云南测震台网台站场地响应与ML震级测定的讨论

利用2016年云南测震台网记录到的地脉动数据,运用H/V谱比法计算分析了47个测震台站在0.1～20.0Hz频段内的场地响应。选取2012～2016年期间云南测震台网记录到的ML≥2.5地震做单台震级偏差统计分析,挑出受场地放大作用而出现单台震级大于台网平均震级的台站做去场地放大校正,然后重新统计单台震级偏差情况。计算结果显示云南测震台网的台站受台基条件和所处位置等地质构造因素影响,均存在一定程度的场地放大作用,大部分台站场地响应的卓越频率为1～6Hz,放大倍数为2～4倍。受场地放大作用的影响,大姚、芒市等19个台站的单台ML震级大于台网平均震级。在去除场地放大作用后,台站单台震级与台网平均震级的偏差有所减小。     

利用不同方法估算流动台站的场地响应

本文以2003年7月21日云南大姚6.2级地震序列为例, 分别利用地面运动反演法(Moya方法)、 水平与垂直向之比法(Nakamura方法)和参考台站法研究大姚地区场地响应特征。主要结论有: ① Moya方法计算的场地响应结果表明, 大姚地区场地的放大作用是比较明显的, 平均在3~20倍, 最高达到40倍; 卓越频率位于3~6 Hz之间, 但在高频处(约10 Hz以上)场地响应衰减得比较明显; 不同岩性台基的台站, 其场地响应结果存在一定的差别, 台基为风化砾岩的场地响应结果比较平缓, 其场地响应值比台基为土层的其他台站小一些。② 入射角在40°以上和以下范围, Nakamura方法得到的场地响应形态有差异, 但在各自范围内, 场地响应与入射角的依赖关系不明显。③ 利用同一台站不同时间记录到的地震资料, 由三种方法各自得到的场地响应都具有较好的稳定性; 由于垂直分量仍具有放大作用(在10 Hz以下), Moya的结果大于Nakaruma的结果, 但两者形态上一致性较好; 参考台站法由于受参考台站的影响, 计算得到的场地响应形态和其他两种方法差异较大。④ Moya方法是依赖于震源模型的方法, 它能给出绝对的场地响应值, 其它两种方法的结果是一种相对场地响应, 受参考对象的影响较大。     

核设施一维土层地震反应分析中的参数不确定性

本文概述了一维土层地震反应分析等效线性化方法评价结果不确定性研究的进展,比较了中美两国核设施土层地震反应分析中参数不确定性的处理方法。基于实测数据,令参数随机变化,建立土层剖面模型,采用随机振动理论方法,分析了土层动力特性、剪切波速、基岩地震动输入界面对评价结果的影响。结果表明,土层剪切波速的不确定性对评价结果影响最大,主要表现为加速度反应谱平台段的延长。对比参数随机变化模型和最佳估计模型的计算结果可知,随机振动理论反映了土层对基岩地震动的影响,将随机模型分析结果的中值加减1倍标准差基本可以包络最佳估计模型的分析结果。     

PART II: Comparison of Theoretical and Experimental Estimations of Site Effects

— To check the reliability and the quality of the theoretically estimated ground responses obtained from the 2-D simulation by the application of the hybrid method in PART-I, we compare some of them with those obtained at the same sites from observed data using the Standard Spectral Ratio (SSR). The comparison validates our synthetic modeling and shows that in cases of complex geometries, the use of at least 2-D numerical simulations is required in order to reliably evaluate site effects and thus facilitate the microzonation of the city of Thessaloniki.     

运用谱比法计算福建地区观测台网台站响应

场地动力特性对地震造成的破坏有着重要的影响。因此对场地进行动力特性分析,对于地震的监测预报、地震预警、工程抗震设防、地震勘探等具有十分重要的意义。本文主要结合福建地区现有地震观测台网,利用地脉动记录,采用较为简便的谱比方法（Nakamura方法）对福建地区观测台网中台站响应情况进行计算和分析。     

Site response in Tecoman,Colima, Mexico—I: Comparison of results from different instruments and analysis techniques

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.     

Site characterizations for the Iranian strong motion network

Twenty-six sites of the Iranian strong motion network, having provided numerous records of good quality, were selected for a site effect study with the objective of obtaining a reliable site categorization for later statistical work on Iranian strong motion data. For each site, superficial Vp and Vs profiles were measured with refraction techniques, microtremor recordings were obtained and analysed with the H/V technique and the available three-component accelerograms by the receiver function technique. The aggregation of these results allows the proposition of a four-class categorization based on the H/V spectral ratio of strong ground motions, which demonstrate a satisfactory correlation with the S-wave velocity profile. Iran has a particular geological and meteorological situation compared to other seismic countries such as Japan or California, a mountainous country with dry weather conditions and a low water table in most areas. These conditions result in a relatively small number of sites with low frequency amplification, while many sites exhibit moderate amplifications in the intermediate and high frequency range.     

