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1.
V. S. Phanikanth Deepankar Choudhury G. Rami Reddy 《Geotechnical and Geological Engineering》2011,29(6):1109-1126
Any earthquake event is associated with a rupture mechanism at the source, propagation of seismic waves through underlying
rock and finally these waves travel through the soil layers to the particular site of interest. The bedrock motion is significantly
modified at the ground surface due to the presence of local soil layers above the bedrock beneath the site of interest. The
estimation of the amplifications in ground response due to the local soil sites is a complex problem to the designers and
the problem is more important for mega cities like Mumbai in India, where huge population may get affected due to devastations
of earthquake. In the present study, the effect of local soil sites in modifying ground response is studied by performing
one dimensional equivalent-linear ground response analysis for some of the typical Mumbai soil sites. Field borelog data of
some typical sites in Mumbai city viz. Mangalwadi site, Walkeswar site, BJ Marg near Pandhari Chawl site are considered in
this study. The ground responses are observed for range of input motions and the results are presented in terms of surface
acceleration time history, ratio of shear stress to vertical effective stress versus time, acceleration response spectrum,
Fourier amplitude ratio versus frequency etc. The typical amplifications of ground accelerations considering four strong ground
motions with wide variation of low to high MHA, frequency contents and durations are obtained. Results show that MHA, bracketed
duration, frequency content have significant effects on the amplification of seismic accelerations for typical 2001 Bhuj motion.
The peak ground acceleration amplification factors are found to be about 2.50 for Mangalwadi site, 2.60 for Walkeswar site
and 3.45 for BJ Marg site using 2001 Bhuj input motion. The response spectrum along various soil layers are obtained which
will be useful for designers for earthquake resistant design of geotechnical structures in Mumbai for similar sites in the
absence of site specific data. 相似文献
2.
S. A. Agafonova N. L. Frolova I. N. Krylenko A. A. Sazonov P. P. Golovlyov 《Natural Hazards》2017,85(1):171-195
The site amplification functions at 48 sites of NCR have been estimated in this study using the waveforms of locally recorded 23 earthquakes. Due to the absence of a suitable reference site in the region, the widely used horizontal-to-vertical spectral ratio (HVSR) technique has been used for this purpose. The maps showing the spatial distribution of predominant frequencies and the site amplifications at different frequencies corresponding to the natural frequencies of the different-storey buildings have been presented. The predominant frequencies in general are found to be in the range 2.5–7.5 Hz with an average of 4.4 Hz for the region having older alluvium sediments and in the range 1.1–6.4 Hz with an average of 3.3 Hz for the region with the younger alluvium deposits. The average value of the site amplifications for the frequency band 3.0–10.0 Hz is in the range 2.0–5.3 for the sites with significant soil cover, while the spectral amplification corresponding to the predominant frequency varies from 2.5 to 7.5 at most of the sites. The spectral amplification level lies in the range 2.0–3.0 for the sites with less or no sediment cover. The spectral amplification levels presented for the different-storey buildings may be used for the mitigation of seismic hazard in the region. The estimated site amplification functions may be used in the simulation of the site-specific strong ground motions and therefore useful for the evaluation of seismic hazard of a region. 相似文献
3.
