翡翠河谷地震动地形效应解析分析

地表不规则地形的存在往往会引起地震波的散射,进而产生局部地震动放大或衰减的现象.虽然地形效应最早在异常地震记录中被发现,然而利用地形影响台阵记录到的地震动数据却少之又少.基于1992年在我国台湾翡翠河谷上观测到的六条地形影响台阵记录,利用线源SH波入射下非对称V形河谷地震波传播解析理论,模拟得到了河谷台阵各点的地震动,...     

Slope topography effects on ground motion in the presence of deep soil layers

An extensive investigation has been made into the interaction between topographic amplification and soil layer amplification of seismic ground motion. This interaction is suggested in the literature as a possible cause for the differences between topographic amplification magnitudes observed in field studies and those obtained from numerical analysis. To investigate this issue a numerical finite element (FE) parametric study was performed for a slope in a homogeneous linear elastic soil layer over rigid bedrock subjected to vertically propagating in-plane shear waves (Sv waves). Analyses were carried out using two types of artificial time history as input excitation, one mimicking the build-up and decay of shaking in the time histories of real earthquake events, and the other to investigate the steady-state response. The study identified topographic effects as seen in previous numerical studies such as modification of the free-field horizontal motion, generation of parasitic vertical motion, zones of alternating amplification and de-amplification on the ground surface, and dependence of topographic amplification on the frequency of the input motion. For the considered cases, topographic amplification and soil layer amplification effects were found to interact, suggesting that in order to accurately predict topographic effects, the two effects should not be always handled separately.     

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅰ)

Amplification of in-plane seismic ground motion by underground group cavities in layered half-space is studied both in frequency domain and time domain by using indirect boundary element method (IBEM), and the effect of cavity interval and spectrum of incident waves on the amplification are studied by numerical examples. It is shown that there may be large interaction between cavities, and group cavities with certain intervals may have significant amplification to seismic ground motion. The amplification of PGA (peak ground acceleration) and its PRS (peak response spectrum) can be increased up to 45.2% and 84.4%, for an example site in Tianjin, under the excitation of Taft wave and El Centro wave; and group cavities may also affect the spectra of the seismic ground motion. It is suggested that the effect of underground group cavities on design seismic ground motion should be considered.     

局部山体地形对强地面运动的影响研究

基于曲线网格有限差分方法研究了地震波在不同坡度的山体地形及水平地表模型中的传播,得到了各模型速度波形及地表峰值速度特征,从地形自身特征及震源特征两方面出发讨论了地形效应:一是相同的震源模型下地形坡度、形状对地震动的影响;二是同一山体模型下地震动对不同震源机制的点源以及相对复杂的有限断层的响应.主要结论如下:(1)一般情况下,地形放大效应在坡度较大的地方比较明显,并随着坡度的增加而增大,但在某些特定情况下,放大效应与坡度并不满足正相关,且这种情况的发生与震源性质无关,可能仅受地形形态自身的影响;(2)对于不同的震源机制,地面运动各分量受地形影响程度不同,总体上水平分量受地形影响程度更大;(3)震源机制和震源激发的波的频率会影响放大效应最大值出现的位置,放大效应最大值不一定出现在山顶处,有可能会出现在起伏地形的震源对侧,出现位置可能与波的相互作用有关;(4)有限断层模型下,地面运动特征相对更为复杂,地形效应不仅受断层模型几何特征的影响,同时断层破裂过程对其也有着重要的影响.     

A new solution to estimate the time delay on the topographic site using time domain 3D boundary element method

This study focuses on investigating spatial variation of ground motion that has great influence on the dynamic behavior of the large structures located on the surface topography. One of the most effective parameters on the spatial variation of ground motion is the difference between the arrival time of seismic waves in different points located on the abutments. In this research, a three-dimensional model of the Pacoima Dam site is prepared. The time domain 3 D boundary element method is used to apply non-uniform excitation at the dam supports. This model is subjected to vertically propagating incident SH and P waves. The time delay can be characterized by calculating the value of the time delay for which the cross-correlation between two records is maximized. Finally, to obtain the time delay in a topographic site, a function considering effective parameters such as the height from the canyon base, wave velocity and predominant frequency, is presented. Furthermore, a code was developed for generating the spatially variation of seismic ground motions. The results show that the proposed functions have an acceptable accuracy in estimating the time delay to generate non-uniform ground motion.     

