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1.
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. VS,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. 相似文献
2.
In a companion paper local transfer functions were estimated at Tecoman using earthquake and microtremor data. In this paper, the subsoil structure at this city is investigated using seismic refraction and cross-correlation of noise records as a case study. P- and S-wave refraction profiles were measured at five sites within the city. Standard analysis constrained only very shallow layers. The P-wave refraction deployment was also used to record ambient vibration. These data were processed using an extension of the SPAC (SPatial AutoCorrelation (Aki, 1957) [1]) method; cross-correlation is computed between station pairs and the results are inverted to obtain a phase velocity dispersion curve. Penetration depth was larger than that from the refraction experiments but the shear-wave velocity of the basement could not be determined. For this reason, additional microtremor measurements were made using broad band seismometers with a larger spacing between stations. The results allowed to constrain the shear-wave velocity of the basement. Site amplification computed for the final profiles compare well with observed ground motion amplification at Tecoman. The case of Tecoman illustrates that even a simple subsoil structure may require crossing data from different experiments to correctly constrain site effects. 相似文献
3.
Array measurements of microtremors were carried out at thirty sites in Damascus city, Syria to estimate S-wave velocity structures of shallow soil formations for site effect analysis. The microtremor data were recorded by 6 vertical-component seismometers distributed along the circumferences of two circles as well as a 3-component seismometer deployed in the center. The phase velocities were estimated at each site from the vertical components of recorded microtremor data by using the Spatial Autocorrelation method. Then, Genetic Simulated Annealing Algorithm technique was applied for inversion of the phase velocities to estimate 1-D S-wave velocity structures beneath the sites. The inverted Vs profiles are not uniform in Damascus city and the results show that a shallow soft layer (∼200 m/s) appears in the eastern part of the city as well as the central part along Barada River. This layer controls the amplification distribution in the city with a high amplification mainly observed at the locations having this layer. The inversion results also show that the depth to the engineering bedrock (∼750 m/s) is very shallow along the foothills of Mt. Qasyoun in the north-west. Then the depth increases towards the east and the south. The maximum depth to the engineering bedrock (∼80 m) was observed in the southern part of Damascus. To validate the results of the inversions, the spectral ratios between the horizontal and vertical components (H/V) of the recorded microtremor data at the central seismometer were compared with the computed ellipticities of the fundamental-mode Rayleigh-waves based on the respective Vs structure. The results show a good agreement in a period range of 0.05 s to 0.5 s. In this period range, the dominant peaks of the H/V ratios are due to the overall effect of the velocity contrasts between the shallow layers representing the subsurface S-wave velocity structure. Moreover, the average S-wave velocity for the top 10 m of soils (VS10) shows a better correlation with the averaged site amplification in a period range of 0.05 s to 0.5 s than VS30 which indicates that VS10 can be a better proxy for high-frequency site amplification in the case of Damascus city. 相似文献
4.
Juan C. Tokeshi Madan B. Karkee Yoshihiro Sugimura 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):163-174
The paper utilizes previously developed microtremor simulation technique to evaluate the reliability of Rayleigh wave dispersion curve estimated by f–k spectral analysis of microtremor array measurement. The simulated microtremors are obtained for a fictitious (TEST) site. Attempt is also made to obtain the dispersion curve for two real sites (OHDATE and SKC) by inverse analysis of the microtremor array measurement using f–k spectra method. The estimated dispersion curve from simulated microtremors (TEST site) compares well with the theoretical dispersion curve, demonstrating the reliability of f–k spectra method and indicating that the estimated dispersion curve from microtremor measurements could be adequately used as the target for inverse analysis purposes. It is also demonstrated that the dispersion curve from microtremor measurements can be utilized to estimate the soil profile at OHDATE and SKC sites by inverse analysis. Results show that the theoretical dispersion curve of the fundamental mode of Rayleigh wave after the end of inverse analysis are in good agreement with the dispersion curve obtained by f–k spectral analysis of microtremor array measurement. 相似文献
5.
