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1.
Twenty six sites were instrumented in the city of Vartholomio following the December 2, 2002 Ms 6.0 earthquake. Thirty weak events from the aftershock sequence as well as microtremors were used to identify amplifications due to geological site effects. Horizontal-to-vertical spectral ratios (HVSR—Nakamura estimates) and weak events ratios were calculated and the singular spectrum analysis (SSA) method was used. The results showed that the effects of SSA on the stability of the frequency peak and amplitude distribution of HVSR for both weak motion and microtremors. The data analysis confirms the role of near surface geology in causing locally significant variations of the predominant frequencies and amplitudes of ground shaking as already inferred from the distribution of damages. The site response spectra exhibited significant peaks within the range of 1.5–2.6 Hz and the amplification factor did not exceed 6.5. Finally the parts of the HVSR ratios from ～0.2 up to 10 Hz were used, in order to create an automatic optimal zonation of the study area using a genetic algorithm. This procedure resulted in the division of the city into 2 main zones.  相似文献   

2.
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   

3.
Seven sites were instrumented in the Parsa area located in the seismically active Dead Sea rift system. Moderate and weak motions generated by earthquakes and ambient noise were used to identify amplifications due to geological and topographic effects.Three observation methods were applied to estimate site effects: (1) conventional soil–bedrock station-pair spectral ratios for earthquake motions and microtremors; (2) horizontal-to-vertical component spectral ratios for shear-waves observed simultaneously at a site (receiver function estimates) and (3) horizontal-to-vertical spectral ratios of microtremor measurements (Nakamura estimate). The site response spectra of soil sites exhibited significant peaks between 1 and 3 Hz with amplification factors typically within the range of 2.5–4.0. A bedrock site on the high plateau near the escarpment top showed a peak between 2 and 3 Hz, mainly due to an EW oscillation of the NS topographic feature. Our observations indicated that seismograms recorded in the tunnel were either enriched or depleted at certain frequencies owing to interference of incident and surface-reflected waves.  相似文献   

4.
Empirical evaluation of microtremor H/V spectral ratio   总被引：6，自引：2，他引：4  
The objective of this work is to perform a purely empirical assessment of the actual capabilities of the horizontal-to-vertical (H/V) spectral ratio technique to provide reliable and relevant information concerning site conditions and/or site amplification. This objective has been tackled through the homogeneous (re)processing of a large volume of earthquakes and ambient noise data recorded by different research teams in more than 200 sites located mainly in Europe, but also in the Caribbean and in Tehran. The original recordings were first gathered in a specific database with information on both the sites and recorded events. Then, for all sites close to an instrumented reference, average site-to-reference spectral ratios (“spectral ratio method” (SSR)) were derived in a homogeneous way (window selection, smoothing, signal-to-noise ratio threshold, averaging), as well as H/V ratios (“HVSRE–RF”) on earthquake recordings. H/V ratios were also obtained from noise recordings at each site (either specific measurements, or extracted from pre- or post-event noise windows). The spectral curves resulting from these three techniques were estimated reliable for a subset of 104 sites, and were thus compared in terms of fundamental frequency, amplitude and amplification bandwidth, exhibiting agreements and disagreements, for which interpretations are looked for in relation with characteristics of site conditions. The first important result consists in the very good agreement between fundamental frequencies obtained with either technique, observed for 81% of the analyzed sites. A significant part of the disagreements correspond to thick, low frequency, continental sites where natural noise level is often very low and H/V noise ratios do not exhibit any clear peak. The second important result is the absence of correlation between H/V peak amplitude and the actual site amplification measured on site-to-reference spectral ratios. There are, however, two statistically significant results about the amplitude of the H/V curve: the peak amplitude may be considered as a lower bound estimate of the actual amplification indicated by SSR (it is smaller for 79% of the 104 investigated sites), and, from another point of view, the difference in amplitude exhibits a questioning correlation with the geometrical characteristics of the sediment/basement interface: large SSR/HV differences might thus help to detect the existence of significant 2D or 3D effects.  相似文献   