2017年九寨沟MS7.0地震场地特征分析

场地条件对地震动具有较大影响, 研究不同场地条件下的地震动特征对地震动的校正具有重要意义。 本文以九寨沟地震为例, 收集了66个台站的198条三分量强震观测记录和SRTM(Shuttle Radar Topography Mission)公里格网的DEM(Digital Elevation Model)数据, 从多个角度对场地特征进行分析。 首先根据坡度法使用DEM数据对九寨沟特征进行了场地分类, 然后讨论了不同场地类型下的加速度时程、 加速度反应谱、 地震动衰减等地震动特征。 研究表明, 缺少实测资料的情况下, 地形坡度可以作为Vs30(地表以下30 m范围的平均剪切波速度)的一种替代指标, 利用坡度法可以较快速地对场地进行分类; 利用强震观测记录能够从多角度对台站的场地特征进行分析, 不同场地类型对地震动影响不同, 其中, 土层对地震动具有明显的放大效应。 该结论可以为地震动结果的校正提供依据。     

风化半圆形河谷对柱面SH波的散射解析解

风化河谷地震效应对建在此类场地上工程结构(如大坝、桥梁)的动力稳定性具有潜在的威胁,为揭示河谷风化层对地面运动的影响,利用波函数展开法推导风化半圆形河谷对线源柱面SH波散射问题的解析解。计算不同震源位置条件下风化半圆形河谷的地表位移反应和地面运动放大因子,分析地面运动的幅值和形态,发现随着震源距离的增大,在河谷附近地震动的放大和衰减的交替更频繁。     

Simulation of Ground Motion from Strong Earthquakes of Kamchatka Region (1992–1993) at Rock and Soil Sites

To estimate the parameters of ground motion in future strong earthquakes, characteristics of radiation and propagation of seismic waves in the Kamchatka region were studied. Regional parameters of radiation and propagation of seismic waves were estimated by comparing simulations of earthquake records with data recorded by stations of the Kamchatka Strong Motion Network. Acceleration time histories of strong earthquakes (M _w = 6.8–7.5, depths 45–55 km) that occurred near the eastern coast of Kamchatka in 1992–1993 were simulated at rock and soil stations located at epicentral distances of 67–195 km. In these calculations, the source spectra and the estimates of frequency-dependent attenuation and geometrical spreading obtained earlier for Kamchatka were used. The local seismic-wave amplification was estimated based on shallow geophysical site investigations and deep crustal seismic explorations, and parameters defining the shapes of the waveforms, the duration, etc. were selected, showing the best-fit to the observations. The estimated parameters of radiation and propagation of seismic waves describe all the studied earthquakes well. Based on the waveforms of the acceleration time histories, models of slip distribution over the fault planes were constructed for the studied earthquakes. Station PET can be considered as a reference rock station having the minimum site effects. The intensity of ground motion at the other studied stations was higher than at PET due to the soil response or other effects, primarily topographic ones. At soil stations INS, AER, and DCH the parameters of soil profiles (homogeneous pyroclastic deposits) were estimated, and nonlinear models of their behavior in the strong motion were constructed. The obtained parameters of radiation and propagation of seismic waves and models of soil behavior can be used for forecasting ground motion in future strong earthquakes in Kamchatka.     

山脊地形效应的强震动观测研究

根据强震动观测、实验研究与数值模拟结果表明,山脊地形对地震动具有显著影响.文章基于汶川地震主震及余震的三个地形效应观测台阵记录的三分量地震动加速度时程,经基线校正后计算得到各观测点的地面峰值加速度、峰值加速度比和反应谱比,分析山脊地形对地震地面运动的影响.结果表明:山脊地形对地震地面运动的影响显著,其地形地震效应随山脊地形的不同而变化,且地形效应具有方向性;水平向地形效应显著于垂直向;谱比是周期相关的,在所分析的周期范围内谱比不总是大于1．0.     