Site response studies in Agartala Urban agglomeration 总被引：1，自引：0，他引：1
A systematic investigation using digital microearthquake recorders with short period SS-1 seismometers, covering 76 sites
in and around Agartala city, has been carried out for site response (SR) studies in the area. In the northern part of the
area, SR varies from 1.15 to 1.85 corresponding to peak frequency 0.76 to 0.93 Hz where soil is mostly semi-consolidated and
stiffer than recent Quaternary deposits (Haora River formation). In the southern part of the area, SR varies from 1.12 to
2.42 corresponding to peak frequency from 0.71 to 0.85 Hz within the Dupitila formation (early Quaternary). It is observed
that estimated SR from H/V increases from edges to middle of the Haora River valley and impedance contrast fallows the similar
trend. This reflects that site response by H/V is influenced by impedance contrast, whereas computed amplification from 1-D
model shows opposite trend. The maximum amplification at fundamental frequency of resonance, 1.04 Hz estimated from H/V by
near to BH-7, is 2.5 times greater than the impedance contrast/ratio derived from 1-D model for same location. Relationship
between resonance frequency and depth was obtained by applying quarter wavelength and Bard (2000) methodologies, which shows linearity, whereas H/V shows its nonlinearity characteristic in soil across the valley part of
Haora River. Shear wave velocities, and subsequently, SPT index and factor of safety (by cyclic stress approach) were estimated
from geotechnical parameters. Vs30 and site response data were used in this study for getting a first hand information about
soil stiffness condition in the area. The estimation of SPT index and factor of safety could be a useful tool for delineating
liquefied and none liquefied zones at various depth levels, especially where water table exists at a very shallow level. The
expected liquefiable zone was observed at depths varying from 6–25 m beneath the soil bearing zones where percentage of fines
is estimated to be more than 35% for the area. This knowledge about subsurface soil characteristics will be useful for the
civil engineers/city planners, which can be taken into account at the time of constructing earthquake-resistant structures
in the area. 相似文献
4.
Avcılar is the suburb of Istanbul that was most heavily damaged during the August 17, 1999 Mw 7.4 Izmit earthquake. Strong ground motion caused fatalities and damage in Avcılar despite being 90 km from the epicenter. We deployed five portable seismograph stations equipped with Reftek 24-bit recorders and L4C-3D seismometers for 2 months, in order to understand why the local site response was different from elsewhere in Istanbul. A reference station was placed on a hard rock site, and the remaining four stations were placed on other geological units, in areas that had experienced varying levels of damage. We calculated frequency-dependent ground amplification curves by taking the ratios of the spectra at soft and hard rock sites. We obtained similar site response curves for most earthquakes at each site in the frequency range of 0.3–1.6 Hz, and observed no significant site amplification beyond 2.0 Hz at any site. The overall characteristics of the recorded S-waveforms and our modeling of the calculated site amplification curves are consistent with amplification as a result of trapping of seismic energy within a 100–150 m thick, low-velocity subsurface layer. We also review the applicability of microtremor measurements to estimate local site effects at Avcılar. For these data, we used ratios of spectra of horizontal to vertical components to obtain each site response. These results are compared with standard spectral ratios. These microtremor measurements provide consistent estimates of the amplification at most sites at the higher end of the frequency band, namely above 1 Hz. The results from both methods indeed agree well in this part of the frequency band. However, the microtremor method fails to detect amplification at lower frequencies, namely <1.0 Hz. 相似文献
5.
S. K. Nath P. Sengupta S. K. Srivastav S. N. Bhattacharya R. S. Dattatrayam R. Prakash H. V. Gupta 《Journal of Earth System Science》2003,112(3):441-462
Site response in and around Delhi is studied using digital seismograms recorded by a thirteen-station VSAT-based 24-bit digital
Delhi telemetry network of the India Meteorological Department. Nine local (M
l ≥ 2.3) and nine regional (M
l ≥ 3.9) earthquakes are selected for the estimation of site amplification factor using the classical standard spectral ratio
for regional events (Ridge Delhi Observatory being the reference station), normalized standard spectral ratio for local events,
horizontal-to-vertical spectral ratio or receiver function and the generalized inversion techniques in the frequency range
of 0.5 to 7.5 Hz. Site response curves at all the thirteen stations exhibit station to station variation of the site amplification
factor reflecting the changes in geologic/geotectonic/soil conditions. A comparison of the site response values obtained by
the generalized inversion with those computed using receiver function technique shows a large scatter even though the pattern
of the curves remain more or less similar. However, the site effects computed by generalized inversion and standard spectral
ratio exhibit a good 1:1 correspondence. The peaks yielded by all the methods have been observed to occur at the same frequencies.