5.
On 6 April 2009 a Mw=6.1 earthquake produced severe destruction and damage over the historic center of L’Aquila City (central Italy), in which the accelerometer stations AQK and AQU recorded a large amount of near-fault ground motion data. This paper analyzes the recorded ground motions and compares the observed peak accelerations and the horizontal to vertical response spectral ratios with those revealed from numerical simulations. The finite element method is considered herein to perform dynamic modeling on the soil profile underlying the seismic station AQU. The subsurface model, which is based on the reviewed surveys that were carried out in previous studies, consists of 200–400 m of Quaternary sediments overlying a Meso-Cenozoic carbonate bedrock. The Martin-Finn-Seed's pore-water pressure model is used in the simulations. The horizontal to vertical response spectral ratio that is observed during the weak seismic events shows three predominant frequencies at about 14 Hz, 3 Hz and 0.6 Hz, which may be related to the computed seismic motion amplification occurring at the shallow colluvium, at the top and base of the fluvial-lacustrine sequence, respectively. During the 2009 L’Aquila main shock the predominant frequency of 14 Hz shifts to lower values probably due to a peculiar wave-field incidence angle. The predominant frequency of 3 Hz shifts to lower values when the earthquake magnitude increases, which may be associated to the progressive softening of soil due to the excess pore-water pressure generation that reaches a maximum value of about 350 kPa in the top of fluvial-lacustrine sequence. The computed vertical peak acceleration underestimates the experimental value and the horizontal to vertical peak acceleration ratio that is observed at station AQU decreases when the earthquake magnitude increases, which reveals amplification of the vertical component of ground motion probably due to near-source effects.  相似文献   

6.
The effect of soil inhomogeneity and material nonlinearity on kinematic soil–pile interaction and ensuing bending under the passage of vertically propagating seismic shear waves in layered soil, is investigated by means of 1-g shaking table tests and nonlinear numerical simulations. To this end, a suite of scale model tests on a group of five piles embedded in two-layers of sand in a laminar container at the shaking table facility in BLADE Laboratory at University of Bristol, are reported. Results from white noise and sine dwell tests were obtained and interpreted by means of one-dimensional lumped parameter models, suitable for inhomogeneous soil, encompassing material nonlinearity. A frequency range from 0.1 Hz to 100 Hz and 5 Hz to 35 Hz for white noise and sine dwell tests, respectively, and an input acceleration range from 0.015 g to 0.1 g, were employed. The paper elucidates that soil nonlinearity and inhomogeneity strongly affect both site response and kinematic pile bending, so that accurate nonlinear analyses are often necessary to predict the dynamic response of pile foundations.  相似文献   

7.
Local Site Effects in the Town of Benevento (Italy) from Noise Measurements   总被引：2，自引：0，他引：2  
— The study of ground motion amplification produced by surface geology is extremely interesting in the Benevento area, Southern Italy, as it is characterized by high seismic hazard. The present moderate-to-low seismicity makes the noise method appropriate to estimate the seismic site response in the area. The three components of seismic noise have been recorded in five sites in the Benevento metropolitan area characterized by different surface geology, in order to estimate the seismic site response. In evaluating site amplification effects we used the direct interpretation of amplitude spectra and standard spectral ratio techniques, evaluating sediment-to-bedrock, sediment-to-average and H/V spectral ratios. The temporal evolution of the noise spectra is analysed within one day, in order to assess the stationarity of the noise signal. The noise wavefield properties have been studied through polarization analyses in selected bands of frequency, where spectral peaks are observed to dominate, to better understand the real nature of those peaks. Results give evidence of low amplification levels, missing any correlation between spectral amplitudes and sediment thickness over the basement. We interpret this result as due to the poor impedance contrast between sediments and basement, which is characterized by low values of shear waves velocity. Moreover, sharp amplitude peaks are observed in the raw spectra of the sediment-sites, in the 2–4 Hz frequency band; a numerical simulation interprets this effect as possibly associated with a wide-scale structure, invoking the presence of a sharper impedance contrast at greater depth. At high frequencies the action of ambient noise sources, mainly active on horizontal components of motion, is retained dominant to generate the prominent peaks observed in the H/V spectral ratios; in some cases the presence of a near-surface low-velocity layer can contribute to amplify the seismic motion generated at these frequencies.  相似文献   

8.
This paper presents a study of site effects in the urban area of Tecoman in Colima, Mexico. A variety of instruments (both accelerometers and seismometers) were used to record earthquakes and ambient vibration throughout the city. Earthquake records were analysed using several techniques to estimate site effects: spectral ratios relative to a reference station, spectral ratios of the horizontal components relative to the vertical recorded at the same site, and a parametric inversion of Fourier spectra. Ambient noise records were used to estimate a local transfer function using horizontal to vertical spectral ratios. The results show that local amplification at Tecoman is significant. Dominant frequency varies between 0.5 and 0.7 Hz, suggesting a large thickness of the soft sedimentary deposits. We did not observe systematic variations throughout the city. Our more reliable estimates indicate that maximum amplification is comprised between a factor 6 and 8. Comparisons among different sensors and recorders show that all combinations between velocimeters, accelerometers, and recorders provide reliable results provided that the electronic noise is smaller than the noise being recorded. This is notably not the case for accelerometers at quiet sites and for frequencies smaller than 2 Hz. This explains why previous studies disagree as to the usefulness of accelerometers to record ambient noise for site effect studies. This factor is, however, a function of noise amplitude at each site.  相似文献   

