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The local geology and shallow S-wave velocity structure of a site are recognized to be key factors for the increase in the damaging potential of seismic waves. Indeed, seismic amplitudes may be amplified in frequency ranges unfavorable for building stock by the presence of soft sedimentary covers over lying hard bedrock. Hence, microzonation activities, which aim at assessing the site response as accurately as possible, have become a fundamental task for the seismic risk reduction of urbanized areas. Methods based on the measurement of seismic noise, which typically are fast, non-invasive, and low cost, have become a very attractive option in microzonation studies.Using observations derived from seismic noise recordings collected by two-dimensional arrays of seismic stations, we present a novel joint inversion scheme for surface wave curves. In particular, the Love wave, the Rayleigh wave dispersion and the HVSR curves are innovatively combined in a joint inversion procedure carried out following a global search approach (i.e., the Genetic Algorithm).The procedure is tested using a data set of seismic noise recordings collected at the Bevagna (Italy) test-site. The results of the novel inversion scheme are compared with the inversion scheme proposed by Parolai et al. (2005), where only Rayleigh wave dispersion and HVSR curves are used, and with a cross-hole survey. 相似文献
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Site characterization for design of deep foundations is very crucial, as unanticipated site conditions still represent significant problems and disputes occur during construction. Traditional surface-based geophysical methods, which use wave velocity dispersion or first-arrival times, have been widely used recently to assess spatial variation; however they cannot well characterize reverse profiles or buried low-velocity zones. For better characterization of these challenging site conditions, a full waveform inversion based on Gauss–Newton method is presented. The inversion scheme is based on a finite-difference solution of the 2-D elastic wave equation in the time domain. The strength of this approach is the ability to generate all possible wave types of seismic wavefields that are then compared with observed data to infer complex subsurface properties. Virtual sources and reciprocity of wavefields are used for calculation of partial derivative wavefields to reduce computer time. Cross convolution between observed and estimated wavefields are also employed to allow the technique to be independent of the source signatures. The capability of the presented technique is tested with both synthetic and real experimental data sets. The inversion results from synthetic data show the ability of characterizing anomalies of low- and high-velocity zones, and the inversion results from real data are generally consistent with SPT N-value, including the identification of a buried low-velocity layer. 相似文献
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Site engineering seismic survey provides basic data for seismic effect analysis. As an important parameter of soil, shear-wave velocity is usually obtained through wave velocity testing in borehole. In this paper, the passive source surface-wave method is introduced into the site engineering seismic survey and practically applied in an engineering site of Shijingshan District. By recording the ubiquitous weak vibration on the earth surface, extract the dispersion curve from the surface-wave components using the SPAC method and obtain the shear-wave velocity structure from inversion. Over the depth of 42 m underground, it totally consists of five layers with interface depth of 3.31, 4.50, 7.23, 17.41, and 42.00 m; and shear-wave velocity of 144.0, 198.3, 339.4, 744.2, and 903.7 m/s, respectively. The inversion result is used to evaluate site classification, determine the maximum shear modulus of soil, provide basis for further seismic hazard analysis and site assessment or site zoning, etc. The result shows that the passive source surface-wave method is feasible in the site engineering seismic survey and can replace boreholes, shorten survey period, and reduce engineering cost to some extent. 相似文献
