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1.
Amplification of earthquake-induced seismic waves by soft superficial deposits often causes significant damages in the urban areas. In predicting this effect for large future earthquakes, the linear elastic response of soils is customarily assumed. To check this assumption, we have analyzed surface and downhole acceleration data from the SMART1 and SMART2 strong motion arrays in Taiwan, covering peak accelerations of up to 0·3 g. First, frequency-dependent amplification induced by the alluvial deposits at the SMART1 array was estimated using spectral ratio technique, where the records at rock site were taken as a reference motion. Statistically validated reduction in soil amplification in the strong motion relative to the weak motion in the frequency range between approximately 1 and 9 Hz was detected. Secondly, relative site responses between the Pleistocene and recent sedimentary deposits at the SMART2 array were studied. Relative amplification was shown to be clearly dependent on the excitation level. Thirdly, we compared experimentally recorded uphole/downhole spectral ratios on weak and strong ground motion with the theoretical response yielded by the geotechnical code DESRA2 which assumes hysteretic constitutive relationship of soil. Major symptoms of nonlinear ground behavior predicted by the model were found in the observed data. Back-calculation of the shear wave velocities to the depth of 47 m shows nearly 50% decrease in the strongest quakes, also accounted for by the nonlinear soil behavior. 相似文献
2.
地震反应分析中输入界面选取合理与否对设计地震动参数有重要影响。基于唐山地区钻孔剖面,分别选取剪切波速为500m/s的硬黏土和800m/s的岩石顶面作为基岩输入界面,采用一维等效线性化方法讨论中硬场地输入界面的选取对地表地震动参数的影响,结果表明:(1)地表峰值加速度放大倍数及地表加速度反应谱特征周期都随输入界面深度的增加而递增,且这种递增与输入地震动的强度及频谱特性都有密切联系;(2)随着输入界面深度的增加,地表加速度反应谱几乎全频段内增大,仅在短周期内出现减小的情况,但幅度十分有限;(3)中硬场地地震反应分析中基岩输入界面宜取剪切波速为800m/s的土层顶面。 相似文献
3.
通过对2001年昆仑山口西8．1级地震区冻土震害考察研究表明，震区主要存在冰碛、冲积、洪积和湖积等成因的冻土，沿地震破裂带冻土厚度变化较大。震区冻土变形破坏主要包括地震构造成因的地震破裂带和由地震振动引起的裂缝、液化、震陷和崩塌等。冻土中地震破裂带在地表主要以脆性变形为主，在地震断裂左旋走滑运动作用下，主要由剪切裂缝、张裂缝和开裂的挤压鼓包等组成。裂缝、液化、震陷和崩塌等变形破坏的展布特征及其组合形式与震区岩土与环境条件密切相关；本次地震震害具有地震破裂带规模大、有建筑物分布的青藏公路一线地震烈度衰减较快和震害分布受岩土条件影响大等特点。 相似文献
4.
5.
本文选取山东地区2个Ⅲ类场地的工程地质勘探及土层剪切波速等资料,将土层厚度按5个深度段,每个分段给出了4个土层剪切波速的改变量,通过改变不同深度段土层剪切波速,建立了19种土层地震反应分析模型,分析了不同深度段,不同概率水平下土层剪切波速的变化对场地地震动参数的影响。研究表明,不同深度段土层剪切波速的变化对场地地震动参数的影响有差异。具体表现为,土层剪切波速的改变在1—10m、11—40m和地震输入界面处三个深度段对地震动加速度峰值影响较大;其中,41—70m和71—100m两个深度段剪切波速的改变对地震动加速度峰值影响小;在土层深度1—10m时,剪切波速降低,峰值变大,剪切波速的改变与峰值的改变呈负相关;在其它深度段,剪切波速降低,峰值变小,剪切波速的改变与峰值的改变呈正相关。剪切波速的改变在1—10m和11—40m两个深度段对地震加速度反应谱影响较大;在41—70m、71—100m和地震输入界面三个深度段对地震加速度反应谱影响很小。 相似文献
6.
