

The Meixner functions are utilized to relate the effective rainfall, the direct runoff and the unit hydrograph through linkage equations. The linkage equations are then employed to derive the unit hydrograph for given rainfall-runoff data on a small agricultural watershed. These functions are tested with regard to their ability to reproduce and predict the direct runoff hydrograph. The Meixner functions are found to be an effective analytical tool for hydrograph synthesis. Further, they compare well with the least squares and linear programming methods of the unit hydrograph derivation.     

Discretization error for the superposition of Gaussian beams

Summary. A high-frequency asymptotic integral expansion of a time-harmonic wavefield into Gaussian beams was derived in a previous paper by Klimeš. The discretization error caused by replacing this integral superposition by a discrete summation of Gaussian beams is estimated in this paper.