It is evident that the softer fluvial deposits of the newer alluvium of the east Yamuna sector show steeper site amplification
gradient at lower frequencies, while the greater Delhi experiences moderate site amplification. The variation of site response
corroborates the abrupt changes in intensity from one location to another due to local site condition. 相似文献
6.
Soil liquefaction studies at Mumbai city 总被引：1，自引：0，他引：1
Mumbai city is the economical capital of India and is situated about midway on the western coast of stable continental region of Peninsular India. Major part of the city being of reclaimed land, the soil type is of alluvium, sand, and recent conglomerate. There are some bigger water bodies within the city range. In this study, an attempt has been made to study the susceptibility of soil liquefaction using simplified empirical procedure based on number of blow counts (N values) of the soil layers from standard penetration test. The liquefaction susceptibility is quantified in terms of factor of safety along the borehole depths at available borehole locations using earthquake-induced cyclic stress on the soil and the cyclic resistance of the soil to withstand the load. The factor of safety against liquefaction is evaluated at different sites for two peak ground acceleration (PGA) levels pertaining to 10 and 2?% probability of exceedance in 50?years corresponding to uniform hazard response spectra for Mumbai city with 475- and 2,475-year return period, respectively. Contour maps are prepared that display the factor of safety at different depths for earthquake magnitude of M w 6.5. These contour maps show the liquefaction vulnerability at different sites in the city. 相似文献
7.
Recent destructive earthquakes have clearly shown that near-surface geological conditions play a major role in the level of
ground shaking in urban areas. In Canada, Montreal is ranked second for seismic risk after Vancouver considering its population
and regional seismic hazard. The city is largely built on recent unconsolidated marine and river deposits and most of its
infrastructure is old and deteriorated. A seismic risk project that includes a combined methodology for site effects zoning
in large cities, using microtremor measurements (H/V method) coupled with 1D numerical modelling (SHAKE91), has been initiated. The experimental approach gives good estimates
of the fundamental frequency of soft deposits, while the numerical approach provides good estimates of the soil response in
terms of amplification factor related to frequency. Main mechanical properties of soft soils were compiled from various data
available, and a sample of input rock motions from real and synthetic earthquakes was used to compute soil response. The influence
of marine clays on soil response is significant and is well correlated with thickness of these deposits. PGA amplification
factors range from 2 to 4 at frequencies from 2 to 7 Hz, with some occasional larger values. The results demonstrate that
the methodology used for our study is both fast and efficient to determine the influence of soft soils in urban environments.
Such studies are essential for the effective deployment of seismic instrumentation, land-use planning and seismic mitigation. 相似文献
8.
针对基岩明显起伏、土层非均匀分布的典型河口盆地场地,考虑土体非线性特征,采用黏弹性人工边界模拟无限域对地震波动的影响,建立大尺度精细化二维有限元模型,分析了盆地地表地震动幅值、频谱、持时、传递函数特征,探讨了基岩起伏土层的地震动聚集效应及盆地边缘效应。结果表明：（1）盆地近地表土层表现出不同程度的地震动放大效应,且随土层深度增加呈非单调递减特征,基岩突变处地震动聚集效应明显,盆地两侧产生较为显著的边缘效应;场地中、长周期地震动的放大作用显著;（2）多遇地震、偶遇地震和罕遇地震水平时,场地卓越周期依次介于0.35～0.65 s、0.40～0.75 s和0.50～1.05 s之间;给出了盆地地表PGA（地表峰值加速度）、卓越周期均值等值线图及地表加速度反应谱放大因子建议值,地表设计地震动参数amax（地震影响系数）与Tg（特征周期）明显大于现行《建筑抗震设计规范》取值;（3）盆地特殊位置地表地震动持时得到不同幅度增长,且与输入地震动特性相关;（4）该盆地对0.5～2.0 Hz频段基岩地震动的放大效应比较显著,对小于0.2 Hz或大于2.5 Hz的基岩地震动,该盆地地震动放大效应不明显;（5）福州城区及其邻近区域地震动放大效应普遍较大。大尺度二维非线性分析一定程度上能合理反映微地形起伏、土层分布及土体非线性对地震波传播过程的影响。 相似文献
9.