2020年7月12日发生了唐山古冶5.1级地震,其强震动影响波及京津唐地区,特别是北京城区也出现了强烈的震感。中国强震动观测台网、国家地震烈度速报台网及典型建筑结构地震反应观测台阵获得大量的强震动记录。这次地震震级不大,但为地震科学研究提供了较为丰富的信息。基于获得的地震影响信息,可开展以下方面的研究:①利用地震附近及区域范围内地震烈度速报台网的密集观测记录,开展地震影响烈度快速计算分析及台网功能可靠性检测;②利用北京和天津地区的强震动观测记录,探讨深厚覆盖土层和盆地场地地震动影响;③利用京津唐地区震中距至300 km的强震动观测记录,研究京津唐地区的地震动衰减特性;④利用北京城区的建筑结构地震反应观测台阵记录,分析典型工程结构地震反应特征;⑤其他,如场地土层参数和工程结构参数反演研究等。本文针对以上关注的问题,介绍了相关初步研究工作并开展了进一步探讨性分析研究,展示了唐山古冶5.1级地震影响的丰富信息和对相关研究的潜在推进作用。 相似文献
7.
Centrifuge modeling of seismic response of layered soft clay 总被引：1，自引：0，他引：1
Centrifuge modeling is a valuable tool used to study the response of geotechnical structures to infrequent or extreme events
such as earthquakes. A series of centrifuge model tests was conducted at 80g using an electro-hydraulic earthquake simulator mounted on the C-CORE geotechnical centrifuge to study the dynamic response
of soft soils and seismic soil–structure interaction (SSI). The acceleration records at different locations within the soil
bed and at its surface along with the settlement records at the surface were used to analyze the soft soil seismic response.
In addition, the records of acceleration at the surface of a foundation model partially embedded in the soil were used to
investigate the seismic SSI. Centrifuge data was used to evaluate the variation of shear modulus and damping ratio with shear
strain amplitude and confining pressure, and to assess their effects on site response. Site response analysis using the measured
shear wave velocity, estimated modulus reduction and damping ratio as input parameters produced good agreement with the measured
site response. A spectral analysis of the results showed that the stiffness of the soil deposits had a significant effect
on the characteristics of the input motions and the overall behavior of the structure. The peak surface acceleration measured
in the centrifuge was significantly amplified, especially for low amplitude base acceleration. The amplification of the earthquake
shaking as well as the frequency of the response spectra decreased with increasing earthquake intensity. The results clearly
demonstrate that the layering system has to be considered, and not just the average shear wave velocity, when evaluating the
local site effects. 相似文献
8.
Conventionally, evaluation of liquefaction potential of loose saturated cohesionless deposits as specified in Japanese design codes employs peak ground acceleration (PGA). However, recent large-scale earthquakes in Japan revealed that liquefaction at some sites did not occur even though large PGAs were recorded at or near these sites. As an alternative approach, an evaluation procedure based on peak ground motion parameters, i.e. incorporating both PGA and the peak ground velocity (PGV), is proposed. By performing parametric studies using one-dimensional seismic response analysis and formulating regression models, seismic-induced shear stresses within the deposit are expressed in terms of peak ground motion parameters at the surface, and these are used to calculate the factor of safety against liquefaction. Application to case histories in Japan indicates that the proposed two-parameter equation can adequately account for the occurrence and non-occurrence of liquefaction at various sites as compared to the conventional PGA-based approach. Moreover, analyses of several strong motion records at various sites show that liquefaction may occur when PGA≥150 gal and PGV≥20 kine, indicating that these values can serve as thresholds in assessing the possible occurrence of liquefaction. 相似文献
9.
