共查询到20条相似文献,搜索用时 500 毫秒
1.
Abd el-aziz Khairy Abd el-aal 《Journal of Seismology》2018,22(5):1315-1323
In this contribution, new relationship between the fundamental site frequency and the thickness of soft sediments is obtained for many sites in Egypt. The Horizontal-to-Vertical Spectral Ratio (“H/V”) technique (known as Nakamura technique) can be used as a robust tool to determine the thickness of soft sediments layers overlaying bedrock from observations and measurements of seismic ambient noise data. In Egypt, numerous seismic ambient noise measurements have been conducted in several areas to determine the dynamic properties of soft soil for engineering purposes. At each site in each studied area, the fundamental site frequency was accurately estimated from the main peak in the spectral ratio between the horizontal and vertical component. Consequently, an extensive database of microtremor measurements, well logging data, and shallow seismic refraction data have been configured and assembled for the studied areas. New formula between fundamental site frequency (f0) and thickness of soft sediments (h) is established. The new formula has been validated and compared with other formulas of earlier scientists, and the results indicate that the calculated depth and geometry of the bedrock surface using new formula are in a good agreement with well logs data and previously published seismic refraction surveys in the investigated sites. 相似文献
2.
Throughout their long history, the towns of Lod and Ramle have been severely affected by strong earthquakes. The last destructive
earthquake occurred on July 11, 1927 and caused the destruction of large parts of these cities, reaching a seismic intensity
of VIII–IX on the MSK scale. Such a high intensity from a relatively distant earthquake (about 70 km) of magnitude 6.2 is
likely to be the result of local site effects of the sedimentary layers that may have significantly enhanced earthquake ground
motions.
This study is focused on estimating the seismic hazard to Lod and Ramle by implementing a three-step process (1) detailed
mapping of the characteristics of the H/V spectral ratios from ambient noise, (2) incorporating geological information and well data to construct subsurface models
for different sites within the investigated area and (3) estimating the seismic hazard in terms of uniform hazard site-specific
accelerations.
The horizontal-to-vertical spectral ratios of ambient noise were used to approximate the fundamental resonance frequencies
of the subsurface and their associated amplitudes. About 360 sites in Lod and Ramle were instrumented for varying periods.
The soil sites exhibits H/V peak amplitudes ranging from 4 to 6 in the frequency range 0.5–2.5 Hz. These data were used to constrain 1-D subsurface models
that were developed using geological data and borehole information. H/V spectral ratio observations were checked against theoretical subsurface transfer functions at locations where borehole information
is available farther constraint the range of possible Vs velocities of the different layers and thus, by means of trial an error it was possible to conclude a systematic spatial
distribution of the Vs velocity and thickness in the substrata that are also consistent with the spatial distribution of the fundamental resonance
frequencies of the soft sediments obtained by means of the H/V spectral ratios, and other geological and geophysical information available at different locations in the study area.
The evaluated subsurface models are introduced using the SEEH procedure of Shapira and van~Eck [(1993) Natural Hazards 8, 201–205] to assess Uniform Hazard Site-Specific Acceleration Spectra for different zones within the towns of Lod and Ramle.
These evaluations are very important for realistic assessment of the vulnerabilities of all types of existing and newly designed
structures and for urban and land use planning. 相似文献
3.
Philippe Guéguen Cécile Cornou Stéphane Garambois Julien Banton 《Pure and Applied Geophysics》2007,164(1):115-134
The H/V spectral ratio method based on seismic noise (HVSRN) was used in the Grenoble Basin (France), an Alpine valley characterized
by a small apex ratio. The resonance frequencies obtained in the experiments were compared to the thickness of the sediments
deduced from a microgravimetric survey and to the 1-D theoretical assessment of site responses. Given the abundance of data
on the sediments and depth of the basin, the values of the theoretical resonance frequency fo can be determined quite accurately. However, it has been observed that the effects of basin geometry can disturb fo measurements using the HVSR method, in particular for a case like the Grenoble Basin, which has a small apex ratio (w/H)
and strong suspected 2-D and/or 3-D effects. Interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10% in certain cases, with the most significant
errors (>50%) occurring on the edges of the basin, where subsurface layers are characterised by larger heterogeneities and
where the basin topography is accentuated. This study suggests that great care must be taken when using the HVSRN method as
an exploration tool, at least in valleys with a small apex ratio. 相似文献
4.
5.
