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1.
The most commonly used intensity measure in ground-motion prediction equations is the pseudo-absolute response spectral acceleration (PSA), for response periods from 0.01 to 10 s (or frequencies from 0.1 to 100 Hz). PSAs are often derived from recorded ground motions, and these motions are usually filtered to remove high and low frequencies before the PSAs are computed. In this article we are only concerned with the removal of high frequencies. In modern digital recordings, this filtering corresponds at least to an anti-aliasing filter applied before conversion to digital values. Additional high-cut filtering is sometimes applied both to digital and to analog records to reduce high-frequency noise. Potential errors on the short-period (high-frequency) response spectral values are expected if the true ground motion has significant energy at frequencies above that of the anti-aliasing filter. This is especially important for areas where the instrumental sample rate and the associated anti-aliasing filter corner frequency (above which significant energy in the time series is removed) are low relative to the frequencies contained in the true ground motions. A ground-motion simulation study was conducted to investigate these effects and to develop guidance for defining the usable bandwidth for high-frequency PSA. The primary conclusion is that if the ratio of the maximum Fourier acceleration spectrum (FAS) to the FAS at a frequency $f_{saa} $ corresponding to the start of the anti-aliasing filter is more than about 10, then PSA for frequencies above $f_{saa} $ should be little affected by the recording process, because the ground-motion frequencies that control the response spectra will be less than $f_{saa} $ . A second topic of this article concerns the resampling of the digital acceleration time series to a higher sample rate often used in the computation of short-period PSA. We confirm previous findings that sinc-function interpolation is preferred to the standard practice of using linear time interpolation for the resampling. 相似文献
2.
J. Douglas 《Bulletin of Earthquake Engineering》2003,1(1):141-156
Some accelerograms are affected by non-standard recording and digitization problems that mean they are often not used in strong-motion
studies. These non-standard problems cannot be corrected by the standard processing techniques that remove low and high-frequency
noise from the time-history. Records from analogue instruments are more prone to these problems but even records from digital
instruments, which are becoming increasingly common, can be affected by such errors. Since all strong-motion data is valuable
it is important to know whether any useful information can be obtained from accelerograms that are affected by such problems.
This article examines whether strong-motion records from analogue instruments that are missing their initial part due to late
triggering of the instrument and also strong-motion records from digital instruments with low A/D converter resolution can
be used for response spectral studies. It is found, by simulating such errors on high-quality strong-motion records, that
good response spectral ordinates can be obtained from such `poor-quality' records within the period range of most engineering
interest.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Ground-motion prediction equations (GMPEs) for spectral accelerations have traditionally focused on the range of response
periods most closely associated with the dynamic characteristics of buildings. Providing predictions only in this period range
(from 0.1 to 2 or 3 s) has also accommodated the assumed limitations on the usable period range resulting from the processing
of accelerograms. There are, however, engineering applications for which estimates of spectral ordinates are required at shorter
response periods. Recent work has demonstrated that high-frequency spectral ordinates are relatively insensitive to record
processing, contrary to previous assumptions. In the light of this finding, additional regressions are performed to extend
a recent pan-European GMPE to higher response frequencies. This model and others that also include coefficients for spectral
ordinates at several high response frequencies are used to explore options for interpolating coefficients for equations that
do not provide good coverage in this range. The challenges and uncertainties associated with such interpolations are discussed.
The paper concludes that a set of standard response frequencies could be usefully established for future GMPEs. 相似文献
4.
The range of response frequencies for which spectral ordinates obtained from accelerograms may be considered reliable is limited by several factors, primary among them being the effects of filters that are routinely applied to remove noise from the records. Considerable attention has been focused on the low‐frequency limit of the usable spectral ordinates because of various engineering applications requiring long‐period spectral accelerations or displacements but only recently have rational approaches to selecting the high‐frequency limit been proposed. Since there are applications for which the high‐frequency spectral ordinates are important, the approaches to this issue presented in the recent studies are reviewed and their application to the ground‐motion database from Europe and the Middle East is explored. On the basis of the results of these analyses, it is concluded that a large proportion of this dataset can be used to provide reliable estimates of response spectral ordinates at much shorter periods than may have previously been considered feasible. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
5.