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The spectral analysis of surface waves (SASW) method is an in situ, seismic method for determining the shear wave velocity (or maximum shear modulus) profile of a site. The SASW test consists of three steps: field testing, evaluation of dispersion curve by phase unwrapping method, and determination of shear modulus profile by inversion process. In general, field testing and dispersion curve evaluation are regarded as simple work. However, because of characteristic of Fourier transform used in the conventional phase unwrapping method, dispersion curve is sensitive to background noise and body waves in the low frequency range. Furthermore, under some field conditions such as pavement site, the usual phase unwrapping method can lead to erroneous dispersion curve. To overcome problem of the usual phase unwrapping method, in this paper, a new method of determining dispersion curve for SASW method was applied using time–frequency analysis based on harmonic wavelet transform as an alternative method of a current phase unwrapping method. To estimate the applicability of proposed method to SASW method, numerical simulations at various layered soil and pavement profiles were performed and the dispersion curves by proposed method are more reliable than those by the usual phase unwrapping method. 相似文献
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The discussion deals with the effect of shear wave velocity uncertainties on 1D seismic ground response analysis. In particular, the paper refers to uncertainties deriving from the solution of the inverse problem in surface wave methods. We address some issues related to the evaluation of “equivalent” profiles from surface wave data, the inversion strategy and the numerical simulation of seismic site response. The pitfalls in the analyses point out the need for more refined studies to draw general conclusions on the subject. 相似文献
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本文模拟使用青藏高原东南缘区域台网及国家台网的170个宽频台站基于背景噪声、天然地震面波、P波接收函数反演时的实际数据,对青藏高原东南缘假定的初始模型进行恢复,通过计算初始模型台站下方纯路径频散、提取各台站对间的瑞雷波频散曲线、计算理论接收函数以及反演剪切波速度结构来测试使用不同单项数据与联合使用多种数据反演对初始模型的恢复程度。结果表明,同时使用接收函数、基于噪声经验格林函数的群速度、相速度频散以及基于天然地震面波的相速度频散联合反演的剪切波速度结构,充分利用了几种数据的分辨率优势,清晰地分辨出中下地壳及上地幔顶部的低速层。此外,本文也分析了实际数据处理中出现的计算误差、随机噪声干扰对计算结果稳定性的影响。结果显示:对于面波频散,加入1%的误差后,联合反演的结果仍可很好地反映低速层的形态,但是当误差提升至5%后,对最终结果则产生了一定程度的影响;而在接收函数中加入4%的随机噪声时,虽然地幔低速层的上界面和下界面会略微受到随机噪声的影响,但是低速层的深度范围和速度值均得到了较好的恢复。 相似文献
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为了快速而且廉价地获取北京市详细的场地响应和浅层速度结构,应用于地震动模拟和地震灾害预防,我们开展了微动观测技术和处理方法研究.本文利用2007年夏季北京五棵松地区进行的几个微动观测实验数据,使用单台H/V谱比法分析场地的卓越频率及其对应的放大系数,并对比了不同地震仪和观测时间对H/V曲线的影响;应用高分辨率F-K频谱分析方法从微动台阵数据中得到Rayleigh波的频散曲线并使用邻域算法反演出浅层速度结构.H/V结果表明该地区卓越频率在2.1～2.2 Hz之间,对应的放大系数下限约为3;利用微动H/V方法得到的场地卓越频率具有较高的稳定性.微动台阵反演结果给出了比较合理的波阻抗界面深度和层平均速度结构,认为地下80多米处的波阻抗界面是决定场地卓越频率和其场地放大系数的主要界面.本研究表明微动技术应用于评估城市地震场地响应和浅层速度结构是可行且易于实施的. 相似文献
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Fabrice Hollender Cécile Cornou Aline Dechamp Kaveh Oghalaei Florence Renalier Emeline Maufroy Clément Burnouf Sylvette Thomassin Marc Wathelet Pierre-Yves Bard Vincent Boutin Clément Desbordes Isabelle Douste-Bacqué Laetitia Foundotos Cédric Guyonnet-Benaize Vincent Perron Julie Régnier Agathe Roullé Mickael Langlais Deborah Sicilia 《Bulletin of Earthquake Engineering》2018,16(6):2337-2365
Data provided by accelerometric networks are important for seismic hazard assessment. The correct use of accelerometric signals is conditioned by the station site metadata quality (i.e., soil class, VS30, velocity profiles, and other relevant information that can help to quantify site effects). In France, the permanent accelerometric network consists of about 150 stations. Thirty-three of these stations in the southern half of France have been characterized, using surface-wave-based methods that allow derivation of velocity profiles from dispersion curves of surface waves. The computation of dispersion curves and their subsequent inversion in terms of shear-wave velocity profiles has allowed estimation of VS30 values and designation of soil classes, which include the corresponding uncertainties. From a methodological point of view, this survey leads to the following recommendations: (1) perform both active (multi-analysis surface waves) and passive (ambient vibration arrays) measurements to derive dispersion curves in a broadband frequency range; (2) perform active acquisitions for both vertical (Rayleigh wave) and horizontal (Love wave) polarities. Even when the logistic contexts are sometimes difficult, the use of surface-wave-based methods is suitable for station-site characterization, even on rock sites. In comparison with previous studies that have mainly estimated VS30 indirectly, the new values here are globally lower, but the EC8-A class sites remain numerous. However, even on rock sites, high frequency amplifications may affect accelerometric records, due to the shallow relatively softer layers. 相似文献
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对2001年昆仑山口西Ms81级地震产生的断层带,布设了沿断层和横跨断层的两条人工地震测线.通过对观测资料的定量分析和处理,求得了昆仑山断层带内部的细结构.分析工作包括从S波震相开始的振幅谱计算、速度频散计算、群速度测量,并用面波频散方法反演S波速度结构,用振幅谱比的方法估计断层带的Q值.野外试验结果表明,S波震相与围陷波组的时间差随炮点与台站之间距离增大而增加,在断层带外的测点上观测到与断层带相关的场地效应.最后得出昆仑山断层带宽度为250m、速度结构为断层内低速的分层结构和Q值为15（断层内）和30（围岩）.虽然昆仑山口西地震的震级比美国加州Landers地震的震级（Ms76）大,且地震产生的破裂带长度长得多,但是这两个地震断层带的宽度却相差不大. 相似文献