为了避免微动勘探技术中因忽略高阶模式瑞雷波而影响反演精度的不足,提出从微动面波中提取多模式瑞雷波频散曲线的映射式方法.该方法从微动信号入手,首先通过相关法提取多半径台阵的相关系数曲线,然后建立从多条相关系数曲线到多模式瑞雷波频散曲线的映射模型,最后采用分区拟合准则优化实现模型结构,达到提取微动面波中多模式瑞雷波频散曲线的目的.为验证方法的有效性,通过有限差分方法数值计算实际近表面应用中三种常见典型地质结构中的微动信号,采用映射式方法提取微动面波中多模式瑞雷波频散曲线,将提取结果和理论值进行对比分析.结果表明,映射式方法提取微动面波中多模式瑞雷波频散曲线可以满足反演地质结构的要求. 相似文献
6.
The 1999 Chi-Chi, Taiwan earthquake, MW = 7.6, caused severe damage in the near-fault region of the earthquake. In order to evaluate site effects in the near-field strong motions we estimate S-wave velocity structures of sediments at four sites using array records of microtremors. We also recalculated S-wave velocity structures at other four sites previously reported. To show the validity of the estimated S-wave velocity structures we separate empirical site responses from aftershock records using the generalized inversion method and show the agreement between empirical and theoretical site responses. We also show an observed fact that suggests soil nonlinearity during the Chi-Chi earthquake by comparing horizontal-to-vertical spectral ratios (HVRs) for main shock records with HVRs for aftershock records. Then we calculate one-dimensional equivalent-linear site responses using the estimated S-wave velocity structures and the main shock records observed on the surface. It is found that site amplification due to thick (about 6 km) sediments is one of the important factors for explaining the long-period velocity pulses of about 5 to 10 sec observed at sites in the footwall during the Chi-Chi earthquake. It is also found that the theoretical site responses of shallow soft sediments at sites that sustained severe damage in the hanging wall shows significant amplification around 1 sec. As the amplitude of velocity pulses with period around 1 sec is most critical in causing damage to ordinary buildings of moderate heights, our results suggest that the 1-sec period velocity pulses, amplified by the site response of shallow sediments should contribute to the severe damage during the Chi-Chi earthquake. 相似文献
7.
Measurement of shallow shear wave velocities at a rock site using the ReMi technique 总被引：1，自引：0，他引：1
A. Pancha J.G. Anderson J.N. Louie S.K. Pullammanappallil 《Soil Dynamics and Earthquake Engineering》2008,28(7):522-535
Shallow shear wave velocities beneath a rock site are characterized using the refraction microtremor (ReMi) technique developed by Louie [Faster, better: shear-wave velocity to 100 m depth from ReMi arrays. Bull Seism Soc Am 2001; 91: 347–64]. Ground motion from a passing train enabled capture of energy propagating parallel to the recording array. This allowed evaluation of the variation of the minimum phase-velocity of the dispersion curve envelope and better estimation of the true minimum velocity beneath the site. We use a new method to image and evaluate the dispersion curve envelope via power–slowness profiles through the slowness–frequency plots introduced by Louie [Faster, better: shear-wave velocity to 100 m depth from ReMi arrays. Bull Seism Soc Am 2001; 91: 347–64]. Data illustrated the frequency dependency of dispersion curve uncertainties, with greater uncertainty occurring at low frequencies. These uncertainties map directly into uncertainty of the inverted velocity–depth profile. Above 100 m depth velocities are well constrained with 10% variability. Variability is greatly reduced when the energy propagation is along the geophone array. Greater velocity variation is observed below 100 m depth. 相似文献
8.