R. Maresca L. Nardone G. Pasquale F. Pinto F. Bianco 《Pure and Applied Geophysics》2012,169(7):1173-1188
The effects of surface geology on ground motion provide an important tool in seismic hazard studies. It is well known that the presence of soft sediments can cause amplification of the ground motion at the surface, particularly when there is a sharp impedance contrast at shallow depth. The town of Avellino is located in an area characterised by high seismicity in Italy, about 30?km from the epicentre of the 23 November 1980, Irpinia earthquake (M?=?6.9). No earthquake recordings are available in the area. The local geology is characterised by strong heterogeneity, with impedance contrasts at depth. We present the results from seismic noise measurements carried out in the urban area of Avellino to evaluate the effects of local geology on the seismic ground motion. We computed the horizontal-to-vertical (H/V) noise spectral ratios at 16 selected sites in this urban area for which drilling data are available within the first 40?m of depth. A Rayleigh wave inversion technique using the peak frequencies of the noise H/V spectral ratios is then presented for estimating Vs models, assuming that the thicknesses of the shallow soil layers are known. The results show a good correspondence between experimental and theoretical peak frequencies, which are interpreted in terms of sediment resonance. For one site, which is characterised by a broad peak in the horizontal-to-vertical spectral-ratio curve, simple one-dimensional modelling is not representative of the resonance effects. Consistent variations in peak amplitudes are seen among the sites. A site classification based on shear-wave velocity characteristics, in terms of Vs30, cannot explain these data. The differences observed are better correlated to the impedance contrast between the sediments and basement. A more detailed investigation of the physical parameters of the subsoil structure, together with earthquake data, are desirable for future research, to confirm these data in terms of site response. 相似文献
6.
Prantik Mandal R K Chadha C Satyamurty I P Raju N Kumar 《Pure and Applied Geophysics》2005,162(12):2479-2504
Site response in the aftershock zone of 2001 Bhuj Mw 7.7 earthquake has been studied using the H/V spectral ratio method using 454 aftershocks (Mw 2.5–4.7) recorded at twelve three-component digital strong motion and eight three-component digital seismograph sites. The
mean amplification factor obtained for soft sediment sites (Quaternary/Tertiary) varies from 0.75–6.03 times for 1–3 Hz and
0.49–3.27 times for 3–10 Hz. The mean amplification factors obtained for hard sediment sites (hard Jurassic/Mesozoic sediments)
range from 0.32–3.24 times for 1–3 Hz and 0.37–2.18 times for 310 Hz. The upper bounds of the larger mean amplification factors
for 1–3 Hz are found to be of the order of 3.13–6.03 at Chopadwa, Vadawa, Kavada, Vondh, Adhoi, Jahwarnagar and Gadhada, whereas,
the upper bounds of the higher mean amplification factors at 3–10 Hz are estimated to be of the order of 2.00–3.27° at Tapar,
Chopadwa, Adhoi, Jahwarnagar, Gandhidham and Khingarpur. The site response estimated at Bhuj suggests a typical hard-rock
site behavior. Preliminary site response maps for 1–3 Hz and 310 Hz frequency ranges have been prepared for the area extending
from 23–23.85 °N and 69.65–70.85°E. These frequency ranges are considered on the basis of the fact that the natural frequencies
of multi-story buildings (3 to 10 floor) range between 1–3 Hz, while the natural frequencies for 1 to 3 story buildings vary
from 3–10 Hz. The 1–3 Hz map delineates two distinct zones of maximum site amplification (>3 times): one lying in the NW quadrant
of the study area covering Jahwarnagar, Kavada and Gadadha and the other in the SE quadrant of the study area with a peak
of 6.03 at Chopadwa covering an area of 70 km × 50 km. While the 3–10 Hz map shows more than 2 times site amplification value
over the entire study area except, NE quadrant, two patches in the southwest corner covering Bhuj and Anjar, and one patch
at the center covering Vondh, Manfara and Sikara. The zones for large site amplification values (∼3 times) are found at Tapar,
Chopadwa, Adhoi and Chobari. The estimated site response values show a good correlation with the distribution of geological
formations as well as observed ground deformation in the epicentral zone. 相似文献
7.