9.
The ground track of the annular eclipse of 3 October 2005 crossed the Iberian Peninsula. The main objective of this work was to analyze the variability of the solar irradiance and the total ozone column during the course of this event at El Arenosillo (Southwestern Spain). For achieving this goal, two Kipp & Zonen broadband radiometers (one for measuring total solar irradiance and other for measuring ultraviolet erythemal solar irradiance), one NILU-UV multi-band instrument and one Brewer spectroradiometer were used in this work. Total irradiance (310–2800 nm), and ultraviolet erythemal radiation (UVER) were recorded at a high frequency of 5 s, showing a strong reduction (higher than 80%) of the irradiance at the maximum solar obscuration which was of 79.6%. The irradiance decrease during the course of the eclipse was positively correlated with the percentage of eclipse obscuration, showing a very high agreement (R2～0.99). The irradiance recorded at selected wavelengths from the NILU-UV instrument shows a more pronounced decrease in the UV irradiance at the lower wavelengths during the solar eclipse. Finally, the evolution of the total ozone column (TOC) derived from Brewer and NILU instruments during the eclipse presented an opposite behavior: while the Brewer derived TOC values increase about 15 DU, the NILU derived TOC values decrease about 11 DU. This opposite behavior is mainly related to an artifact in the spectral irradiances recorded by the two instruments.  相似文献   

10.
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   

11.
A field measurement of ground vibration was performed on the Beijing−Shanghai high-speed railway in China. In this paper, the experimental results of vertical ground vibration accelerations induced by very high speed trains running over a non-ballasted track on embankment with speeds from 300 to 410 km/h are reported and analyzed in detail for the first time. Characteristics of ground vibration accelerations in both time and frequency domains are analyzed based on the test data. It is shown that the periodic exciting action of high-speed train bogies can be identified in time histories of vertical accelerations of the ground within the range of 50 m from the track centerline. The first dominant sensitive frequency of the ground vibration acceleration results from the wheelbase of the bogie, and the center distance of two neighboring cars plays an important role in the significant frequencies of the ground vibration acceleration. Variations of time–response peak value and frequency-weighted vertical acceleration level of ground vibration in relation with train speed as well as the distance from the track centerline are also investigated. Results show that the time-domain peak value of ground vibration acceleration exhibits an approximately linear upward tendency with the increase of train speed. With the increasing distance from the track centerline, the frequency-weighted vertical acceleration level of the ground vibration attenuates more slowly than the time-domain peak value of the ground vibration acceleration does. Severe impact of high-speed railway ground vibration on human body comfort on the ground occurs at the speed of 380–400 km/h. The results given in the paper are also valuable for validating the numerical prediction of train induced ground vibrations.  相似文献   

12.
Soil–structure interaction (SSI) effects on building dynamic behaviour have been studied extensively. In comparison, the radiation of waves away from the soil–foundation interface has received little attention. Recent studies point out that SSI in an urban environment can modify the ground motion recorded in the free-field. These modifications will be important when two conditions are met: structures founded on soft soils and coincidence between the vibration periods of the structure and those of the superficial layers. Both conditions are met in Mexico City lake zone. In this study, we investigate SSI effects on ‘free-field’ motion. The data we use consist of microtremors recorded on soft soils in Mexico City, a densely built environment. Our objective was to identify the modifications to free-field ground motion caused by neighbouring structures. Data were analysed using H/V spectral ratios. Large variations in the level of amplification and resonant frequency were determined from microtremors in very closely spaced stations. Our results suggest consistently that free-field ground motion is significantly affected by the presence of neighbouring structures.  相似文献   