黄土丘陵河谷场地地震动特征研究

研究黄土丘陵河谷场地在地震作用下强地面运动特征的变化情况,可以揭示强震对该类场地上震害的触发机理。结合黄土高原的地貌特征,建立具有代表性的动力数值分析模型,通过输入不同幅值、频谱特性和持续时间的地震波,对起伏地形和覆盖黄土层共同影响下的黄土河谷场地进行地震反应分析。结果表明:黄土层和地形耦合作用控制了地表的PGA变化,使其趋于复杂,在同一输入波不同振幅作用下,与基岩河谷各测点相比,黄土覆盖河谷场地的地震动频谱幅值均有所增加,并且频谱主峰均向高频移动。在不同地震波输入下,场地不同部位的固有频率受地形高程和土层影响;而地震动大小和频谱幅值不仅与场地的基本频谱和地形起伏有关,也与输入地震波的频谱成分相关。输入波PGA与地震频谱特征都不变时,同一场地输出的地震频谱形状具有相似的特征,随着地震持时增长,能量向场地基本频率附近集中,从而可能导致场地上相应频率建筑物震动幅值增加,造成累积破坏。     

SV波全反射作用下地震动的合成及振动特性

越来越多的研究表明来自基岩的地震波并不是垂直地面向上传播的。地震波在斜入射与垂直入射时所产生的场地效应有很大不同,由于存在全反射现象,SV波在斜入射时产生的场地效应更为复杂。文章基于均匀弹性半空间地震波传播理论,分别推导得到SV波入射角在小于、大于等于临界角时地震动的计算表达式,通过模型算例研究SV波全反射作用下的地震动特性。研究发现：由SV波产生的地震动主要由入射波和反射波构成,滑行波作用可以忽略;地面运动轨迹具有面波旋转振动特点;随着入射角的增大,地面震动从以水平方向振动为主逐渐过渡到以垂直方向振动为主,两个方向的振动均小于入射波峰值的2倍。     

Application of numerical wave-propagation techniques to study local soil effects: The case of Benevento (Italy)

Many of the numerical techniques used for seismic zonation studies treat one-dimensional structural models and/or the incidence of plane polarized body waves. These techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest. In such cases a more rigorous treatment of the combined effects of the source, the path and the site response is needed. This can be accomplished with a hybrid approach combining modal summation and the finite-difference technique. To demonstrate the differences between these techniques, the ground motion in the city of Benevento (Italy) is modelled. We first compare the results obtained with one-and two-dimensional structural models for vertical incidence of plane polarized body waves. These results are then compared with those obtained with the hybrid approach for two-dimensional structural models.The comparisons have allowed us to find important differences in the response obtained with the different modelling techniques. For the same site, these differences consist of strong variations in amplitude and in the shape of the spectral amplifications. For a seismic source which is not located beneath the site, vertical incidence of waves significantly overestimates the local hazard in a laterally homogeneous structure. For a laterally heterogeneous area, we can conclude that one-dimensional modelling fails to estimate the seismic hazard, whereas for a seismic source which is not located beneath the site of interest, two-dimensional modelling with vertical incidence of plane polarized body waves may not allow reliable estimates to be made of the frequency bands at which amplifications occur. The results obtained for two-dimensional structural models are used for a zonation of the city of Benevento.     

Effects of near-fault and far-fault ground motions on nonlinear dynamic response and seismic damage of concrete gravity dams

As the forward directivity and fling effect characteristics of the near-fault ground motions, seismic response of structures in the near field of a rupturing fault can be significantly different from those observed in the far field. The unique characteristics of the near-fault ground motions can cause considerable damage during an earthquake. This paper presents results of a study aimed at evaluating the near-fault and far-fault ground motion effects on nonlinear dynamic response and seismic damage of concrete gravity dams including dam-reservoir-foundation interaction. For this purpose, 10 as-recorded earthquake records which display ground motions with an apparent velocity pulse are selected to represent the near-fault ground motion characteristics. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The Koyna gravity dam, which is selected as a numerical application, is subjected to a set of as-recorded near-fault and far-fault strong ground motion records. The Concrete Damaged Plasticity (CDP) model including the strain hardening or softening behavior is employed in nonlinear analysis. Nonlinear dynamic response and seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. Both local and global damage indices are established as the response parameters. The results obtained from the analyses of the dam subjected to each fault effect are compared with each other. It is seen from the analysis results that the near-fault ground motions, which have significant influence on the dynamic response of dam–reservoir–foundation systems, have the potential to cause more severe damage to the dam body than far-fault ground motions.     