内马铁路一期工程局部不规则二维场地地震反应分析

基于内马铁路一期工程地质资料,利用ABAQUS有限元软件建立某局部不规则二维场地有限元计算模型,利用Python语言进行二次开发,编制二维等效线性化计算程序。开展50年超越概率63%、10%和2%水准下的土层地震反应分析计算,对不规则地形不同位置处的地震动峰值加速度和频谱特性进行对比分析。研究结果表明,不规则地形对地震动特性的影响显著。本文研究结果对内马铁路一期工程地震动参数确定具有指导意义,同时可为跨越不规则地形工程结构抗震设计提供参考。     

Site Response and Earthquake Design Spectra for Central Khartoum, Sudan

Khartoum, the capital of Sudan, is located at the confluence of White and Blue Niles. The city is heavily populated. Central Khartoum with its high-rise buildings is the center of governmental and business activities and is located on a strip adjacent to the Blue Nile. Geological and geotechnical data indicate that the subsoil conditions at Central Khartoum are characterized by alluvial deposits underlain by Nubian Sandstone at a depth of 25 m. The alluvial deposits, locally known as Gezira formations, consist of clays grading into silt and sand with depth. Macro seismic zonation of Sudan and its vicinities, developed by the authors, gave the ground acceleration at the bedrock surface. The effect of alluvial deposits in Central Khartoum on propagation of seismic motion parameters to the ground surface is investigated in this study. Correlations are proposed for pertinent cyclic soil properties such as shear modulus, damping, and shear wave velocity. The Equivalent-Linear Earthquake Response Analyses (EERA) Model was used to study the effect of local soil conditions on ground-motion parameters. In the absence of strong-motion records in Khartoum, available worldwide strong-motion records are used. Plots showing the time histories of ground motion parameters at the ground surface are obtained. The results indicate amplification of ground motion of up to 4.93. The predicted fundamental period of soils is about 0.5 s which is typical for these types of soils. The maximum spectral acceleration varied from 0.76 to 0.95 g. For design purposes, a response spectrum curve is proposed.     

基于一种新显式时间积分算法的场地非线性地震反应分析

针对线弹性结构动力学方程,作者已提出一种具有良好稳定性的二阶精度单步显式时间积分算法。本文将该方法推广到求解材料非线性结构动力学方程中,采用带误差控制的修正欧拉算法计算单元应力,提高显式时间积分算法的精度。将求解非线性问题的显式算法应用于地震波垂直入射时非线性地震反应分析中,使用黏性边界模拟场地土层底部半空间基岩的辐射阻尼,并考虑地震动输入。与中心差分法计算结果进行对比,以表明新显式算法的有效性。     

用广义反演方法估算首都圈地区台站场地效应

本文利用2001—2006年首都圈地区的SH波数字化地震资料, 用广义逆矩阵联合反演的方法得到了63个台站的场地效应值。 基岩场地的场地效应比较稳定, 在1～10 Hz范围内为1左右; 沉积场地在低频场地效应较高, 在1～8 Hz范围内在3～7之间, 5 Hz左右场地效应有明显的突起, 以后随频率增加降低。 结果表明, 台站岩性是影响场地效应形态和大小的主要因素, 此外其场地效应还可能与所处的局部地质构造等因素有关。     

基于谱比法的江苏强震动台站场地特征分析

选取江苏省强震动台网近年来获得的强震动记录,基于水平竖向谱比法(HVSR),计算了22个强震动台站的速度反应谱平均谱比曲线,采用谱比形状一致法进行场地分类,并结合典型台站场地的工程地质资料进行对比分析。研究结果表明,平均谱比曲线的卓越周期、场地放大等特征与台站场地地质资料相吻合,与传统场地分类方法相比,基于谱比法的场地特征分类方法能够突出不同场地的地震动反应特征,较好地体现了台站的场地反应特征。     