Sumer Chopra Dinesh Kumar B. K. Rastogi Pallabee Choudhury R. B. S. Yadav 《Natural Hazards》2013,65(2):1135-1155
Site response in the Gujarat region is studied using local earthquake data recorded at 32 sites spread all over Gujarat region, India. Out of these 32 sites, 15 sites are located in Kachchh region, 8 in Saurashtra and 9 in mainland Gujarat region. These sites are underlain by different types of rocks/sediments of different ages. Out of 32 stations, 7 stations are on Quaternary deposits, 6 on Tertiary, 11 on Deccan, 3 on Jurassic, 3 on Cretaceous and 2 on Proterozoic rocks. The predominant frequencies at these sites depend strongly on the local geology. The average predominant frequencies of the sites on Quaternary sediments are 2.4?Hz, 5.3?Hz on Tertiary, 7.5?Hz on Jurassic, 7.2?Hz on Deccan, 4.6?Hz on Cretaceous and 7.5?Hz on Proterozoic formations. The average site amplification values at predominant frequencies are 3.7 for the sites of Quaternary deposits, 3.3 for Tertiary, 3.3 for Cretaceous rock, 4.2 for Deccan trap, 4.1 for Jurassic sites and 4.6 for Proterozoic. The damage to the houses during 2001 Bhuj earthquake is compared with the amplification at predominant frequencies at those sites. The spatial variation of predominant frequencies and the site amplifications at different frequencies corresponding to the natural frequencies of different storey buildings are studied, which will be useful in the evaluation of seismic hazard in the region. 相似文献
10.
The seismic events recorded at two accelerographs installed at Sellano (central Italy) during the 1997–1998 Umbria seismic sequence, one on detritic material, at the historical centre, and the other one on rock, about 200 m distant, were analysed in terms of spectral amplification of the historical centre site. Epicentres were mainly concentrated in the north and south-east directions of Sellano area. The SH wave component average amplifications were evaluated from the smoothed Fourier spectral ratios of the recordings on soil and rock sites, along the two main epicentral lines. Similar amplifications resulted, with two main peaks in the frequency range of 3–5 Hz, corresponding to the eigenfrequencies of the damaged buildings. Shear velocities of the shallowest 30 m of soils were obtained by FTAN measurements along refraction seismic spreadings, and utilized to compute spectral amplification of soil station to rock station along the geological cross sections. A good agreement was found between observed Fourier spectral ratios and the computed 2D amplification modelling, which explains the damage level of the historical buildings beside the degraded conditions of brick masonry. 相似文献
11.
Sumer Chopra Dinesh Kumar B. K. Rastogi Pallabee Choudhury R. B. S. Yadav 《Natural Hazards》2012,60(2):517-540
In this study, the modified stochastic method based on dynamic corner frequency has been used for the simulation of strong
ground motions in Gujarat region. The earthquake-generating faults have been identified in the Gujarat region on the basis
of past seismicity of the region. In all, 19 probable faults have been identified with 12 in Kachchh region, 5 in Saurashtra
and 2 in Mainland Gujarat region. The maximum magnitude has been assigned to each fault based on the regional tectonic environment
and past seismicity. The strong ground motions from these identified sources have been estimated at numerous points distributed
all over Gujarat region on a grid. The peak ground acceleration (PGA) values have been extracted from the accelerograms and
contoured. The spatial distribution of maximum of 19 PGA values at every grid point have been described and discussed. The
ground motions at the surface of 32 important cities of the Gujarat have been estimated by incorporating the site amplification
functions. The site amplification functions are obtained using the local earthquake data. These cities are located on various
types of geological formations. We note that the site amplification functions have modified the character of the records and
amplified the acceleration values at almost all the sites. The Kachchh region can expect surface accelerations between 400
and 800 cm/s2, Saurashtra between 100 and 200 cm/s2 and Mainland less than 50 cm/s2 from a future large earthquake. The obtained results are useful for disaster mitigation measures, strengthening the existing
built environment and design of structures in the region. 相似文献
12.