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Ambient seismic noise or microtremor observations used in spatial auto-correlation (SPAC) array methods consist of a wide frequency range of surface waves from the frequency of about 0.1 Hz to several tens of Hz. The wavelengths (and hence depth sensitivity of such surface waves) allow determination of the site S-wave velocity model from a depth of 1 or 2 m down to a maximum of several kilometres; it is a passive seismic method using only ambient noise as the energy source. Application usually uses a 2D seismic array with a small number of seismometers (generally between 2 and 15) to estimate the phase velocity dispersion curve and hence the S-wave velocity depth profile for the site. A large number of methods have been proposed and used to estimate the dispersion curve; SPAC is the one of the oldest and the most commonly used methods due to its versatility and minimal instrumentation requirements. We show that direct fitting of observed and model SPAC spectra generally gives a superior bandwidth of useable data than does the more common approach of inversion after the intermediate step of constructing an observed dispersion curve. Current case histories demonstrate the method with a range of array types including two-station arrays, L-shaped multi-station arrays, triangular and circular arrays. Array sizes from a few metres to several-km in diameter have been successfully deployed in sites ranging from downtown urban settings to rural and remote desert sites. A fundamental requirement of the method is the ability to average wave propagation over a range of azimuths; this can be achieved with either or both of the wave sources being widely distributed in azimuth, and the use of a 2D array sampling the wave field over a range of azimuths. Several variants of the method extend its applicability to under-sampled data from sparse arrays, the complexity of multiple-mode propagation of energy, and the problem of precise estimation where array geometry departs from an ideal regular array. We find that sparse nested triangular arrays are generally sufficient, and the use of high-density circular arrays is unlikely to be cost-effective in routine applications. We recommend that passive seismic arrays should be the method of first choice when characterizing average S-wave velocity to a depth of 30 m (Vs30) and deeper, with active seismic methods such as multichannel analysis of surface waves (MASW) being a complementary method for use if and when conditions so require. The use of computer inversion methodology allows estimation of not only the S-wave velocity profile but also parameter uncertainties in terms of layer thickness and velocity. The coupling of SPAC methods with horizontal/vertical particle motion spectral ratio analysis generally allows use of lower frequency data, with consequent resolution of deeper layers than is possible with SPAC alone. Considering its non-invasive methodology, logistical flexibility, simplicity, applicability, and stability, the SPAC method and its various modified extensions will play an increasingly important role in site effect evaluation. The paper summarizes the fundamental theory of the SPAC method, reviews recent developments, and offers recommendations for future blind studies. 相似文献
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《Journal of Applied Geophysics》2006,58(2):87-98
A geophysical campaign to characterize the subsurface of a contaminated site down to a depth of several tens of meters was carried out under the HYGEIA-CEE project. On this site, seismic techniques were combined to image the geological structures; i.e. seismic reflection, P-wave tomography and spectral analysis of surface waves. Because these techniques consider different wave components in the processing, they can be expected to provide complementary information concerning the site lithology. The special feature of this experiment is the fact that the same seismic acquisition device, consisting of a mobile central unit, a drop-weight seismic source, and a sensor line of gimbal mounted geophones, was used for each of the techniques. Two perpendicular seismic lines were set up in the field for testing two geophone spacings. Three processing procedures, one each for the seismic reflection, P-wave tomography and spectral analysis of surface waves, were developed for producing seismic images from the P-wave reflectivity, the first P-wave arrivals and the dispersion of Rayleigh waves, respectively. The images show good complementarity in terms of investigation depth. The results are also in good agreement with available borehole data: the sandy layers seem to be related to low velocities, since the high velocities are better explained by the presence of clayey and gravelly intervals. The contribution and the limits of this seismic multi-approach method is discussed. 相似文献
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《Journal of Applied Geophysics》2007,61(1):56-81