三河—平谷地区地脉动H/V谱比法探测:场地响应、浅层沉积结构及其反映的断层活动

1679年三河—平谷8级地震,造成了包括北京在内的华北广大地区严重的人员和经济损失,但是该地区和地震灾害密切相关的沉积结构和地震场地响应特征研究,相对比较缺乏.本文利用1~4 km台间距的高密度单台地脉动观测、几个小孔径台阵观测和钻孔测井数据,研究了三河—平谷地区的浅层沉积的场地响应和沉积层三维起伏特征,以及构造运动对沉积厚度的影响.结果表明,研究区沉积层的场地共振频率和沉积厚度有明显的分区特征：东北部场地共振频率主要在1.0~7.0 Hz之间,具有相对较薄的沉积厚度,沉积界面起伏也相对平稳;西南部场地共振频率大部分区域小于1.0 Hz,可低至0.3 Hz,相应的沉积厚度起伏显著,其中在大厂凹陷厚度可达300~600 m.沉积起伏和隐伏断裂带的分布有较好的对应关系,反映了夏垫断裂、南苑—通县断裂第四纪以来较为活跃的正断活动.北东走向的夏垫等隐伏断裂在东北部山前的正断活动相对不发育,以及东北部和西南部沉积厚度的显著差异,都可能受到北西走向的二十里长山断裂带活动的影响.按照Vs30场地分类,研究区内沉积较厚的凹陷地区主要为E类软土,其他区域为D类中硬土.研究结果与区域地质调查、钻孔数据和浅层地震勘探剖面结果基本相符,说明地脉动探测方法能够高效、低成本的获取区域沉积厚度和场地作用,为地震小区划和抗震设防提供有意义的参考.

     

三河—平谷地区地脉动H/V谱比法探测:场地响应、浅层沉积结构及其反映的断层活动

1679年三河—平谷8级地震,造成了包括北京在内的华北广大地区严重的人员和经济损失,但是该地区和地震灾害密切相关的沉积结构和地震场地响应特征研究,相对比较缺乏.本文利用1~4 km台间距的高密度单台地脉动观测、几个小孔径台阵观测和钻孔测井数据,研究了三河—平谷地区的浅层沉积的场地响应和沉积层三维起伏特征,以及构造运动对沉积厚度的影响.结果表明,研究区沉积层的场地共振频率和沉积厚度有明显的分区特征：东北部场地共振频率主要在1.0~7.0 Hz之间,具有相对较薄的沉积厚度,沉积界面起伏也相对平稳;西南部场地共振频率大部分区域小于1.0 Hz,可低至0.3 Hz,相应的沉积厚度起伏显著,其中在大厂凹陷厚度可达300~600 m.沉积起伏和隐伏断裂带的分布有较好的对应关系,反映了夏垫断裂、南苑—通县断裂第四纪以来较为活跃的正断活动.北东走向的夏垫等隐伏断裂在东北部山前的正断活动相对不发育,以及东北部和西南部沉积厚度的显著差异,都可能受到北西走向的二十里长山断裂带活动的影响.按照Vs30场地分类,研究区内沉积较厚的凹陷地区主要为E类软土,其他区域为D类中硬土.研究结果与区域地质调查、钻孔数据和浅层地震勘探剖面结果基本相符,说明地脉动探测方法能够高效、低成本的获取区域沉积厚度和场地作用,为地震小区划和抗震设防提供有意义的参考.     

FIBRE BEAM–COLUMN MODEL FOR NON-LINEAR ANALYSIS OF R/C FRAMES: PART I. FORMULATION

This paper presents a fibre beam–column element for the non-linear static and dynamic analysis of reinforced concrete frames. It is assumed that plane sections remain plane and normal to the longitudinal axis. The effects of shear and bond-slip are, thus, presently neglected. The non-linear hysteretic behaviour of the element derives from the constitutive relations of concrete and reinforcing steel fibres into which each section is divided. The element formulation is flexibility-based and relies on force interpolation functions that strictly satisfy the equilibrium of bending moments and axial force along the element. Since the element does not make use of displacement interpolation functions, an iterative algorithm is needed for the determination of the resisting forces during the element state determination. The proposed algorithm is accurate and stable, even in the presence of strength loss, and is, thus, capable of tracing very well the highly non-linear behaviour of R/C members under cyclic load combinations of bending moment and axial force.     

Estimation of Site Response in Kachchh,Gujarat, India,Region Using H/V Spectral Ratios of Aftershocks of the 2001 <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">w</Emphasis></Subscript> 7.7 Bhuj Earthquake