—?We have used micro-earthquake recordings (M= 1.8–4.1) of local events in the distance range of 5–60?km in order to quantify the attenuation and site effects in the vicinity of the Bursa city, Marmara region, Turkey. The data set consists of 120 three-component recorded accelograms from 69 earthquakes, recorded at six stations. Each station is deployed on different geologic units, such as massive limestone, slope deposit and Quaternary young sediments, in the framework of the Marmara Poly-Project.¶In this study a nonparametric inversion method was applied to acceleration records from the Bursa region to estimate source, site and path effects using a two-step inversion. At the first step, we determined attenuation functions by analyzing the distance dependence of the spectral amplitudes and retrieved values of Q s (f) = 46.59f 0.67. At the second step, the corrected S-waves spectral records for the attenuation function, including the geometrical spreading effect, were inverted to separate source and site response for 21 different frequencies selected between 0.5 and ~25?Hz. The near-surface attenuation, κ value, was also estimated by using the model proposed by Anderson and Hough (1984) at each site. We observed that κ0 is smaller for stations located on rock site (I?dιr, SIGD, κ0~0.004) compared to the one that is located on Neogene sediment (Çukurca, SCKR, κ0~0.018).¶Site amplifications from inversion showed that the station located within the Bursa basin, Çukurca (SCKR), is the most important site with about 4.0 amplification value at 1.8?Hz. Demirta? (SDEM) amplifies the spectral amplitudes about 3.0 times at 2.0?Hz, SHMK about 3.5 times between 2.5 and 3.5?Hz and SHMT nearly reaching 3.5 times between 1.5 and 4.0?Hz. However, stations located on the Uluda? Mountain Massif (SKAY and SIGD), which correspond to a deep limestone geological unit, have the smallest amplification, that values between 0.6 and 1.4. 相似文献
8.
Jaroslav Střeštík Karel Prikner Karel Dobeš Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1973,17(1):27-35
Summary The spectra of nearly 100 samples of Bpc3 pulsations were computed in the X and Y components of data from the Budkov Observatory. These spectra were used to study the daily variations of the fundamental characteristics of the pulsations, the frequency f
0
and amplitude A
0
of the main spectral peaks. The daily variation of the ellipticity of the polarization ellipses of oscillations in frequency f
0
was also studied in the XY-plane.Part of these results was reported at the XVth General Assembly of the IUGG, Moscow, August 1971. 相似文献
9.
Andrei Bala Bogdan Grecu Viorica Ciugudean Victor Raileanu 《Soil Dynamics and Earthquake Engineering》2009
Bucharest is one of the cities most affected by earthquakes in Europe. Situated at 150–170 km distance from Vrancea epicentral zone, Bucharest had suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8–12 levels, while more than 150 old buildings with 6–9 levels were seriously damaged. The studies done after this earthquake had shown the importance of the surface geological structure upon ground motion parameters. New seismic measurements are performed in Bucharest area aiming at defining better elastic and dynamic properties of the shallow sedimentary rocks. Down-hole seismic measurements were performed in a number of 10 cased boreholes drilled in the Bucharest City area. Processing and interpretation of the data lead to the conclusion that shallow sedimentary rocks can be considered weak in the area, down to 150–200 m depth. Seismic wave velocity values and bulk density values presented in the paper associated with local geology are useful primary data in the seismic microzonation of Bucharest City. They are used as 1D models to derive transfer functions and response spectra for the stack of sedimentary rocks in several parts of Bucharest area, leading to a better knowledge of the local site amplification and associated frequency spectra. In a recent study the H/V spectral ratio using Nakamura’s method was applied on the seismic noise measurements in 22 sites in Bucharest City in order to derive the fundamental period associated with these sites. The values confirm the previous results, showing a dominant resonance in the period range of 1.25–1.75 s. The fundamental periods obtained with Nakamura’s method are in good agreement with those computed on the basis of geological and geotechnical data in boreholes, which show an increase of the fundamental period in the Bucharest area from south to north, in the same direction as the increase of the thickness of the Quaternary deposits above the Fratesti layer which is considered the bedrock in the area. 相似文献
10.
Cadet Héloïse Anne-Marie Duval Etienne Bertrand 《Bulletin of Earthquake Engineering》2012,10(2):451-489
This paper presents empirical correlations between amplification factors and simple site parameters derived from a large subset
of the KiK-net data. The amplification factor is estimated from the ratios between the surface and down-hole horizontal response
spectra, corrected for the varying depths and impedance of the down-hole sites (Cadet et al. in Site effect assessment using
KiK-net data—part 1—a simple correction procedure for surface/downhole spectral ratios, 2011). Several site parameters are selected on the basis of their simplicity and availability at relatively low cost. They are
the shallow time-average velocities VSZ, with z equal to 5, 10, 20 and 30 m, and the fundamental frequency f0. The amplification factors are then correlated with each of the individual site parameters; four other “twin-parameter”—couples
(f0, VSZ)—are also considered and the correlation with amplification factors is performed through a normalization of the frequencies
by each site fundamental frequency. The quality of the correlations is given by a misfit compared with the original data variance.