R. Puglia R. Ditommaso F. Pacor M. Mucciarelli L. Luzi M. Bianca 《Bulletin of Earthquake Engineering》2011,9(3):869-892
Previous works based mainly on strong-motion recordings of large Japanese earthquakes showed that site amplification and soil
fundamental frequency could vary over long and short time scales. These phenomena were attributed to non-linear soil behaviour:
the starting fundamental frequency and amplification were both instantaneously decreasing and then recovering for a time varying
from few seconds to several months. The recent April 6, 2009 earthquake (M
W 6.3), occurred in the L’Aquila district (central Italy), gave us the possibility to test hypotheses on time variation of
amplification function and soil fundamental frequency, thanks to the recordings provided by a pre-existing strong-motion array
and by a large number of temporary stations. We investigated the intra- and inter-event soil frequency variations through
different spectral analyses, including time-frequency spectral ratios and S-Transform (Stockwell et al. in IEEE Trans Signal
Process 44:998–1001, 1996). Finally, analyses on noise recordings were performed, in order to study the soil behaviour in linear conditions. The results
provided puzzling evidences. Concerning the long time scale, little variation was observed at the permanent stations of the
Aterno Valley array. As for the short time-scale variation, the evidence was often contrasting, with some station showing
a time-varying behavior, while others did not change their frequency with respect to the one evaluated from noise measurements.
Even when a time-varying fundamental frequency was observed, it was difficult to attribute it to a classical, softening non-linear
behaviour. Even for the strongest recorded shocks, with peak ground acceleration reaching 0.7 g, variations in frequency and
amplitude seems not relevant from building design standpoint. The only exception seems to be the site named AQV, where the
analyses evidence a fundamental frequency of the soil shifting from 3 Hz to about 1.5 Hz during the mainshock. 相似文献
6.
Current empirical ground-motion prediction equations for Europe and their application to Eurocode 8 总被引:1,自引:1,他引:0
The first ground-motion prediction equation derived from European and Middle Eastern strong-motion data was published more
than 30 years ago; since then strong-motion networks and the resulting databank of accelerograms in the region have expanded
significantly. Many equations for the prediction of peak ground-motion parameters and response spectral ordinates have been
published in recent years both for the entire Euro-Mediterranean and Middle Eastern region as well as for individual countries
within this region. Comparisons among empirical ground-motion models for these parameters, developed using large regional
datasets, do not support the hypothesis of there being significant differences in earthquake ground-motions from one area
of crustal seismicity to another. However, there are certain regions within Europe—affected by different tectonic regimes—for
which the existing pan-European equations may not be applicable. The most recent European equations make it possible to now
implement overdue modifications to the presentation of seismic design actions in Eurocode 8 that allow an improved approximation
to the target uniform hazard spectrum (UHS). Using these recent equations, this study outlines a new approach via which an
approximation to the UHS may be constructed using hazard maps calculated for peak ground velocity and the corner period T
D in addition to the maps for peak ground acceleration that underpin the current stipulations of Eurocode 8. 相似文献
7.
M. D. Trifunac 《地震工程与结构动力学》1995,24(8):1113-1130
The currently available empirical scaling laws for estimation of spectral amplitudes are limited to periods longer than 0–04 s. However, for design of equipment and stiff structures on multiple and distant supports, exposed to strong shaking near faults where peak accelerations can exceed 1g, specification of design ground motions at higher frequencies is required. This paper presents a method for extrapolation of pseudo-relative velocity spectral amplitudes of strong earthquake shaking to short periods (0–01 < T < 0–04 sec). The extrapolated spectra can be used as a physical basis for defining design spectral amplitudes in this higher-frequency range. The analysis in this paper implies that for typical strong motion accelerations, particularly on sedimentary sites in California, the peak ground accelerations are projected to be unaffected by frequencies higher than those recorded. Consequently, in California, the high-frequency pseudo-acceleration spectra can be approximated from the recorded absolute peak accelerations. 相似文献
8.