Davor Stanko Snježana Markušić Stjepan Strelec Mario Gazdek 《Environmental Earth Sciences》2017,76(18):642
This paper presents a major extension of seismic vulnerability research project on the site of Trako??an Castle based on the initial horizontal-to-vertical-spectral-ratio (HVSR) results from Stanko et al. (2016). The estimated HVSR site frequencies and HV amplification at Trako??an Castle can only be used as an indication of the initial soil site frequency and amplification, so-called natural soil model, corresponding to the subsoil profile without the influence of an earthquake. The equivalent-linear (EQL) site response analysis has been carried out for different earthquake scenarios for a maximum input rock peak ground acceleration (PGAROCK) that corresponds to return periods of 95 (0.08 g), 475 (0.18 g) and 1000 years (0.31 g). The aim of the research is to evaluate structural seismic design responses and to determine type and degree of damage caused by local site effect, which is the result of an alluvial basin and topographic influences. The main objective of this research is the formation of local microseismic zones based on an EQL analysis: surface spectral acceleration and amplification maps at the predominant frequency. Based on the HVSR frequency response of the core structure of Trako??an Castle and the Tower itself (fundamental and higher frequency modes), maps of surface spectral acceleration and soil amplification at different frequencies (3, 5 and 10 Hz) are developed for different input PGAROCK levels (0.08, 0.18 and 0.31 g) to evaluate seismic response of the Castle. Observed amplifications are correlated with ground motion polarization and directionality of the ground motion from the alluvial basin to the hilltop. Shortening of predominant frequencies (lengthening of the period), particularly in the alluvial basin, has been observed with higher input PGAROCK in the EQL analysis. This effect is not manifested in the Trako??an hill, and predominant frequencies match HVSR frequencies. The use of certain geophysical survey methods at historical sites is a big problem, because terrain features (e.g. steep hills, mountains, ridges, slopes, cliffs) create lack of space and make it impossible to carry out geophysical investigation. Microtremor measurements at historical sites can overcome this limitation and provide local seismic response and vulnerability behaviour of historical monuments without destroying their authenticity. Also, computational modelling can greatly improve the results. The EQL site response analysis on the site of Trako??an Castle has confirmed and improved the results of seismic response and vulnerability based on HVSR method. 相似文献
13.
A. K. Mundepi 《Journal of the Geological Society of India》2013,81(6):767-773
Fundamental frequency map of site amplification at different sites in Doon valley, Uttarakhand, India is prepared from microtremor (ground ambient noise) using Horizontal to Vertical Spectral Ratio (HVSR) technique. The fan deposited alluvium filled synclinal valley of Doon lies between Main Boundary Thrust (MFT) and Himalayan Frontal Thrust (HFT) in the Himalayan active seismic belt and experienced many earthquakes in the past. The HVSR at different sites in the Doon valley ranges between the predominant frequencies 0.13 and 12.77 Hz. The HVSR in lower frequencies indicates that the site has either thick sediment covers or less compact rocks with fractures. Based on information on fundamental frequency and soft soil thickness, site classification map is generated. Results indicate that degree of compactness of rock types and presences of sediments vary significantly, which may play a major role in seismic hazard. The use of microtremor, therefore, constitutes an effective and inexpensive approach to site response and soft soil thickness estimation for preliminary microzonation. 相似文献
14.
