The Selection of Field Acquisition Parameters for Dispersion Images from Multichannel Surface Wave Data

The accuracy and resolution of surface wave dispersion results depend on the parameters used for acquiring data in the field. The optimized field parameters for acquiring multichannel analysis of surface wave (MASW) dispersion images can be determined if preliminary information on the phase velocity range and interface depth is available. In a case study on a fill slope in Hong Kong, the optimal acquisition parameters were first determined from a preliminary seismic survey prior to a MASW survey. Field tests using different sets of receiver distances and array lengths showed that the most consistent and useful dispersion images were obtained from the optimal acquisition parameters predicted. The inverted S-wave velocities from the dispersion curve obtained at the optimal offset distance range also agreed with those obtained by using direct refraction survey.     

Rayleigh-Wave Dispersive Energy Imaging Using a High-Resolution Linear Radon Transform

Multichannel Analysis of Surface Waves (MASW) analysis is an efficient tool to obtain the vertical shear-wave profile. One of the key steps in the MASW method is to generate an image of dispersive energy in the frequency-velocity domain, so dispersion curves can be determined by picking peaks of dispersion energy. In this paper, we propose to image Rayleigh-wave dispersive energy by high-resolution linear Radon transform (LRT). The shot gather is first transformed along the time direction to the frequency domain and then the Rayleigh-wave dispersive energy can be imaged by high-resolution LRT using a weighted preconditioned conjugate gradient algorithm. Synthetic data with a set of linear events are presented to show the process of generating dispersive energy. Results of synthetic and real-world examples demonstrate that, compared with the slant stacking algorithm, high-resolution LRT can improve the resolution of images of dispersion energy by more than 50%.     

Experimental and numerical analysis of MASW tests for detection of buried timber trestles

This paper presents results from multi-channel analysis surface waves (MASW) tests conducted to locate buried timber trestles in two different sections (A and B) of an earth embankment. For section A, the location of the trestles is known as well as the soil properties; thus, it is used for calibration purposes. Conversely, the location of the timber trestles is unknown for section B. A seismic array of 24 geophones with a spacing of 0.5 m is used for surface-wave measurements. Different signal processing techniques are used for data analysis: dispersion curves, power spectral functions, frequency-spectra contour plots, two-dimensional-Fourier transform, and the wavelet transform. A new procedure is proposed for the surface location of buried trestles, which is based on the use of the normalized average power energy plot. Finite-element numerical simulations of MASW tests on layered and homogeneous media with and without buried trestles are performed to support experimental results and to explain the wave–trestle interaction. The numerical simulations show that a buried trestle induces vibration amplifications at the surface in front of its location but vibration attenuation immediately after. These effects, however, are observed only if the embedment depth of timber trestle is smaller than one third of the wavelength. Experimental and numerical results show that the results from MASW tests can be successfully used to define the surface location of decayed buried trestles.     

InterPACIFIC project: Comparison of invasive and non-invasive methods for seismic site characterization. Part II: Inter-comparison between surface-wave and borehole methods

The InterPACIFIC project was aimed at assessing the reliability, resolution, and variability of geophysical methods in estimating the shear-wave velocity profile for seismic ground response analyses. Three different subsoil conditions, which can be broadly defined as soft-soil, stiff-soil, and hard-rock, were investigated. At each site, several participants performed and interpreted invasive measurements of shear wave velocity (Vs) and compression wave velocity (Vp) in the same boreholes. Additionally, participants in the project analysed a common surface-wave dataset using their preferred strategies for processing and inversion to obtain Vs profiles. The most significant difference between the invasive borehole methods and non-invasive surface wave methods is related to resolution of thin layers and abrupt contrasts, which is inherently better for invasive methods. However, similar variability is observed in the estimated invasive and non-invasive Vs profiles, underscoring the need to account for such uncertainty in site response studies. V_S,30 estimates are comparable between invasive and non-invasive methods, confirming that the higher resolution provided by invasive methods is quite irrelevant for computing this parameter.     

基于矢量波数变换法(VWTM)的多道Rayleigh波分析方法

在近二十年来,多道面波分析法（MASW）由于其便捷、高效等特性在浅层地震勘探领域得到了广泛的应用.本文基于多道面波勘探的采集方式,提出了一种新的面波多道分析方法——矢量波数变换法（VWTM）.该方法通过对震源的近似,基于水平层状模型得到台站与震源间近似格林函数,然后进行矢量波数变换得到含有高阶模态Rayleigh波（频率-相速度）频散能量图.本研究首先利用合成地震数据到频散能量图与理论频散曲线进行叠加分析该方法的有效性和正确性;然后与相移法进行对比分析,我们发现在频散能量图中VWTM法对基阶、高阶模态成像均具有更高的分辨率和成像质量;最后我们将其应用于实际多道瞬态面波探测中,通过与相移法进行对比分析,发现VWTM法是一种方便、实用、有效的Rayleigh波频散提取方法.VWTM法提取多模态的Rayleigh波频散特征具有巨大潜力,可为基阶、高阶面波频散联合反演提供丰富的高阶模态频散信息.