The free-field accelerograms along Feitsui Canyon are analyzed and modeled by a numerical scheme to study the effect of canyon topography. Since six strong-motion accelerometers (SC1–SC6) were deployed along the Feitsui Canyon in 1991; there are 14 earthquakes (4.9≤ML≤6.6) recorded by these stations until June 1996, but only five triggered all six stations. The maximum PGA value is 68.6 cm s−2 recorded at station SC1. According to the present data, the effect of the dam on the ground motions at canyon stations can be negligible. The amplitude of ground motion on the slopes of the canyon is bigger than that at its trough. The integral equation method is applied to a two dimensional model of Feitsui Canyon to study the effects of the canyon topography. We choose the ground motion of SC3 or SC4 station at the trough of the canyon as the input motion for the model, which is then used to predict the ground motion at the other five stations. Apart from the earthquake close to the damsite, the simple model can reproduce the observed accelerations at all frequencies below 4 Hz. Overall, the numerical method can well predict the ground motion along the canyon, although the high-frequency simulation is underestimated. 相似文献
9.
10.
Based on the quarter-wavelength approximation, the frequency-dependent site amplifications, A(f ), at 18 free-field strong-motion stations in and near the Taipei Basin are evaluated from well-logging data. The V
30, which is the average of the S-wave velocities in the topmost 30 m, is a significant factor in classifying the sites. Results
show that the site amplifications at all sites in study are larger than 1 and functions of frequency. Compared with the Haskell
method, the quarter-wavelength approximation is almost an average and a good representation of overall amplifications. It
is noted that the site amplifications evaluated in this study can apply only to frequencies greater than about 1.1 Hz for
class C sites and 3.1 Hz for class D. 相似文献
11.
The determination of seismic amplitude amplification is a fundamental contribution to seismic hazard assessment. While often
only high-frequency amplitude variations (>1 Hz) are taken into account, we analyse broadband waveforms from 0.14 to 8.6 Hz
using a temporary network of 32 stations in and around the earthquake-prone city of Bucharest. Spectral amplitudes are calculated
with an adaptive multiple-taper approach. Across our network (aperture 25 km × 25 km), we find a systematic northwest/southeast-oriented
structural influence on teleseismic P-wave amplitudes from 0.14 to 0.86 Hz that can be explained by constructive interference
in the dipping Cenozoic sedimentary layers. For higher frequencies (1.4–8.75 Hz), more local site effects prevail and can
be correlated partly among neighbouring stations. The transition between systematic and localised amplitude variations occurs
at about 1 Hz. 相似文献
12.
Nasser Laouami Abdennasser Slimani Youcef Bouhadad Jean-Luc Chatelain Ali Nour 《Soil Dynamics and Earthquake Engineering》2006,26(11):991-1003
The Algiers–Boumerdes region has been struck by a destructive magnitude 6.8 (Mw) earthquake on May 21, 2003. The study presented in this paper is based on main shock strong motions from 13 stations of the Algerian accelerograph network. A maximum 0.58g peak ground acceleration (PGA) has been recorded at 20 km from the epicenter, only about 150 m away from a PGA of 0.34g, with both a central frequency around 5 Hz, explained by a strong very localized site effect, confirmed by receiver function technique results showing peaks at 5 Hz with amplitudes changing by a factor of 2. Soil amplifications are also evidenced at stations located in the quaternary Mitidja basin, explaining the higher PGA values recorded at these stations than at stations located on firm soil at similar distances from the epicenter. A fault-related directionality effect observed on the strong motion records and confirmed by the study of the seismic movement anisotropy, in agreement with the N65 fault plan direction, explains the SW–NE orientation of the main damage zone. In the near field, strong motions present a high-frequency content starting at 3 Hz with a central frequency around 8 Hz, while in the far field their central frequency is around 3 Hz, explaining the high level of damage in the 3- to 4-story buildings in the epicentral zone. The design spectra overestimate the recorded mean response spectra, and its high corner frequency is less than the recorded one, leading to a re-examination of the seismic design code that should definitively integrate site-related coefficient, to account for the up to now neglected site amplification, as well as a re-modeling of the actual design spectra. Finally, both the proposed Algerian attenuation law and the worldwide laws usually used in Algeria underestimate the recorded accelerations of the 6.8 (Mw) Boumerdes earthquake, clearly showing that it is not possible to extrapolate the proposed Algerian law to major earthquakes. 相似文献
13.