The largest variance reduction is obtained with twin-parameter characterizations, out of which the couple (f0, VS30) proves to provide the lower misfit. The performance of single parameter correlations is relatively lower; however, the best
single parameter proves to be the fundamental frequency, which provides smaller misfit than the Vsz parameters. A comparison
is also performed with the amplification factors recommended in European regulations, showing that it is possible right now
to significantly improve both the site characterization criteria and the associated amplification factors, for use in building
codes and microzonation studies. 相似文献
11.
Based on spectral ratio method, a joint inversion method was used to obtain parameters of Lg wave attenuation and site response. The inversion method allows simple and direct (two-parameter) determination of Lg wave attenua- tion and site response from sparse spectral data, which are not affected by radiation pattern factor and different response of same instrument after geometrical spreading. The method was used successfully for estimating site re- sponse of stations of Zhejiang Seismic Network and measuring Lg wave attenuation. The study is based on 20 earth- quakes occurred in northeast of Taiwan with magnitude MS5.0~6.7 and 960 seismic wave records from 16 stations in Zhejiang area from 2002 to 2005. The parameters of site response and Lg attenuation were calculated with a fre- quency interval of 0.2 Hz in the range of 0.5 Hz to 10 Hz. Lg wave attenuation coefficient corresponding to U-D, E-W and N-S components are γ ( f )=0.00175 f 0.43485, γ ( f )=0.00145f 0.48467 and γ ( f )=0.0021f 0.41241, respectively. It is found that the site response is component-independent. It is also found that the site response of QIY station is significant above the frequency of 1.5 Hz, and that the site response of NIB station is low for most frequency 相似文献
12.
The Effect of Velocity Inversions on H/V 总被引:2,自引:0,他引:2
We analyzed the phenomenology of microtremor H/V curves under inversions in the shear-wave velocity (Vs) profile in the subsoil. Under no Vs inversion the spectral signature of the H/V peaks is found to be ‘eye-shaped’ with the horizontal components higher than
the vertical. Conversely, under negative velocity gradients, numerous of differences emerge. I) A H/V ratio below 1 is observed
for a wide range of frequencies, due to the decrease of the horizontal components below the vertical one. II) In the presence
of persistent H/V < 1, small bumps in the H/V ratio given by local minima in the vertical spectral component may represent
the relics of the peaks indicating resonances and stratigraphic discontinuities. As a consequence, in the presence of velocity
inversions the H/V > 2 SESAME (2004) criterion fails but a stratigraphic interpretation may still be possible. III) The H/V
curves should always be interpreted together with the single component spectra. IV) Microtremor H/V measurements for stratigraphic/microzonation purposes on stiff artificial
soils, (asphalt, concrete, cement, pavements) should always be avoided since the latter often produce velocity inversions.
This may have consequences in the intermediate to high frequency domain ( > 1 Hz) also in the application of reference site
methods, like Hsite/Hbedrock, to microtremor. Theoretical modeling confirms these experimental findings. 相似文献
13.
R. Maresca M. Castellano R. De Matteis G. Saccorotti P. Vaccariello 《Pure and Applied Geophysics》2003,160(9):1745-1764
14.
为了克服广义线性反演方法(GIT)中理想的参考场地难以找到的局限性,本文将四分之一波长法计算的平均场地放大系数和谱衰减法计算的高频衰减参数作为GIT方法的经验参考场地(ERS)。以2008年5月至8月间28个强震动台站记录的95个汶川8.0级地震余震的615组强震动记录为例,通过与其他方法的比较,验证了ERS-GIT的合理性,并讨论了各类方法之间差异的原因。结果显示,ERS-GIT方法、传统GIT方法和非参数化GIT方法计算得到的平均应力降依次为1.15 MPa,0.78 MPa和0.52 MPa;ERS-GIT方法和传统GIT方法得到的品质因子分别为Q(f)=75.02f1.27和Q(f)=65.56f1.22。以场地的卓越频率为分界,ERS-GIT方法得到的局部场地响应在长周期和高频部分分别与H/V谱比法和传统GIT方法更为接近。 相似文献
15.
G. Ameri A. Oth M. Pilz D. Bindi S. Parolai L. Luzi M. Mucciarelli G. Cultrera 《Bulletin of Earthquake Engineering》2011,9(3):717-739
We exploit S-wave spectral amplitudes from 112 aftershocks (3.0 ≤ ML ≤ 5.3) of the L’Aquila 2009 seismic sequence recorded at 23 temporary stations in the epicentral area to estimate the source
parameters of these events, the seismic attenuation characteristics and the site amplification effects at the recording sites.