During the recent earthquakes in Japan and the U.S.A. a number of records from liquefied‐soil sites have been obtained. The ground motion parameters from these sites were studied and several methods for detection of liquefaction from seismic records were developed. The methods, however, focus mainly on the horizontal ground motion and may interpret as liquefaction‐induced some records from soft‐soil deposits or records with dominant surface waves, at which sites the phenomenon was not observed. Besides, not all of the available records from liquefied sites were processed. In this paper, after examination of the ability of different types of ground motion parameters to indicate alone soil liquefaction we propose a new liquefaction detection method that simultaneously analyses instantaneous frequency content of the horizontal and the vertical ground acceleration. We also compare performance of the proposed method with that of the other liquefaction detection methods. The computations are carried out using a common data set including records from liquefied and non‐liquefied sites. Results show that the frequency‐related parameters and the proposed method detect more efficiently the occurrence of liquefaction from the seismic records. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
10.
以Ⅱ类场地为例,选取了山东地区2个场地的工程地质勘探及剪切波速等资料,通过改变不同深度段波速,分别建立土层模型,计算分析了不同深度段、不同概率水平条件下剪切波速的变化对场地地震动参数的影响。研究结果表明,剪切波速的变化对场地地震动加速度峰值影响在浅层影响最大,基岩输入面处次之,深层最小;对特征周期的影响,在浅层影响最大,深层次之、基岩输入面处最小。研究结果为进一步研究土层剪切波速测试中的不确定性对场地地震动参数的影响及合理确定场地地震动参数提供一定的参考。 相似文献
11.
《地震工程与工程振动(英文版)》2015,(1)
Prediction of peak ground acceleration is an essential element in engineering seismology and it has received great attention in last few decades. In this paper, a comprehensive database of the strong-motion records of the 2008 great Wenchuan Ms 8.0 earthquake is analyzed to investigate the seismic attenuation relationship and the directivity effects. In contrast to most existing seismic attenuation models, the proposed model considers explicitly the directivity effect which has primary infl uence on the magnitude of ground motion. Bayesian model updating is used to obtain the model parameters and the associated uncertainty. Comparative study is performed with the well-known Boore-Joyner-Fumal empirical formula. Results show that consideration of the directivity effect is vital in modeling the seismic attenuation relationship. 相似文献
12.
建立合理的地震烈度与地震动参数之间的对应关系,在工程抗震及烈度速报中有着十分重要的作用,文中以美国加州3次破坏性地震和我国今年来6次地震中所获得的强震记录作为数据源,应用最小二乘法进行线性回归,得到了不同地震动参数与烈度间的相关性.经统计发现,在地面加速度峰值、标准累计绝对速度等12种描述地震动强度的参数中,各种参数在... 相似文献
13.
软土具有高灵敏度、低强度等特性,在地震过程中极易产生震陷。基于OpenSees数值模拟方法对软土场地的震陷反应进行非线性动力有限元分析,通过改变地震动峰值加速度、频谱特性、输入方式来研究其对软土震陷的影响。结果表明,地震动峰值加速度对地基土的不均匀震陷有显著影响,地震动峰值加速度越大,震陷量显著增大,震陷影响深度更大,对水平地表造成的破坏范围也更大;地震动频谱特性对软土震陷有重要影响,当地震动卓越频率与场地自振频率相近时,其幅值越大,产生的震陷越严重;水平、竖向同时输入地震动的方式能更好地反映土体的振动及震陷响应。该研究成果对探索软土震陷的机理有一定的指导意义。 相似文献
14.
Jiang Jinren Lu Qinnian and Sun JingjiangInstitute of Engineering Mechanics SSB Harbin ChinaHarbin University of Architecture Engineering Harbin China 《中国地震研究》1995,(4)
The statistical characteristics of strong ground motion specified by response spectrum and power spectral density function are studied using 190 strong-motion records of the Haicheng and Tangshan earthquakes in China and 138 earthquakes in the western United States.The response spectrum is normalized by the peak ground acceleration(i.e.,represented as spectral magnification factor),and the power spectral density function is described by the Kanai-Tajimi spectrum.The statistics and dependence of parameters are evaluated,and correlations between the spectral magnification factor or Kanai-Tajimi spectral parameters and the site condition,epicentral distance,or local magnitude are investigated.The statistical characteristics of spectra China and the U.S.A.are compared.Based on the results obtained the values of the statistics on spectral parameters for earthquake engineering applications in China are suggested. 相似文献
15.