Broadband (0.05 to 20 s) prediction of displacement response spectra based on worldwide digital records 总被引:6,自引:0,他引:6
A new set of empirical equations for prediction of displacement response spectral ordinates from 20 Hz to T = 20 s is illustrated. The coefficients of the equations were obtained by regressing a dataset based on 1,155 tri-axial digital
and 9 analog accelerometer records from 60 earthquakes worldwide. Long period disturbances in the accelerograms were evaluated
and removed using a very recent method, aimed at preserving the long-period spectral content of the records. Analysis of variance
has disclosed only little evidence for regional dependence of ground motions, while a carefully conducted evaluation of site
effects resulted in clearly differentiated spectral amplification bands associated to the main ground types B, C, and D of
Eurocode 8. Spectral ordinates for vibration periods >5 s were found to scale with magnitude quite consistently with theoretical
scaling from Brune’s model. On the other hand, comparison of results with those yielded by recent prediction models in Europe
and the United States (NGA), indicated that the latter may not be uniformly reliable at long periods. The proposed empirical
equations are easily implemented in computer programs for seismic hazard assessment, being characterized by a simple functional
form and a restricted number of predictor variables.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
14.
R. Sigbjörnsson J. Th. Snæbjörnsson S. M. Higgins B. Halldórsson S. Ólafsson 《Bulletin of Earthquake Engineering》2009,7(1):113-126
This preliminary study aims to investigate a M
w
6.3 earthquake that occurred in South Iceland on Thursday 29 May 2008 at 15:45 UTC. The epicentre was in the Olfus District
between the towns of Selfoss and Hveragerdi. This study examines the data recorded and the damage observed immediately after
the event. Horizontal accelerations of up to 80%g were recorded in the epicentral region and there is visual evidence that
the vertical acceleration exceeded 1 g. The PGA data is compared to a ground motion estimation model developed for the South
Iceland earthquakes in June 2000. In general the basic properties of this event are found to be similar to the characteristics
of the South Iceland earthquakes in June 2000. The duration of strong-motion is short and the intensity attenuates rapidly
with increasing distance. The earthquake action resisted by buildings in the near fault area is inspected through evaluation
of elastic as well as inelastic response spectra. The vast majority of structures seemed to withstand the strong-motion fairly
competently and without significant visual damage due firstly to the low-rise, predominantly reinforced concrete or timber,
style of buildings. Secondly, the short duration of strong-motion contributed to the endurance of structures. 相似文献
15.
F. Cara G. Di Giulio G. P. Cavinato D. Famiani G. Milana 《Bulletin of Earthquake Engineering》2011,9(6):1961-1985
The Fucino basin (Central Italy) is one of the largest intramountain alluvial plain in the Apennines range. It has a tectonic
origin related to the presence of important systems of faults located in its northern and eastern edges. Some of these faults
are still active and capable of generating strong seismic events. Site effects related to the soft soils filling the basin
can be very important. In this paper we show the preliminary results of a seismic network installed in the Fucino area in
order to collect information about site amplification effects and geometry of the basin. We analyze ambient seismic vibrations
and recordings of about 150 local earthquakes mainly related to the seismic sequence of the April 6th 2009 Mw 6.3 L’Aquila
event. Moreover the strongest events of L’Aquila sequence were analyzed at the three permanent strong-motion stations operating
in the area. Using standard spectral techniques we investigate the variation of resonance frequencies within the basin. The
ground motion recorded in the Fucino plain is mainly characterized by strong energy at low-frequencies (f < 1 Hz) affecting both horizontal and vertical components. This is particularly evident for stations deployed in correspondence
of very thick deposits of sedimentary filling, where a significant increase of ground-motion amplitude and duration is likely
caused by locally generated surface waves. The amplification at low-frequencies (<1 Hz) on the horizontal components can reach
up a factor of 10 in comparison to nearby stiff sites. However, we found evidences of seismic amplification phenomena also
for stiff sites surrounding the basin, including stations of the Italian strong motion network. The independent geological
information and the shallow shear-velocity profiles available for the basin can be combined with resonance frequencies for
deriving representative geological sections to be used as base for future numerical 2D–3D modeling of the basin. 相似文献
16.