福建沿海地区地微动的谱结构特征 总被引：7，自引：0，他引：7
在福建沿海地区的福州、泉州、莆田等地进行了场地地微动的测试 ,利用快速富里叶变换 (FFT)方法对观测到的地微动信号进行频谱分析。结果表明 ,覆盖层厚度大、有厚层的软弱夹层淤泥的场地 ,其整体刚度小 ,地微动谱能量相当分散 ,频带宽 ,峰值频率低 ,卓越频率一般为 1～ 5Hz ;覆盖层薄、土层刚度 (Vs)大的场地 ,地微动的峰值频率也大 ,卓越频率一般为8～ 11Hz,且常呈单峰形态。软土对高频地微动信号有滤波作用 ,对低频信号起放大作用 ,而硬土层则相反. 相似文献
15.
Deterministic seismic microzonation of Kolkata city 总被引：1，自引：0，他引：1
This paper presents the deterministic seismic microzonation of densely populated Kolkata city situated on the world’s largest
delta island with very soft and thick soil deposit in the surficial layers. A fourth-order accurate staggered-grid finite-difference
algorithm for SH-wave propagation simulation in visco-elastic medium is used for the linear computation of ground motion amplifications
in sedimentary deposit. Different maps such as for fundamental frequency (F
0), peak ground acceleration (PGA), peak ground velocity, and peak ground displacement are developed for variety of end-users
communities, including structural and geotechnical engineers for performance-based designs, building officials, emergency
managers, land-use planners, private businesses, and the general public. The scenario of simulated amplification factors in
the different frequency bands revealed that the Kolkata city is very much prone to severe damage even during a moderate earthquake
and very selective damage may occur at some of the localities during local and distant earthquakes. The deterministically
predicted PGA at bedrock level is 0.0844 g and the maximum PGA predicted at the free surface is 0.6 g in Kolkata city due
to maximum credible earthquake (M
w = 5.4) associated with Eocene Hinge Zone at a depth of 36 km. The seismic microzonation of Kolkata city reveals that the
Nager Bazar and Nimtala areas are the safest regions with earthquake point of view. 相似文献
16.
The evaluation of seismic site response in the urban area of Catania was tackled by selecting test areas having peculiar lithological
and structural features, potentially favourable to large local amplifications of ground motion. The two selected areas are
located in the historical downtown and in the northern part of Catania where the presence of a fault is evident. Site response
was evaluated using spectral ratio technique taking the horizontal- to-vertical component ratio of ambient noise. Inferences
from microtremor measurements are compared with results from synthetic accelerograms and response spectra computed at all
drillings available for this area. Such method is particularly suitable in urban areas where the nature of the outcropping
geological units is masked by city growth and anthropic intervention on the surface geology. The microtremor H/V spectral
ratios evaluated at soft sites located within the downtown profile tend to be smaller than that usually reported in the literature
for such soils. A tendency for amplifications to peaks near 2 Hz is observed only in some sites located on recent alluvial
deposits. Evidences for amplifications of site effects (frequency range 4–8 Hz) were observed in the sampling sites located
on the fault, with a rapid decrease of spectral amplitude just a few tenths of metres away from the discontinuity. Numerical
simulations evidenced the importance of geolithological features at depth levels even greater than 20–30 m. Besides this,
the results strongly confirm the importance of the subsurface geological conditions, in the estimate of seismic hazard at
urban scale. 相似文献
17.