Due to the character of seismic energy generation and propagation, shallow high-resolution seismic-reflection surveys often fail in the identification of the shallowest horizons and, due to the limited offsets, accuracy of velocity analyses is often not very high.In recent years, Rayleigh wave dispersion analysis have proved to have good potential also for near-surface applications but dispersion curve inversion and related uncertainty evaluation pose serious problems to a completely stand-alone application.In order to overcome these problems a joint inversion scheme is proposed, which is based on the identification of the Pareto front, performed in the framework of a Multi-Objective Evolutionary Algorithm (MOEA). Seismic data considered to design the two objectives are the Rayleigh wave dispersion curve and reflection travel times.We initially analyse a set of synthetic cases and evaluate the obtained results. A significant improvement of the retrieved models is observed as long as reflection travel times are added to the dispersion curve alone.Furthermore, the proposed methodology also provides relevant indications about the consistency of the overall inversion process. In fact, the distribution of the models in the objective space, the trend of the objectives over the passing generations and the evolution of the Pareto front can provide useful information to evaluate the provisional tentative interpretation (number of strata and reflector identification) inherently adopted for the data inversion.On the basis of the results obtained from the tests on the synthetic datasets, the analyses of a field dataset are interpreted as possible evidence of lateral heterogeneities. 相似文献
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Dimitrios G. Raptakis 《Soil Dynamics and Earthquake Engineering》2012,34(1):69-77
There are many publications on the investigation of soil properties using seismic prospecting. Among these properties, special attention has been given to shear wave velocity VS, using more than two different methods for soil and site characterization. In this study, the in-hole, non-invasive refraction and surface wave inversion methods to evaluate soil improvement are investigated. The investigation was conducted on the new Egnatia highway (Northern Greece). Wave velocity profiles have been measured before and after preloading for the construction of an embankment at a soft soil site. The purpose is to quantify the dynamic properties and to evaluate the efficiency of the applied tools in detecting their variation. Among others, an emphasis was given to the observed improvement at particular layers of high sand content. 相似文献
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Antoni M. Correig 《Pure and Applied Geophysics》1991,136(4):561-576
Generalizing previous studies on short-period data, it is shown that body-wave dispersion can be measured from broad-band records of earthquakes of moderate magnitude. The method is based on the direct measurement of the arrival time of the frequency components of a seismic wave, and the arrival time is defined by its expectation value. The frequency components of the signal are obtained through a narrow band-pass filtering process. Previous to any interpretation, a correction of the arrival time for instrument response and group delay of the filter is needed. In the first step, body-wave dispersion is related to an absorption band to account for intrinsic attenuation, and thereafter we generalize this interpretation by considering a cascade of filters to account for medium parameters (attenuation and a layered crust) and source parameters (source time function and finiteness of fault). An inversion scheme to obtain the filter parameters can be devised by following, in a formal way, the same procedure as for the case of surface wave dispersion. 相似文献
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In this paper,the dispersion curves of the Rayleigh wave and Love wave were extracted from the seismic noise records of 25 broadband stations of the Fujian Seismic Network, and inverted for the lithosphere velocity structure. Furthermore,the velocity model was verified by the seismic explosion observations. Our results indicate that the resolution of the lithosphere velocity structure obtained by this method is good in the shallow part,but in the deep part,inversion accuracy for the wave velocity structure is low,which is caused mainly by the small inter-station distance chosen in the paper. Thus the wave dispersion curves have high accuracy in the short-period part,but the warp of the wave dispersion curve in long-period part is large. Considering the results from both the noise inversion and the traditional inversion,we finally present a new velocity model,and the theoretical travel time calculated with the new model matches the explosion travel time very well. 相似文献