Earthquake has left much life and property damages. The occurrence of such events necessitates the execution of plans for combating the earthquakes. One of the most important methods for combating earthquakes includes assessing dynamic characteristics of soil and site effect. One of the methods by which one can state dynamic characteristics of the soil of an area is the measurement of microtremors. Microtremors are small-scale vibrations that occur in the ground and have an amplitude range of about0.1–1 microns. Microtremor measurement is fast, applicable, cost-effective. Microtremor measurements were taken at 15 stations in the Babol, north of Iran. Regarding H/V spectral ratio method, peak frequency and amplification factor were calculated for all microtremor stations.According to the analysis, the peak frequency varies from0.67 to 8.10 Hz within the study area. Also, the authors investigated the validity of the results by comparing them with SESAME guidelines and geotechnical conditions of study area. The microtremor analysis results are consistent with SESAME guidelines and geotechnical condition of study area. The results show that the microtremor observations are acceptable methods for assessing dynamic characteristics of soil and site effect in the Babol City. 相似文献
9.
10.
Marc Wathelet Denis Jongmans Matthias Ohrnberger Sylvette Bonnefoy-Claudet 《Journal of Seismology》2008,12(1):1-19
Valuable information about one-dimensional soil structures can be obtained by recording ambient vibrations at the surface,
in which the energy contribution of surface waves predominates over the one of other types of waves. The dispersion characteristics
of surface waves allow the retrieval of the shear-wave velocity as a function of depth. Microtremor studies are usually divided
in two stages: deriving the dispersion (or auto-correlation) curve from the recorded signals and inverting it to obtain the
site velocity profile. The possibility to determine the dispersion curve over the adequate frequency range at one site depends
on the array aperture and on the wavefield spectra amplitude that can be altered by filtering effects due to the ground structure.
Microtremors are usually recorded with several arrays of various apertures to get the spectral curves over a wide frequency
band, and different methods also exist for processing the raw signals. With the objective of defining a strategy to achieve
reliable results for microtremor on a shallow structure, we analyse synthetic ambient vibrations (vertical component) simulated
with 333 broadband sources for a 25-m deep soil layer overlying a bedrock. The first part of our study is focused on the determination
of the reliable frequency range of the spectral curves (dispersion or auto-correlation) for a given array geometry. We find
that the wavenumber limits deduced from the theoretical array re sponse are good estimates of the valid spectral curve range.
In the second part, the spectral curves are calculated with the three most popular noise-processing techniques (frequency–wavenumber,
high-resolution frequency–wavenumber and spa tial auto-correlation methods) and inverted indi vidually in each case. The inversions are
performed with a tool based on the neighbour hood algorithm that offers a better estimation of the global uncertainties than
classical linearised methods, especially if the solution is not unique. Several array apertures are necessary to construct
the dispersion (auto-correlation) curves in the appropriate frequency range. Considering the final velocity profiles, the
three tested methods are almost equivalent, and no significant advantage was found for one particular method. With the chosen
model, all methods exhibit a penetration limited to the bedrock depth, as a consequence of the filtering effect of the ground
structure on the vertical component, which was observed in numerous shallow sites. 相似文献
11.
工程场地动力特性分析的地脉动法 总被引：2，自引：1，他引：1
简要地回顾了地脉动研究的历史,综述了地脉动在场地动力分析中应用的四种主要分析方法：直接富氏谱法、相对参考点谱比法、单点地脉动谱比法和利用地脉动反演场地剪切波速法。介绍各种分析方法的理论依据和适用条件,侧重分析了各种方法中存在的问题,论述了地脉动的应用前景和进一步研究的内容。 相似文献
12.
Site classification of Turkish national strong-motion stations 总被引：1，自引：0，他引：1
M. Abdullah Sandıkkaya Mustafa Tolga Yılmaz B. Sadık Bakır Özdoğan Yılmaz 《Journal of Seismology》2010,14(3):543-563
Since 1973, the General Directorate of Disaster Affairs of Turkey has deployed several strong-motion accelerographs at selected
sites. Within the framework of the project entitled Compilation of National Strong Ground Motion Database in Accordance with International Standards, site conditions were investigated within the upper 30-m depth by surface seismic and standard penetration tests. Preliminary
characterization of the sites is made by making use of both geophysical and geotechnical criteria of NEHRP Provisions and
Eurocode-8 site classification systems. The liquefaction susceptibility of those sites which comprise saturated cohesionless
deposits is also determined. Mean shear-wave velocity, mean penetration resistance, site class, and liquefaction susceptibility
of each site are tabulated. The Turkish strong-motion database supplemented by detailed information on site conditions is
a valuable source of information particularly for those studies that put emphasis on the relationship between site conditions
and strong-motion parameters. 相似文献
13.