In this study, soil response was carried out for the Greater Delhi region. A folded Proterozoic formation was identified as Delhi ridge, passes through its central part along SSW–NNE direction, and appears to be a main geomorphic feature for the study area. The Delhi ridge is an exposed quartzite rock of about 10–100 m wide and ~25 km long with gentler dipping both toward east and west. We have considered the exposed part as an outcrop side near the ridge axis and the dipping area as rigid base away from the ridge axis for ground motion study during the occurrence of the 25 November 2007 earthquake with magnitude M L 4.3 (Richter scale) that occurred at Delhi–Haryana State boundary. The degree of shaking was very strong and reported major cracks in the buildings near the epicenter area. We have studied the soil response parameters at the surface level, considering horizontally stratified soil layers above rigid base. The equivalent linear method was used for soil response analysis at 25 sites in Greater Delhi area. The peak amplification factors vary from 3.2 to 5.9 and peak resonance frequency varies from 1.2 to 5.3 Hz. The correlation among the peak amplification factor (A) and frequency (f) was empirically established as A = 0.36f + 3.60. Increasing peak amplification factor was found at sites with increasingly thicker alluvium deposit with lower frequency contains ground motion and vice versa. Seismic zoning map was also reconstructed for peak amplification factors and predominant periods for the study area for the mitigation purposes of earthquake damage. The average shear wave velocity up to 30 m soil depth is also obtained for site classification. The average velocity to 30 m [ $ \overline{{V_{\text{s}} }} (30) $ ] is a widely used parameter for classifying sites for predicting their potentiality to amplify seismic shaking. A lower value [ $ \overline{{V_{\text{s}} }} (30) $ ] thus yields a more conservative estimate of ground motion, which generally increases as $ \overline{{V_{\text{s}} }} (30) $ decreases. Present estimate of $ \overline{{V_{\text{s}} }} (30) $ varies from 315 to 419 m/s. In this study, we have identified two site classes C and D, as per National Earthquake Hazard Reduction Program. The city planner or engineers can directly use these data for site-specific assessment during retrofitting of the existing structure, demolition of the old buildings and design a new structure to avoid major destruction of the buildings due to future earthquake. 相似文献
18.
The assessment of local site effects on seismic ground motions is of great importance in earthquake engineering practice.
Several destructive earthquakes in the past have demonstrated that the amplification of ground motion and associated damage
to structures due to local site conditions is a significant consideration in earthquake hazard analysis. A recent paper published
in this journal highlights the hazard posed by earthquakes in the megacity of Kolkata in India due to its seismic and geological
settings. The seismic hazard assessment study speculates that the deep alluvial deposit in the city may increase the seismic
hazard probably due to the amplification of the seismic energies. This paper focuses on the seismic response studies of the
various soil strata (i.e. for local subsurface conditions) obtained from various construction sites in the city for predicted
earthquake. It is very well recognized that site response studies (a part of seismic microhazard zonation for urban areas)
are the first step towards performance-based foundation design or seismic risk analysis and mitigation strategy. One of the
problems for carrying out site-specific study in Kolkata is the lack of recorded strong motion data in the city. Hence, this
paper outlines a methodology to carry out site-specific study, where no strong motion data or seismic data are available.
The methodology uses wavelet-based spectrum compatibility approach to generate synthetic earthquake motions and equivalent
linear method for seismic site response analysis. The Mega City of Kolkata has been considered to explain the methodology.
Seismic hazard zonation map by the Bureau of Indian Standards classifies the City of Kolkata as moderate seismic zone (Zone
III) with a zone factor 0.16. On the other hand, GSHAP(Global Seismic Hazard Assessment Program) map which is based on 10%
probability of exceedance in 50 years specifies a maximum peak ground acceleration (PGA) of 1.6 m/s2 (0.163 g) for this region. In the present study, the seismic response has been carried out based on GSHAP. The results of
the analysis indicate the amplification of ground motion in the range of 4.46–4.82 with the fundamental period ranging from
0.81 to 1.17 s. Furthermore, the maximum spectral accelerations vary in the range of 0.78–0.95 g. 相似文献
19.