Site response in the aftershock zone of 2001 Bhuj M_w 7.7 earthquake has been studied using the H/V spectral ratio method using 454 aftershocks (M_w 2.5–4.7) recorded at twelve three-component digital strong motion and eight three-component digital seismograph sites. The mean amplification factor obtained for soft sediment sites (Quaternary/Tertiary) varies from 0.75–6.03 times for 1–3 Hz and 0.49–3.27 times for 3–10 Hz. The mean amplification factors obtained for hard sediment sites (hard Jurassic/Mesozoic sediments) range from 0.32–3.24 times for 1–3 Hz and 0.37–2.18 times for 310 Hz. The upper bounds of the larger mean amplification factors for 1–3 Hz are found to be of the order of 3.13–6.03 at Chopadwa, Vadawa, Kavada, Vondh, Adhoi, Jahwarnagar and Gadhada, whereas, the upper bounds of the higher mean amplification factors at 3–10 Hz are estimated to be of the order of 2.00–3.27° at Tapar, Chopadwa, Adhoi, Jahwarnagar, Gandhidham and Khingarpur. The site response estimated at Bhuj suggests a typical hard-rock site behavior. Preliminary site response maps for 1–3 Hz and 310 Hz frequency ranges have been prepared for the area extending from 23–23.85 °N and 69.65–70.85°E. These frequency ranges are considered on the basis of the fact that the natural frequencies of multi-story buildings (3 to 10 floor) range between 1–3 Hz, while the natural frequencies for 1 to 3 story buildings vary from 3–10 Hz. The 1–3 Hz map delineates two distinct zones of maximum site amplification (>3 times): one lying in the NW quadrant of the study area covering Jahwarnagar, Kavada and Gadadha and the other in the SE quadrant of the study area with a peak of 6.03 at Chopadwa covering an area of 70 km × 50 km. While the 3–10 Hz map shows more than 2 times site amplification value over the entire study area except, NE quadrant, two patches in the southwest corner covering Bhuj and Anjar, and one patch at the center covering Vondh, Manfara and Sikara. The zones for large site amplification values (∼3 times) are found at Tapar, Chopadwa, Adhoi and Chobari. The estimated site response values show a good correlation with the distribution of geological formations as well as observed ground deformation in the epicentral zone.     

Site effects at Euroseistest—I. Determination of the valley structure and confrontation of observations with 1D analysis

This paper describes the process of construction of the 2D model of Volvi's geological structure and results of empirical and theoretical approaches to the evaluation of site response at Euroseistest. The construction of the 2D model is based on a re-interpretation of the available geophysical and geotechnical data in an effort to improve the definition of the subsoil structure at Euroseistest in terms of the most important parameters needed to model site response. The results of this re-interpretation are compared with a previous published 2D model of the same alluvial valley. Different analysis of the measurements and different criteria in the synthesis of data have led to a different model, even if both studies had access to the same field measurements. This underscores the fact that a model results of an interpretation and is not uniquely determined by the data, no matter how detailed they are. The well known subsoil structure opened the possibility to correlate the geometry and the dynamic properties of the 2D model with the results of site response determined from a detailed analysis of two events in frequency and time domains and 1D numerical modeling. The study of site response shows the important effect of the lateral variations on the ground motion and suggests that the contribution of locally generated surface waves to the resonant peak may be important. In the case of Volvi's graben, the limitations of the 1D approximation to simulate ground motion under complex soil conditions in both frequency and time domains are also shown. This paper lays the ground for a companion article dealing with 2D site effects in this basin.     

A Discrete Wavenumber Boundary Element Method for study of the 3-D response 2-D scatterers

A mathematical formulation of the 2·5D elastodynamic scattering problem is presented and validated. The formulation is a straightforward extension of the Discrete Wave number Boundary Integral Equation Method (DWBIEM) originally proposed by Kawase¹ for 2D scattering problems and subsequently extended to the 3D problem by Kim and Papageorgiou.² It is demonstrated that the Green's function which is appropriate for a boundary formulation of the 2·5D elastodynamic scattering problem is the one corresponding to a unit force moving on a straight line with constant velocity. Such a Green's function is derived in the present study. The formulation may be used to study the wavefields in models of sedimentary deposits (e.g. valleys) or topography (e.g. canyons or ridges) with a 2D variation in structure but obliquely incident plane waves. The advantage of a 2·5D formulation is that it provides the means for calculations of 3D wavefields in scattering problems by requiring a storage comparable to that of the corresponding 2D calculations. © 1998 John Wiley & Sons, Ltd.     

Complex Site Effects in Thessaloniki (Greece): II. 2D SH Modelling and Engineering Insights

This paper presents results of numerical modelling of site response for Thessaloniki, obtained with two different 2D methods; a finite difference and a finite element method. Ground motion across a 2D model of the subsoil of the city has been simulated for vertically incident SH waves. The predominance of locally generated surface waves is very clear in the synthetic seismograms of a weak event and of stronger ones. These results are then compared with the observations in time domain and frequency domain. The role of the soil formations with high attenuation in the lateral propagation and the effect of the differential motion close to the lateral variations are also pinpointed. The stronger events were finally used to compute strong ground motion in order to reveal and to discuss practical engineering aspects such as peak ground acceleration value, the most familiar indicator in seismic norms, the soil to rock spectral coefficients for the period bandwidth of interest, and the aggravation factor in terms of 2D to 1D response spectra as a useful ruler to account for complex site effects.