     

Field testing and analysis of high speed rail vibrations

This paper outlines an experimental analysis of ground-borne vibration levels generated by high speed rail lines on various earthwork profiles (at-grade, embankment, cutting and overpass). It also serves to provide access to a dataset of experimental measurements, freely available for download by other researchers working in the area of railway vibration (e.g. for further investigation and/or the validation of vibration prediction models).First, the work outlines experimental investigations undertaken on the Belgian high speed rail network to investigate the vibration propagation characteristics of three different embankment conditions. The sites consist of a 5.5 m high embankment, an at-grade section and a 7.2 m deep cutting. The soil material properties of each site are determined using a ‘Multichannel Analysis of Surface Waves’ technique and verified using refraction analysis. It is shown that all sites have relatively similar material properties thus enabling a generalised comparison.Vibration levels are measured in three directions, up to 100 m from the track due to three different train types (Eurostar, TGV and Thalys) and then analysed statistically. It is found that contrary to commonly accepted theory, vertical vibrations are not always the most dominant, and that horizontal vibrations should also be considered, particularly at larger offsets. It is also found that the embankment earthworks profile produced the lowest vibration levels and the cutting produced the highest. Furthermore, a low (positive) correlation between train speed and vibration levels was found. A selection of the results can be downloaded from www.davidpconnolly.com.     

基于自动安置排列的多道面波分析方法

横波速度由于更能直接反映岩石的物理性质,从而在许多工程、环境和地下水勘查中有重要作用.多道面波分析方法(MASW)是一种新技术,通过求得的一维近地表横波速度剖面构建一个二维横波速度场,从而准确探测近地表介质情况.针对该方法数据的采集,提出了一种检波器排列自动安置的技术(自动安置排列),即使用牵引车辆的液压驱动装置在几秒内自动安置几十个检波器,并将其与传统安置排列的方法做了比较,结果表明,自动安置排列技术可用于多道面波分析方法,而且可以大大减少多道面波分析方法的采集时间和费用.     

Research on the middle-of-receiver-spread assumption of the MASW method

The multichannel analysis of surface wave (MASW) method has been effectively used to determine near-surface shear- (S-) wave velocity. Estimating the S-wave velocity profile from Rayleigh-wave measurements is straightforward. A three-step process is required to obtain S-wave velocity profiles: acquisition of a multiple number of multichannel records along a linear survey line by use of the roll-along mode, extraction of dispersion curves of Rayleigh waves, and inversion of dispersion curves for an S-wave velocity profile for each shot gather. A pseudo-2D S-wave velocity section can be generated by aligning 1D S-wave velocity models. In this process, it is very important to understand where the inverted 1D S-wave velocity profile should be located: the midpoint of each spread (a middle-of-receiver-spread assumption) or somewhere between the source and the last receiver. In other words, the extracted dispersion curve is determined by the geophysical structure within the geophone spread or strongly affected by the source geophysical structure. In this paper, dispersion curves of synthetic datasets and a real-world example are calculated by fixing the receiver spread and changing the source location. Results demonstrate that the dispersion curves are mainly determined by structures within a receiver spread.     

SASW及MASW方法在隐伏断层探测中的应用

针对地壳浅部介质横向变化大的特点,用瞬态瑞利波SASW与MASW方法对河北夏垫断裂进行了探测与数据处理分析.分别用时间域互相关法和频率域f-k分析法提取频散曲线,然后进行反演得到横波速度结构.实验结果表明瞬态瑞利波法在应用中便捷、灵活,对于探测地表介质中非均匀异常体及断裂向浅部的延伸情况具有独特的应用前景.     

埋入源多道面波分析(MASW)中最小偏移距的估计方法

多道面波分析（MASW）法是一种被广泛使用的浅层地震勘探方法.为解决埋入源近场效应对MASW法应用的影响,本文分析了埋入源产生的Rayleigh波传播机制,探讨了MASW法的排列参数对地震记录的影响,提出了确定最小偏移距的经验公式.通过对实际地质模型的有限元模拟,验证了经验公式的合理性.在以经验公式为指导的野外实测中,利用多种方法提取了相对可靠的频散曲线,采用基阶和高阶面波联合反演,所得的一维速度结构与钻孔资料具有很强的相关性,表明本文发展的最小偏移距估计方法具有一定的实际应用价值.