基于强震动观测台钻孔数据, 统计得到了四川、 甘肃地区20 m深的浅硬土层场地平均剪切波速模型． 通过与美国加州地区的波速模型对比, 结合四川、 甘肃地区地震预报的地壳模型, 延拓剪切波速模型至40 km． 应用四分之一波长法计算了浅硬土层场地的平均场地放大系数． 利用场地放大系数, 消除13次余震中浅硬场地的台站场地响应, 反演了龙门山断层上、 下盘的介质品质因子以及13次余震的有效应力降． 通过与普通土层场地的强震动记录对比, 对浅硬土层场地的放大系数进行调整, 得到了深厚土层场地的平均放大系数． 相似文献
14.
The authors apply soil response estimation techniques employing accelerograms for fifteen earthquakes recorded at the Yokohama Strong Motion Network and its vertical array of nine sites, plus microtremor data recorded at all 150 sites. Assessment of the reliability of surface to reference site spectral ratios, and horizontal to vertical spectral ratios of S‐waves, coda, and microtremors, relied on cross‐validation with both surface to borehole spectral ratios, and theoretical soil response functions for vertically incident SH plane waves calculated from the vertical array recordings and logging data, respectively. The results indicate the following: (1) the reference site method provides more accurate soil response estimations; (2) the H/V of microtremors provides relatively better soil response estimations than its S‐wave and coda counterparts; and (3) the H/V of microtremors provides coincident soil response estimations at two‐thirds of the sites when considering no more than ±30% mismatch in the determination of the predominant periods. The matching of parameters obtained from the analysis of microtremors, combined with their relatively low economic cost and the possibility of recording without strict spatial or time restrictions turns microtremors into a particularly appealing approach. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
15.
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
16.
Chun-Hsiang Kuo Kuo-Liang Wen Hung-Hao Hsieh Tao-Ming Chang Che-Min Lin Chun-Te Chen 《Soil Dynamics and Earthquake Engineering》2011
The shear wave velocity of shallow sediments is very important in seismic wave amplification and thus Vs30 is a well-known parameter for site classification. Based on the relationship between Vs and soil indexes, the empirical regression equations were evaluated using more than 600 data sets from the Ilan area and the Taipei Basin. Multivariable analysis, which can increase the accuracy of regression equations, was used in this study. Three extrapolations were compared, and then the most accurate bottom-constant extrapolation was adopted to estimate Vs30 at 16 boreholes, none of which reached a depth of 30 m. Ultimately Vs30 was derived for 110 free-field strong motion stations, and the stations in northeastern Taiwan were reclassified according to the Vs30-based NEHRP provisions. Regression equations of Vs and the extrapolation of Vs30 were also applied to boreholes with only N-values and corresponding depths of less than 30 m for assessing the Vs30 and NEHRP class. 相似文献
17.
Hiroaki Yamanaka Ögur Tuna Özmen Kosuke Chimoto Mehmet Akif Alkan Muammer Tün Emrah Pekkan Oguz Özel Derya Polat Murat Nurlu 《Journal of Seismology》2018,22(5):1127-1137
We have explored 1D S-wave velocity profiles of shallow and deep soil layers over a basement at strong motion stations in Eskisehir Province, Turkey. Microtremor array explorations were conducted at eight strong motion stations in the area to know shallow 1D S-wave velocity models. Rayleigh wave phase velocity at a frequency range from 3 to 30 Hz was estimated with the spatial autocorrelation analysis of array records of vertical microtremors at each station. Individual phase velocity was inverted to a shallow S-wave velocity profile. Low-velocity layers were identified at the stations in the basin. Site amplification factors from S-wave parts of earthquake records that had been estimated at the strong motion stations by Yamanaka et al. (2017) were inverted to the S-wave velocities and Q-values of the sedimentary layers. The depths to the basement with an S-wave velocity of 2.2 km/s are about 1 km in the central part of the basin, while the basement becomes shallow as 0.3 km in the marginal part of the basin. We finally discussed the effects of the shallow and deep sedimentary layers on the 1D S-wave amplification characteristics using the revealed profiles. It is found that the shallow soil layers have no significant effects in the amplification at a frequency range lower than 3 Hz in the area. 相似文献
18.