The spectral attenuation curves exhibit a very fast decay in the first few kilometers that could be attributed to the large
attenuation of waves traveling trough the highly heterogeneous and fractured crust in the fault zone of the L’Aquila mainshock.
The S-waves total attenuation in the first 30 km can be parameterized by a quality factor QS(f) = 23f
0.58 obtained by fixing the geometrical spreading to 1/R. The source spectra can be satisfactorily modeled using the omega-square
model that provides stress drops between 0.3 and 60 MPa with a mean value of 3.3±2.8 MPa. The site responses show a large
variability over the study area and significant amplification peaks are visible in the frequency range from 1 to more than
10 Hz. Finally, the vertical component of the motion is amplified at a number of sites where, as a consequence, the horizontal-to-vertical
spectral ratios (HVSR) method fails in detecting the amplitude levels and in few cases the resonance frequencies. 相似文献
16.
—?Four days after the December 13, 1990 Hualien, Taiwan earthquake (M L = 6.9), a temporary array of fifteen triaxial digital accelerographs was deployed in the epicenter area to monitor aftershocks. Approximately 600 earthquakes triggered this array during the three-month deployment period. The Yan-Liau station (S63) alone recorded 162 events. Most of the accelerograms at S63 exhibit resonance. We have estimated site responses at the Yan-Liau station using both the single-station spectral ratio (or H/V ratio) method and the traditional spectral ratio method that compares ratios at a soil site with those at a reference hard rock site. Based on site response analyses of S waves and coda waves of ground motion recordings, both types of waves show that the H/V ratio provide a good estimate at the resonant frequency although the site amplification factor is overestimated. In addition, the study of microtremor is also a good alternate for estimating the site predominant frequency. While the ground acceleration (or PGA) gradually increases, the resonant frequency shifts to lower frequencies. 相似文献
17.
K. Prikner 《Annales Geophysicae》1996,14(7):699-706
Three series of simultaneous pulsation measurements (f<0.06 Hz) on the Freja satellite and at the Budkov Observatory have been spectrally processed (FFT) in 6-min intervals of Freja’s transits near the local Budkov field line. Doppler-shifted, weighted spectral-peak frequencies, determined in both transverse magnetic components in the mean field-aligned coordinate system on Freja, allowed the estimation, by comparison with the stable frequency at Budkov, of fundamental frequencies of the local magnetic-field-line resonance ranged from 13 to 17 mHz in two pulsation events analyzed, with Kp=2+ to 0+. The ratio of total amplitudes of the spectral-pulsation components on the ground and on Freja at an altitude of \sim1700 km (values <0.7) characterizes the transmissivity of the ionosphere. In the Pc3 frequency range this correlates well with simulation computations using models of the ionosphere under low solar activity. 相似文献
18.
Sorption behavior of phenanthrene in Yangtze estuarine sediments: sequential separation 总被引:1,自引:0,他引:1
In the present study, phenanthrene was chosen as the probe compound for determining the sorption of PAHs in sediments from Yangtze estuary and nearby coastal area, China. Sorption isotherms were fitted well by the Freundlich and dual models, respectively. Selected sediments were further sequentially separated to remove the carbonate and organic carbon (OC). Calculated OC sorption capacity values based on both H2O2 oxidization and 375 °C combustion methods were similar and comparable to the Koc values estimated by the empirical linear sorption equations. Both sorption models and sorption data using sequentially separated samples achieve the similar conclusions: (1) the partition behavior dominated by OC in sediments with foc > 0.01; (2) for sediments with 0.001 < foc < 0.01, OC dominated sorption at relatively high aqueous concentration; whereas mineral phase adsorption dominated sorption at lower concentration especially when Cw/Sw was in the range of 0.0001-0.001 in natural aqueous system. 相似文献
19.
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
20.
Stefano Parolai Gottfried Grünthal Rutger Wahlstrm 《Soil Dynamics and Earthquake Engineering》2007,27(1):49-59
Seismic noise was measured at some 20 sites in the Cologne area (Germany) aligned nearly perpendicular to a graben structure. The H/V spectral noise ratio for each site was used to derive realistic S-wave velocity profiles down to the bedrock by means of a genetic algorithm inversion. Numerical simulations were performed for different combinations of source and propagation path parameters: focal depth, epicentral distance, attenuation and fault mechanism. Synthetic seismograms were produced and converted to Fourier and response spectra. Finally, the site-specific values from response spectral ratios, with their uncertainties, were used to modify attenuation functions entering the logic-tree algorithm of the probabilistic seismic hazard assessment (PSHA). The site-specific response spectra show the significance of taking into account the local S-wave velocity structure in PSHA. 相似文献