以天津滨海某软弱场地为例,在不同强度不同相位的地震动时程输入下,用等效线性化技术考虑土的动力非线性特性,计算水平成层场地的地震反应,研究天津地区厚层淤泥质粉质黏土的动剪模量比和阻尼比与剪应变幅值的关系曲线的变异性对深软场地地表峰值加速度及其反应谱的影响。结果表明:(1)在阻尼比较均值加减一倍标准差对地表地震动参数变化影响不大;(2)在动剪模量比均值增加或减1倍标准差,对2%超越概率水平下地表峰值加速度影响显著,对应地表峰值加速度可能增加或减小20%~30%,其地表反应谱谱型也有变高变瘦或变矮变胖的趋势;(3)在动剪切模量均值减1倍标准差时,对10%超越概率水平下的地表峰值加速度的影响比较显著,减小幅度在15%左右,反应谱也存在变矮变胖的趋势;在动剪切模量均值加1倍标准差时,对10%超越概率水平下的地表地震动参数影响不明显;(4)在动剪切模量或阻尼比均值加减1倍标准差时,对63%的地表地震动参数影响均不明显。 相似文献
16.
Near-field horizontal and vertical earthquake ground motions 总被引：8，自引：0，他引：8
Strong-motion attenuation relationships are presented for peak ground acceleration, spectral acceleration, energy density, maximum absolute input energy for horizontal and vertical directions and for the ratio of vertical to horizontal of these ground motion parameters. These equations were derived using a worldwide dataset of 186 strong-motion records recorded with 15 km of the surface projection of earthquakes between Ms=5.8 and 7.8. The effect of local site conditions and focal mechanism is included in some of these equations. 相似文献
17.
以反应谱和功率谱密度函数表征的强震运动的统计特性 总被引：1，自引：0，他引：1
文中利用我国海城和唐山地震１９０条强震记录和美国西部１３８条强震记录研究了以反应谱和功率谱密度函数表征的强震运动的统计特性。反应谱用最大地面加速度归一化，即表为谱放大系数，功率谱密度函数用金井清谱描述。文中研究了参数的统计值和依赖性，以及谱放大系数和金井清谱参数与场地条件、震源和震中距等之间的相关性，分析比较了中美两国强震运动谱的统计特性，并对我国地震工程应用的强震运动谱的统计参数值的选取提出了建议。 相似文献
18.
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
19.
Housner谱烈度及修正谱烈度作为基于加速度记录时程直接得到的地震动强度参数,与建筑结构破坏及地震宏观烈度存在较高的相关性,是可靠的地震仪器烈度物理参数指标。然而,相对于地面加速度峰值、地面速度峰值等地震动峰值参数,三分量加速度记录对应的谱烈度计算过程较为复杂,耗时相对较长,影响了利用谱烈度确定地震仪器烈度的时效性。基于对强震动加速度记录的统计分析,本文提出了谱烈度的快速近似算法,仅计算4个方向上的谱烈度值,采用其中3点作圆即可获得水平面内谱烈度迹线的近似最大值,使计算速度提高了45倍,且保持了谱烈度作为地震仪器烈度物理指标的精度。利用在汶川MS 8.0地震等386次MS > 3.0地震中获取的2701组强震动加速度记录,经可靠性检验,结果表明所提出的Housner谱烈度快速近似算法的计算误差在±4.5%以内,可以同时满足地震仪器烈度速报的可靠性和时效性需求。 相似文献
20.
强震仪和测震仪均能记录地面运动,强震仪输出的加速度记录主要用于分析结构地震反应,测震仪输出的速度记录常用于确定地震信息.由于这2种记录均描述地面运动,且覆盖结构地震反应分析所需频带范围,速度记录能否用于计算结构地震反应引起了人们的关注.为分析开源Hi-net速度记录用于计算结构地震反应时的精度,作者选取同台记录的加速度... 相似文献