本文对龙湖地区地面脉动的测试结果,结合该地区的土层剪切波速度Vs,第四纪复盖层厚度H,进行分析研究。求得了本地区地面脉动卓越周期T的统计计算式:T=1.8H/Vs。应用这个计算式,根据实测的地面脉动卓越周期,剪切波速度的数据,推算第四纪复盖层厚度,得到了比较满意的结果。 本文的统计计算式与日本学者金井清提出的计算公式T=4H/Vs,有相同的比例关系,但有明显差别的比例常数。文中对此及一些有关问题进行了简要的定性讨论。 综合分析结果,我们认为,地面脉动的卓越周期与场地土的动力特性密切相关,而且有可能反应小区域范围场地土层的动力性质。 相似文献
19.
During the Mw = 7.4 Izmit earthquake of 17 August 1999, the Yeilyurt district of Istanbul underwent damage despite the epicentral distance of 90 km. At Avclar (20 km west of Yeilyurt), the ground motion was even stronger and has caused heavy damage and fatalities. We investigate whether the observed ground motions can be explained by theoretical site amplifications calculated from one-dimensional (1-D) shear-wave velocity models. For this purpose, microtremors recorded with sensor-arrays set up at two sites were analyzed to obtain phase velocity dispersion curves using both the conventional and the Capon frequency–wavenumber (f–k) methods. At the Yeilyurt site, the conventional f–k method offered reliable phase velocity estimations whereas the Capon method showed scatter in the estimations. At the Avclar site, on the other hand, the Capon method provided a higher resolution than the conventional method and hence, allowed estimation of wavelengths up to seven times the array size. At the Yeilyurt site, the shallow shear-wave velocity profile that is correlated with the lithology obtained from boreholes yields a ground motion amplification factor of about 3 at the frequency of 1 Hz. At the Avclar site, the phase velocity dispersion curve is comparable with the one previously obtained using the spatial autocorrelation method. The site amplification factors calculated from the 1-D shear-wave velocity model are around 2–3 at the frequencies of 0.4, 1.2 and 2.3 Hz, which are about 2–3 times smaller than the amplifications obtained from reference-site techniques using weak/strong motion records of earthquakes. We suggest that the discrepancy may be caused by a 2- or 3-D effect introduced by surface and/or bedrock topography not accounted for by the horizontally stratified model considered here. 相似文献
20.
The subsurface shear-wave velocity (Vs) is considered to be a key parameter for site characterization and assessment of earthquake
hazard because of its great influence on local ground-motion amplification. Array microtremor measurements are widely used
for the estimation of shear-wave velocities. Compared to other methods such as frequency-wavenumber (f-k) methods, the spatial
autocorrelation (SPAC) method requires fewer sensors and thus is relatively easier to implement and gives robust estimations
of shear-wave velocity profiles for depths down to a few hundred meters. The quantity derived from observed data is the SPAC
coefficient, which is a function of correlation distance, frequency and phase velocity. Generally, estimation of Vs profiles
is a two stage process: Estimation of the dispersion data from the SPAC coefficients and inversion of the dispersion data
for shear-wave velocity structure. In this study, instead of inverting dispersion curves, a more practical approach is used;
that is, observed SPAC coefficients are directly inverted for the S-wave velocities. A synthetic case and a field data application
are presented to test the potential of the inversion algorithm. We obtain an iterative damped least-squares solution with
differential smoothing. The differential smoothing approach constrains the change in shear-wave velocities of the adjacent
layers and thus stabilizes the inversion. 相似文献