共查询到20条相似文献，搜索用时 15 毫秒
1.
The dispersive characteristics of Rayleigh type surface waves were utilized to estimate shear wave velocity (Vs) profile followed by imaging the shallow subsurface granitic layers in the heart of Hyderabad. The reliability of Multichannel Analysis of Surface Waves (MASW) depends on the accurate determination of phase velocities for horizontally traveling fundamental mode Rayleigh waves. Multichannel recording leads to effective identification and isolation of various factors of noise. Calculating the 1-D shear wave velocity (Vs) field from surface waves ensures high degree of accuracy irrespective of cultural noise. The main advantage of mapping the bed rock surface with shear wave velocity (Vs) is the insensitivity of MASW to velocity inversion besides being free from many constraints such as contrast in physical properties etc. Modeling of surface waves data results a shear wave velocity (Vs) of 250?C750 m/s covering the top soil to weathering and up to bedrock corresponding to a depth range of 10?C30 m. Further, the computed N values (which is an indicator of site characteristic) based on the harmonic shear wave velocity up to a depth of 5 m is found to be quite high (> 25?C30) well above 5 indicating the site to be safe and strong enough and not prone to liquefaction. A pair of selected set of results over granites are presented here as a case study highlighting the salient features of MASW. 相似文献
2.
G. S. Srinivas K. Goverdhan Ch. Narsimhulu T. Seshunarayana 《Journal of the Geological Society of India》2014,84(2):174-180
Multichannel analysis of surface waves (MASW) is a non-destructive seismic prospecting method utilizing Rayleigh waves for imaging and characterizing shallow sub-surface structure. Multichannel analysis of surface waves (MASW) studies were conducted in drift areas of two bridge sites in the hilly terrain of J&K for imaging and characterizing shallow sub-surface structure. The purpose of the present study is to estimate the shear wave velocity (VS) and subsurface structure in four drifts made in a hilly terrain for construction of two bridges. Rayleigh waves are having dispersive properties, travelling along or near the ground surface and are usually characterized by relatively low velocity, low frequency, and high amplitude. The study area comprises of Tertiary group of rocks which are underlain by Siwalik group. The main rock type in the study area is dolomite which has undergone various geological processes like weathering, jointing, fracturing and shearing. MASW data was collected inside four drifts in the mountainous terrain of J&K state which are located on either sides of Chenab river. The data was analyzed by relevant processing software using dispersion and inversion technique. Shear wave velocities were estimated up to 30 m depth. Average shear wave velocity (VS 30) up to top 30m was also computed. It is observed that, VS in the range 400–800 m/s upto 10–15 m corresponding to weathered rock, followed by compact dolomite rock up to the depth of about 30 m with VS in the range 1200–1600 m/s. Some low velocity zones are also identified from these sections which represent shear zones. 相似文献
3.
Multichannel analysis of surface waves (MASW) survey was conducted to measure shear wave velocities in order to ascertain the likely causes of road failure along LASU-IBA expressway in Alimosho local government area, Lagos, Nigeria. MASW data were acquired along the express road. The acquired dataset was processed and transformed into two-dimensional structure reflective of depth and surface wave velocity distribution within a depth of investigation using SurfSeis software. The MASW shear wave velocity data were compared to geophysical data that was acquired along the same profile. The comparison was also done with geotechnical data that had been acquired prior to the study some meters away from the study area. The correlation between N values to measured shear wave velocity using MASW was generated. The comparison illustrates the accuracy and consistency of MASW-derived shear wave velocity profiles. We concluded that (1) the low-velocity region that varies between 100 and 250 m/s at surface down to 4 m beneath the surface is characterized by loose/peat materials and may have been responsible for the road failure within the study area; this region depicts a very loose compaction area. (2) The MASW technique is a time–cost-effective tool for obtaining reliable shear wave velocity profiles, and (3) the MASW is particularly attractive in areas that cannot be readily assessed by other geophysical and geotechnical tools. 相似文献
4.
表面波有效相速度近似分析方法 总被引：1，自引：0，他引：1
分层介质中瑞利面波有多个模态,表面瞬态响应是多个模态响应的叠加。在近场,面波模态响应传播速度随传播距离而变化;在远场,其趋于模态相速度。由分层介质表面两不同点响应互谱分析(SASW)得到的有效相速度并不对应于面波基阶模态相速度,它与波场中高阶模态能量分配比例有关。有效相速度随传播距离而变化,近场体波对有效相速度影响较大。对分层介质在简谐荷载下表面质点位移响应进行了互谱分析,得到了有效相速度理论值,通过理论值与测试值匹配分析可估算分层参数,该分析方法考虑了近场及高阶面波模态对有效相速度的影响。 相似文献
5.