13.
In Ottawa, Canada, unusually high amplification ratios have recently been measured in clayey silts (called ‘Leda Clays’) at low levels of earthquake-induced ground shaking. However, the contribution of seismic Q, or material damping (ξ=1/2Q), to the overall ground motion at soft soil sites across the city is not well understood. This research investigates attenuation measurements in soft soils (Vs<250 m/s) for ongoing seismic hazard evaluation in the Ottawa area. The work focuses on in situ measurements of damping in two deep boreholes drilled into Leda Clay. To investigate the possibility of frequency-dependent dynamic properties of these materials at low strains, a new approach to the spectral ratio technique has been developed for the measurement of Qs in the field using a mono-frequency vibratory source (generating signals between 10 and 100 Hz), and two identical downhole 3-component geophones. Monofrequency signals also allowed for the measurement of dispersion (variation of velocity with frequency). Analysis of the data show that dynamic properties are, for the most part, independent of frequency in the homogenous silty soils, yielding negligible variation in shear wave velocity (<2 m/s) across the frequency test band, and small strain Qs's ranging from 170 to 200 (damping of 0.25–0.30%) over soil thickness intervals ranging from 10 to 60 m. At intervals within 20 m of the ground surface, laminated silt and clay beds of elevated porosity are found to have slight influence on the frequency dependence of damping for frequencies greater than 70 Hz (damping increase to 0.6%).  相似文献   

14.
An experimental development of a computer controlled photoelectric ocular system applied for the LaCoste and Romberg G949 gravimeter made the continuous observation of time variation of gravity possible. The system was operated for half a year in the Sopronbánfalva Geodynamical Observatory to test its capabilities. The primary aim of this development was to provide an alternative and self-manageable solution instead of the standard electronic (Capacitive Position Indicator) reading of this type of gravimeter and use it for the monitoring of Earth tide. It, however, turned out that this system is sensitive enough to observe the effect of variable seismic noise (microseisms) due to the changes of ocean weather in the North Atlantic and North Sea regions at microGal level (1 μGal = 10−8 m/s2). Up to now not much attention was paid to its influence on the quality and accuracy of gravity observations because of the large distance (>1000 km) between the observation place (generally the Carpathian–Pannonian basin) and the locations (centres of storm zones of the northern hydrosphere) of triggering events. Based on an elementary harmonic surface deformation model the noise level of gravity observations was compared to the spectral characteristics of seismic time series recorded at the same time in the observatory. Although the sampling rate of gravity records was 120 s the daily variation of gravity noise level showed significant correlation with the variation of spectral amplitude distribution of the analysed high pass filtered (cut-off frequency = 0.005 Hz) seismograms up to 10 Hz. Also available daily maps of ocean weather parameters were used to support both the correlation analysis and the parameterization of the triggering events of microseisms for further statistical investigations. These maps, which were processed by standard image processing algorithms, provide numerical data about geometrical (distance and azimuth of the storm centres relative to the observation point) and physical (mass of swelling water) quantities. The information can be applied for characterizing the state of ocean weather at a given day which may help the prediction of its influence on gravity measurements in the future. Probably it is the first attempt to analyse quantitatively the effect of ocean weather on gravity observations in this specific area of the Carpathian–Pannonian region.  相似文献   

15.
Shipping noise is a threat to marine wildlife. Grey seals are benthic foragers, and thus experience acoustic noise throughout the water column, which makes them a good model species for a case study of the potential impacts of shipping noise. We used ship track data from the Celtic Sea, seal track data and a coupled ocean-acoustic modelling system to assess the noise exposure of grey seals along their tracks. It was found that the animals experience step changes in sound levels up to ~ 20 dB at a frequency of 125 Hz, and ~ 10 dB on average over 10–1000 Hz when they dive through the thermocline, particularly during summer. Our results showed large seasonal differences in the noise level experienced by the seals. These results reveal the actual noise exposure by the animals and could help in marine spatial planning.  相似文献   

16.
Horizontal-to-vertical spectral ratios (HVSR) of ambient vibrations measured in the ancient town of Ston (Croatia) on 99 locations, are shown to be well matched to the theoretical ones computed for body-waves as well as for the surface waves. This match is poorer for sites on the slopes of nearby hills. The ratios of measured peak horizontal ground acceleration during the damaging earthquake in 1996 (M L = 6.0) and the ones obtained using empirical attenuation laws is approximately equal to the mapped value of the dynamic amplification factor determined on the basis of observed HVSR in the vicinity of the accelerometric station. The HVSR of the accelerogram is very similar to the HVSR of the ambient noise. The damage to the building stock in the old town centre caused by the earthquake series of 1996 is closely related to the estimated soil amplification and its fundamental frequency. More measurements in buildings are needed to arrive at confident conclusions about possible soil-structure resonance.  相似文献   