Anomalous high frequency PKKPBC signals (displaying a large amount of energy around 2.5 Hz), recorded globally for deep and intermediate depth earthquakes,
are compared to PKKPAB signals. The attenuation difference
t\textAB* - t\textBC* t_{\text{AB}}^{*} - t_{\text{BC}}^{*} is evaluated from spectral amplitudes in the range 96–111°, being approximately twice the results provided by full-wave theory
and PREM (with no low Qμ zone in the lowermost mantle and a nearly infinite QK in the outer core). Most ray paths for such recordings are piercing the D″ region in the proximity of regions where ultra-low
velocity zones (ULVZ) have been previously reported beneath the North Atlantic Ocean, the Southwest Pacific and the southwestern
part of South America. If BC amplitudes around 2.5 Hz and at low frequencies (0.5–1.5 Hz) are comparable, the observed attenuation
difference (in the frequency range 0.2–2.5 Hz) is small (around 0.25 s) and close to the PREM value. The particle motion of
the high-frequency PKKPBC at 2.5 Hz is quite similar to that of the raw recording, suggesting a deep source. An explanation for this might be scattering
of the BC branch in some very restricted areas of the lowermost mantle. Alternately, the presence of a thin layer with high
attenuation in the D″ region would most likely be associated with either the ultra-low velocity zone (ULVZ) or light sediments
on the underside of the core-mantle boundary (CMB). Correlated to other methods to investigate the lowermost mantle, the high-frequency
PKKPBC can be used to map lateral variations of attenuation above the CMB, possibly associated with the boundary of the superplumes,
especially when PKKPAB is observed. 相似文献
17.
We present a simple and efficient hybrid technique for simulating earthquake strong ground motion. This procedure is the combination
of the techniques of envelope function (Midorikawa
et al. Tectonophysics 218:287–295, 1993) and composite source model (Zeng
et al. Geophys Res Lett 21:725–728, 1994). The first step of the technique is based on the construction of the envelope function of the large earthquake by superposition
of envelope functions for smaller earthquakes. The smaller earthquakes (sub-events) of varying sizes are distributed randomly,
instead of uniform distribution of same size sub-events, on the fault plane. The accelerogram of large event is then obtained
by combining the envelope function with a band-limited white noise. The low-cut frequency of the band-limited white noise
is chosen to correspond to the corner frequency for the target earthquake magnitude and the high-cut to the Boore’s f
max or a desired frequency for the simulation. Below the low-cut frequency, the fall-off slope is 2 in accordance with the ω2 earthquake source model. The technique requires the parameters such as fault area, orientation of the fault, hypocenter,
size of the sub-events, stress drop, rupture velocity, duration, source–site distance and attenuation parameter. The fidelity
of the technique has been demonstrated by successful modeling of the 1991 Uttarkashi, Himalaya earthquake (Ms 7). The acceptable
locations of the sub-events on the fault plane have been determined using a genetic algorithm. The main characteristics of
the simulated accelerograms, comprised of the duration of strong ground shaking, peak ground acceleration and Fourier and
response spectra, are, in general, in good agreement with those observed at most of the sites. At some of the sites the simulated
accelerograms differ from observed ones by a factor of 2–3. The local site geology and topography may cause such a difference,
as these effects have not been considered in the present technique. The advantage of the technique lies in the fact that detailed
parameters such as velocity-Q structures and empirical Green’s functions are not required or the records of the actual time
history from the past earthquakes are not available. This method may find its application in preparing a wide range of scenarios
based on simulation. This provides information that is complementary to the information available in probabilistic hazard
maps. 相似文献
18.