Shear wave velocity (V S) estimation is of paramount importance in earthquake hazard assessment and other geotechnical/geo engineering studies. In our study, the shear wave velocity was estimated from ground roll using multichannel analysis of surface wave (MASW) technique making use of dispersive characteristics of Rayleigh type surface waves followed by imaging the shallow subsurface basaltic layers in an earthquake-prone region near Jabalpur, India. The reliability of MASW depends on the accurate determination of phase velocities for horizontally traveling fundamental mode Rayleigh waves. Inversion of data from surface waves resulted in a shear wave velocity (V S) in the range of 200–1,200 m/s covering the top soil to weathering and up to bedrock corresponding to a depth of 10–30 m. The P-wave velocity (V P) obtained from refraction seismic studies at these locations found to be comparable with V S at an assumed specific Poisson’s ratio. A pair of selected set of V S profiles over basalt which did not result in a hazardous situation in an earthquake of moderate magnitude are presented here as a case study; in other words, the shear wave velocity range of more than 200 m/s indicate that the area is highly unlikely prone to liquefaction during a moderate or strong earthquake. The estimated depth to basalt is found to be 10–12 m in both the cases which is also supported by refraction studies. 相似文献
6.
Jianghai Xia Richard D Millerg Xu Yixian Luo Yinhe Chen Chao Liu Jiangping Julian Ivanov Chong Zeng 《中国地质大学学报(英文版)》2009,20(3)
High-frequency (≥2 Hz) Rayleigh-wave data acquired with a multichannei recording sys-tem have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave tech-niques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a nou-iuvasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution. 相似文献
7.
针对地基模型中可能出现泄漏模式的几种情况，对瑞利波勘探中泄漏模式波的求取进行了模拟研究。通过添加附加层的方法，使实频散方程求解瑞利波相速度的范围包含了所有的层速度区域，从而用导波来模拟计算泄漏模式波。通过对七个模型的模拟结果来看，附加层法不仅能模拟出原模型的实数导波，而且还能反映其泄露模式波的变化。同时，通过对Ⅴr-λ曲线的正演计算，说明泄漏模式波的存在也是产生“之”字形的原因之一。 相似文献
8.
地震剖面分类与浅层三种波的层位对比 总被引：1，自引：1，他引：0
3种波指的是反射纵波,折射纵波,瑞雷面波.层位对比指的是3种波波场特征对比和它们各自反演所得的波速对比.对比的目的是为了确定剖面中形成3种波的地层及其层位,为3种波交叉渗透的联合反演奠定基础.本文所述内容是同时应用3种波,进行多波勘探方法理论的重要组成部分.为适应这种新型多波勘探的正、反演,文中首先以剖面中层数和相邻层之间波速大小关系为依据,介绍剖面分类与命名的方法,而后针对本文主题,论述利用3种波的波场特征和波速关系,进行层位对比的方法. 相似文献
9.
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. 相似文献
10.
利用高频面波反演横波速度一直是浅地表地震工程研究的热点。为深入认识利用高频面波（瑞雷波和勒夫波）评价横波速度的能力,本文首先采取高阶交错网格有限差分法实现两层模型的瑞雷波和勒夫波数值模拟,并应用τ-p变换形成频散能量图。相比瑞雷波,不同模式的勒夫波频散能量很接近,这说明易于实现多模式勒夫波反演。然后利用线性映射实现广义模式识别这种非线性反演方法对含软弱夹层的四层模型的基模式、多模式瑞雷波和勒夫波的变厚度反演。若初始模型很拙劣,相比勒夫波,瑞雷波基模式反演不能重建地层中含有软弱夹层这一特征,瑞雷波多模式反演则可以重建这一特征;勒夫波基模式和多模式反演都可以重建这一特征。即使在地层的泊松比与估计值相差很大时,瑞雷波多模式反演仍能重建地层结构,但其频散曲线总是存在"模式接吻"现象,容易模式误判;而勒夫波反演则不用估计地层泊松比,也不存在"模式接吻"现象。一系列算例表明：高模式瑞雷波的加入会显著提高横波速度评价结果的精度;而高模式勒夫波的加入会令反演系统对半空间以上异常层的参数过于敏感,造成参数过度估计,但也会显著提升对半空间横波速度的评价能力。最后,应用本文方法实现了对实测勒夫波数据的分析。 相似文献
11.
This paper presents how faster two dimensional (2-D) tomography of soil layers is obtained in geotechnical characteristics through multi-channel analysis of surface wave (MASW) method. MASW is developed as a new technique incorporating multiple receivers and 2-D wave-field transformations to obtain better performance in surface wave analysis. Incorporating 2-D tomography technique with multi-channel analysis offers an efficient and cost effective technique in soil site investigations. In the previous research, the Geo-SW@T software was designed and developed with collecting a lot of records including programming array technique to show the 2-D tomography in near surface soil profiling. To make a 2-D tomography of soil profile based on the past planned MASW technique is time consuming for collecting large database through 2-D array of programming language. In this paper, a new idea is established to obtain faster performance in soil tomography profile using array and sub-array technique in MASW. The performance of newly developed tomography technique with MASW method is estimated as faster and important tomography system for using one single record in soil characterizations rather than arranging of multiple records. 相似文献
12.