17.
A grid of previously unpublished, vintage 2D marine seismic lines has been processed and interpreted to the east of Hanö Bay, SW Baltic Sea. The 3200 km2 study area lies on the transition between the Hanö Bay Basin to the West and Baltic Synelcise to the East, NE of the Tornquist intra shield tectonic zone.Data from the NA79, NA80 and RW84 surveys were selected for this study from the extensive Oljeprospektering AB (OPAB) Baltic Sea dataset. New processing workflows have been developed for the data which focus on suppressing two significant forms of noise, namely multiple and side scattered noise. Deconvolution in the tau-p domain, parabolic radon demultiple and post stack deconvolution are shown to be effective at attenuating multiple noise, while FK filtering in shot and receiver gathers is effective at removing side scattered noise.The newly processed data were interpreted and a series of maps detailing the structure of the basement, Cambrian and Silurian/Paleozoic horizons were constructed. These maps differ significantly to previously published interpretations of the area. Within the study area, a region of significant Late Carboniferous/Early Permian transtensional faulting and Late Cretaceous inversion is mapped in detail. This structure would have exhibited normal offsets of up to 600 m before inversion with later inverted displacements of up to approximately 200 m in places. This feature appears to extend some 20 km to the SW of the study area to the major fault bounding the Christiansø High. Based on the seismic interpretation, the area appears to have had a similar overall geological history as the adjacent Tornquist Zone to the SW.  相似文献   

18.
A temporary seismic network composed of 11 stations was installed in the city of Potenza (Southern Italy) to record local and regional seismicity within the context of a national project funded by the Italian Department of Civil Protection (DPC). Some stations were moved after a certain time in order to increase the number of measurement points, leading to a total of 14 sites within the city by the end of the experiment. Recordings from 26 local earthquakes (Ml 2.2−3.8 ) were analyzed to compute the site responses at the 14 sites by applying both reference and non-reference site techniques. Furthermore, the Spectral Intensity (SI) for each local earthquake, as well as their ratios with respect to the values obtained at a reference site, were also calculated. In addition, a field survey of 233 single station noise measurements within the city was carried out to increase the information available at localities different from the 14 monitoring sites. By using the results of the correlation analysis between the horizontal-to-vertical spectral ratios computed from noise recordings (NHV) at the 14 selected sites and those derived by the single station noise measurements within the town as a proxy, the spectral intensity correction factors for site amplification obtained from earthquake analysis were extended to the entire city area. This procedure allowed us to provide a microzonation map of the urban area that can be directly used when calculating risk scenarios for civil defence purposes. The amplification factors estimated following this approach show values increasing along the main valley toward east where the detrital and alluvial complexes reach their maximum thickness.  相似文献   

19.
The error properties of arrays of accelerometers were studied on the basis of systematic experiments and analysis of the differences in the recordings of collocated sensors. Four identical tri-axial force-balance accelerometers with common recordings and time stamping, were set at symmetrical positions on a prototype oscillator, a T-type inverted pendulum, and were subject to controlled excitations. Based on Finite Element Modeling (FEM) the response of the oscillator was modeled and there were identified time series of acceleration of different collocated sensors predicted to be identical (“comparable”). The differences of the corresponding “comparable” measurement time series, which are functions only of noise, were found important, indicating that the accelerometer arrays are characterized by significant dynamic noise and not by low-amplitude Gaussian noise, as is widely assumed.Further analysis of time series of accelerometer noise was based on spectral analysis techniques in the frequency and the time domain and on coherence, on filtering and on cross-correlation, as well as on examination of the impact of noise in the drift (errors computation of displacements using double numerical integration).The output of this study is that phase noise (jitter, or phase instability) characterizes accelerometers, as in the case with all other array sensors and sensor networks and this is a main source of dynamic noise. The latter becomes significant especially at the level of sampling interval (0.005 sec in our experiments), characterizes strong motions, is not constant and may be regarded as instrument-specific noise. Strategies to overcome this dynamic noise important for the modeling of structural response are discussed.  相似文献   

20.
The authors examine the reliability of site response estimations obtained by the horizontal to vertical (H/V) spectral ratios of microtremors by means of cross‐validation with the ratio of the horizontal spectra of earthquake motion with respect to reference sites. The data comprise microtremor and ground motion records recorded at 150 sites of Yokohama strong motion array. The use of non‐supervised pattern recognition techniques aims to group the sites with more objectivity. Attributes defining the overall shape of the amplification spectra serve as input in the computation of Euclidean distance similarity coefficients amongst sites. The implementation of the Ward clustering scheme leads to the attainment of a meaningful tree diagram. Its analysis shows the possibility of summarizing the results into six general patterns. A good coincidence of site effects estimates at 80 per cent of the sites becomes apparent. However, this coincidence appears poor for sites characterized by H/V amplification ratios around 2 or smaller and predominant periods longer than 0.5 s. In such cases, the presence of stiff, sandy sediments in the soil profile proves common. To proscribe H/V estimations, relying solely on the small spectral ratios criterion seems inadequate. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

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