The strong ground motions for the 2001 Bhuj (M
w 7.6) India earthquake have been estimated on hard rock and B/C boundary (NEHRP) levels using a recently modified version
of stochastic finite fault modeling based on dynamic corner frequency (Motazedian and Atkinson in Bull Seismol Soc Am 95, 995–1010 2005). Incorporation of dynamic corner frequency removes the limitations of earlier stochastic methods. Simulations were carried
out at 13 sites in Gujarat where structural response recorder (SRR) recordings are available. In addition, accelerograms were
simulated at the B/C boundary at a large number of points distributed on a grid. The corresponding response spectra have also
been estimated. The values of peak ground accelerations and spectral accelerations at three periods (0.4, 0.75 and 1.25 s)
are presented in the form of contour maps. The maximum value of peak ground acceleration (PGA) in the center of meizoseismal
zone is 550 cm/s2. The response spectral acceleration in same zone is 900 cm/s2 (T = 0.4 s), 600 cm/s2 (T = 0.75 s) and 300 cm/s2 (T = 1.25 s). The innermost PGA contour is on the fault plane. A comparison of the PGA values obtained at 13 sites in this study
with those obtained in earlier studies on the same sites, but employing different methods, show that the present PGA values
are comparable at most of the sites. The rate of decay of PGA values is fast at short distances as compared to that at longer
distances. The PGA values obtained here put some constraints on the expected values from a similar earthquake in the region.
A synthetic intensity map has been prepared from the estimated values of PGA using an empirical relation. A comparison with
the reported intensity map of the earthquake shows the synthetic MMI values, as expected, are lower by 1 unit compared to
reported intensity map. The contour map of PGA along with the contour maps of spectral acceleration at various periods permit
the assessment of damage potential to various categories of houses and other structures. Such information will be quite important
in planning of mitigation and disaster management programs in the region. 相似文献
19.
Microseismic noise was studied in the frequency range 0.5–30 Hz in the conditions prevailing in the town of Vorkuta. A seismic
noise model was developed consisting of power spectral densities of ground motion velocity separately for daytime and nighttime
in different frequency ranges. The absolute noise level for frequencies of 1–5 Hz in Vorkuta varies between −140 and −150
dB in daytime and from −152 to −158 dB in nighttime, with the ranges for the 8-15 Hz noise being −140 to −155 dB in daytime
and −155 to −165 dB in nighttime. Well-pronounced daily variations in noise amplitude were observed in the frequency ranges
1.5–3 Hz and 14–17 Hz. The noise amplitude varies by 7 dB over 24 hours, with the amplitude of horizontal component variation
being 5 dB above that of the vertical component. The power spectral densities of ground motion velocity in the microseismic
noise involve several spectral peaks, whose central frequencies did not vary by more than 0.15 Hz during the entire period
of instrumental observation. The seismic background in the town of Vorkuta contains seismic events due to distant earthquakes
and local industrial explosions. 相似文献
20.
Ground-motion prediction equations (GMPEs) for inelastic response and structural behaviour factors 总被引:1,自引:1,他引:0
The objective of this paper is to present ground-motion prediction equations describing constant-ductility inelastic spectral
ordinates and structural behaviour factors. These equations are intended for application within the framework of Eurocode
8. Most of the strong-motion data used in the present work is obtained from the ISESD (Internet Site for European Strong-motion
Data) databank. Present analysis includes ground motion records from significant Icelandic earthquakes, which are augmented
by records obtained from continental Europe and the Middle East. In all cases the selected ground motion records are generated
during shallow earthquakes within a distance of 100 km from the recording station. The classification of site conditions in
the present work is based on the Eurocode 8 definition. 相似文献