This paper presents the technique to demonstrate reliable two-dimensional (2-D) tomography of near-surface soil through multichannel
analysis of surface wave (MASW) method. The MASW method is used as seismic method for determining the shear wave velocity
profile of near-surface soil with better performance. Normally, this method represents one-dimensional (1-D) soil layer profile
to delineate anomalous subsurface materials and detect soil characteristics in geotechnical investigations. Conventionally,
the MASW method is able to represent depth corresponding shear wave velocity through 1-D representation. In this paper, this
method is improved through representation of depth and distance versus shear wave velocity profile using 2-D tomography analysis
in geotechnical investigations. The outcomes of the newly developed method are more reliable and informative in comparison
to the outcome of the conventional MASW method. The significance of this research is incorporating advanced tomography technique
with MASW method to obtain 2-D tomography of geotechnical characteristics with consistency. 相似文献
13.
对于某些非规则水平层状地质剖面,采用传递矩阵法获得的瑞利波频散曲线可能会出现截止或截断现象,但采用附加层的方法可避免这些现象的发生。通过采用附加层法前后相速度与激发强度大小的对比,来论证附加层法的正确性。对3个典型的非规则剖面进行模拟计算,利用传递矩阵法算得添加附加层前后瑞利波频散曲线,以及某些特征点处位移分量随深度的变化情况。通过对计算结果的对比分析可知,附加层法不仅可计算出地质剖面的实数导波,还可算出其泄漏模式波;在固定的频率点上,附加层的埋深越大,则添加附加层后算得的激发强度大小与原模型的误差越小;当附加层的埋深固定时,添加附加层后计算出的位移曲线与原位移曲线之间的误差随着对比点频率的增大而减小。可见,今后根据实际工作的精度要求,可用附加层法计算某些非规则剖面的瑞利波频散曲线。 相似文献
14.
为了较好地模拟给定模型在随机源激发下产生的稳定波场信息,为微动信号的检验和数据特征分析等提供理论依据,采用交错网格有限差分方法模拟微动信号,并根据瑞雷波和勒夫波的产生机理,通过测区内震源的分布情况估测微动信号中面波的组成成分。首先建立交错网格有限差分法模拟微动信号的数值模型,然后给出估测微动信号中面波组成成分的算式,最后采用典型方法数值模拟微动信号,应用空间自相关方法提取模拟信号中面波的频散曲线进行分析对比。结果表明,交错网格有限差分方法模拟得到的微动信号更符合实测结果。 相似文献
15.
Propagation of Rayleigh waves in fluid‐saturated non‐homogeneous soils with the graded solid skeleton distribution 
下载免费PDF全文
下载免费PDF全文 The propagation characteristic of Rayleigh waves in a fluid‐saturated non‐homogeneous poroelastic half‐plane is addressed. Based on Biot's theory for fluid‐saturated media, which takes the inertia, fluid viscosity, mechanical coupling, compressibility of solid grains, and fluid into account, the dispersion equations of Rayleigh waves in fluid‐saturated non‐homogeneous soils/rocks are established. By considering the shear modulus of solid skeleton variation with depth exponentially, a small parameter, which reflects the relative change of shear modulus, is introduced. The asymptotic solution of the dispersion equation expressing the relationship between the phase velocity and wave number is obtained by using the perturbation method. In order to analyze the effects of non‐homogeneity on the propagation characteristic of Rayleigh waves, the variation of the phase velocity with the wave number is presented graphically and discussed through numerical examples. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
16.
17.
18.
半空间非水平层状介质瑞雷面波的频散方程 总被引：2，自引：0，他引：2
由于工程勘察中的一些特殊情况,使面波以往的一些理论和结论受到了不同程度的限制。本文从弹性动力学虚功变分原理出发,在重点分析自由表面外力提供的能量来源时,引入了等效面波(能量)震源概念。然后用有限元法建立了半空间多个非水平层状介质瑞雷西波的频散方程。这项工作有助于面波理论和应用技术的发展完善。 相似文献
19.
面波是陆上地震资料的主要干扰噪声,目前主要采用基于十字交叉排列的FKK（频率-波数-波数）面波压制技术;但其效果不理想,会损害部分有效信号的低频能量。针对此问题,提出一种面波模拟和曲波变换联合压制面波的技术。首先利用面波模拟逐级压制基阶、一阶和二阶面波;然后,再采用曲波变换方法压制残余面波。实际地震资料的处理结果表明：与三维FKK滤波相比,本文所述方法在压制面波的同时,能够保持反射波的低频信息,提高了信噪比。该技术是一种相对保幅的压制面波方法。 相似文献
20.
τ-p变换去除金属矿地震资料中的线性干扰 总被引：5，自引：1，他引：5
金属矿地震勘探资料中通常含有多种不同类型的噪声,有效地消除这些噪声,提高地震信号的信噪比是地震数据处理的主要内容之一。二维滤波(F K滤波)是消除低速干扰的一种有效手段,它可以消除视速度较低的面波及其它干扰波,但它只适用于地层倾角较缓的地区。对于复杂条件下的金属矿效果不佳。经过多次实验,用τ-p法压制线性干扰,效果显著。 相似文献