A large part of the Sydney 2000 Olympic Site at Homebush Bay was reclaimed over several decades using an estimated 9 Mt of domestic, commercial and industrial waste. Past activities, such as reclamation of wetlands, land clearing, shoreline remodelling and industrial practices, have caused an adverse environmental impact on the Homebush Bay site. Core samples (n = 4513) collected from the reclaimed lands of Homebush Bay show that, prior to remediation, soil contaminated by heavy metals (Cr, Cu, Pb, Zn) may have posed a threat to groundwater in the area. Mean Pb concentrations from the three land types at the Olympic site range from 65 to 374 μg/g in reclaimed areas, 78–167 μg/g in landfill areas and 44–52 μg/g in non‐infilled areas, respectively. Heavy‐metal concentrations in soils from non‐infilled areas indicate that these parts of the site were uncontaminated. The distribution of heavy metals in soil samples revealed a close association between elevated concentrations and the presence of fill materials at the site. Metal concentrations were frequently above Australian and New Zealand Guidelines for Fresh and Marine Water Quality. The Olympic Coordination Authority's remediation strategy to clean up the Homebush Bay site included consolidating contaminated waste into landscaped hills, which were capped with impermeable clay and thermal destruction of scheduled waste on site. The primary aims of the current study were to provide a scientific foundation for the remediation/rehabilitation of natural systems, and to make a contribution to the Olympic Coordination Authority's Development Plan and Environmental Management System for the site. 相似文献
20.
Economic importance of major ports is well known, and if ports are located in seismically active regions, then site-specific
seismic hazard studies are essential to mitigate the seismic risk of the ports. Seismic design of port sites and related structures
can be accomplished in three steps that include assessment of regional seismicity, geotechnical hazards, and soil structure
interaction analysis. In the present study, site-specific probabilistic seismic hazard analysis is performed to identify the
seismic hazard associated with four typical port sites of Gujarat state (bounded by 20°–25.5°N and 68°–75°E) of India viz.
Kandla, Mundra, Hazira, and Dahej ports. The primary aim of the study is to develop consistent seismic ground motion for the
structures within the four port sites for different three levels of ground shaking, i.e., operating level earthquake (72 years
return period), contingency level earthquake (CLE) (475 year return period), and maximum considered earthquake (2,475 year
return period). The geotechnical characterization for each port site is carried out using available geotechnical data. Shear
wave velocities of the soil profile are estimated from SPT blow counts using various empirical formulae. Seismicity of the
Gujarat region is modeled through delineating the 40 fault sources based on the seismotectonic setting. The Gujarat state
is divided into three regions, i.e., Kachchh, Saurashtra, and Mainland Gujarat, and regional recurrence relations are assigned
in the form of Gutenberg-Richter parameters in order to calculate seismic hazard associated with each port site. The horizontal
component of ground acceleration for three levels of ground shaking is estimated by using different ground motion attenuation
relations (GMAR) including one country-specific GMAR for Peninsular India. Uncertainty in seismic hazard computations is handled
by using logic tree approach to develop uniform hazard spectra for 5% damping which are consistent with the specified three
levels of ground shaking. Using recorded acceleration time history of Bhuj 2001 earthquake as the input time motion, synthetic
time histories are generated to match the developed designed response spectra to study site-specific responses of port sites
during different levels of ground shaking. It is observed that the Mundra and Kandla port sites are most vulnerable sites
for seismic hazard as estimated CLE ground motion is in order of 0.79 and 0.48 g for Mundra and Kandla port sites, respectively.
Hazira and Dahej port sites have comparatively less hazard with estimated CLE ground motion of 0.17 and 0.11 g, respectively.
The ground amplification factor is observed at all sites which ranges from 1.3 to 2.0 for the frequency range of 1.0–2.7 Hz.
The obtained spectral accelerations for the three levels of ground motions and obtained transfer functions for each port sites
are compared with provisions made in Indian seismic code IS:1893-Part 1 (2002). The outcome of present study is recommended for further performance-based design to evaluate the seismic response of the
port structures with respect to various performance levels. 相似文献