地震动空间效应对大跨度桥梁非线性地震响应的影响

由于大跨度桥梁的桥墩间距离较大,其地震响应分析应考虑地震动输入的空间效应。本文建立了多点激励下大跨度桥梁地震响应分析方法,采用损伤塑性本构模型模拟混凝土材料特性,考虑地震动空间效应对大跨度连续刚构桥进行非线性地震响应分析,从而分析地震动空间效应对大跨度桥梁地震响应的影响。研究表明:考虑行波激励或多点激励时桥梁地震响应较一致激励而言有所差异,考虑地震动空间效应时可能会夸大或减小桥梁结构的动力响应;多点激励时桥梁地震响应会随视波速的改变而变化。由此得出结论,对于大跨度桥梁地震响应分析应合理的考虑地震动空间效应。     

A brief theory and computing of seismic ground rotations for structural analyses

The seismic ground rotations are important with respect to spatial structural models, which are sensitive to the wave propagation. The rotational ground motion can lead to significant increasing of structural response, instability and unusual damages of buildings. Currently, the seismic analyses often take into account the rocking and torsion motions separately using artificial accelerograms. We present an exact analytical method, proposed by Nazarov [15] for computing of three rotational accelerograms simultaneously from given translational records. The method is based on spectral representation in the form of Fourier amplitude spectra of seismic waves, corresponding to the given three-component translational accelerogram. The composition, directions and properties of seismic waves are previously determined in the form of a generalized wave model of ground motion. It is supposed that seismic ground motion can be composed by superposition of P, SV, SH- and surface waves. As an example, the dynamic response analysis of 25-story building is presented. Here recorded (low-frequency) and artificial (high-frequency) accelerograms were used; each of them includes three translational and three rotational components. In this structural analysis, we have clarified primarily conditions under which rotational ground motion should be taken into account. Next, we have calculated three rotational components of seismic ground motion. Then they were taken as additional seismic loads components for further seismic analysis of the building. Note, soil–structure interaction (SSI) is not considered in this study. For computing, we use the special software for structural analyses and accelerogram processing (FEA Software STARK ES and Odyssey software, Eurosoft Co., Russia). It was developed and is used in engineering practice in the Central Research Institute of Building Constructions (TsNIISK, Moscow, Russia).     

不同倾角断层对场地动力放大效应的分析

一般认为断层有一定的隔震作用,但是也有不少震害表明断层附近的破坏反而比较严重。为探讨其中机理,采用有限元方法分别建立包含不同倾角无厚度断层的场地模型,并分析了在各种频率入射波的作用下该场地的动力反应。计算结果表明,断层对场地的动力反应有一定的放大作用,特别是当入射波的频率与场地的基频接近时,放大效应更为明显。计算结果还表明,断层的倾角对场地的动力反应也有影响,随着断层倾角的减小,断层出露点附近的动力放大效应增大。     

浅硬场地剪切波速测试标准差对地震动影响初探

采用Shake 2000程序,以Turkey Flat试验场地为模型,通过输入不同类型下多种强度的地震波,计算研究多工况下剪切波速测试标准差对地表加速度反应谱和峰值加速度的影响。结论为:(1)浅硬场地上剪切波速测试标准差对地震动的影响很大,影响程度与输入地震波的强度和频率以及场地剪切波速计算值有关;(2)如果将反应谱残差大于20%或加速度峰值差别大于20%定义为统计意义上的不可忽略,那么剪切波速测试标准差对计算结果的影响在大多数情况下均不可忽略;(3)当输入波的卓越周期与场地特征周期接近时,浅硬场地上剪切波速测试标准差引起的反应谱变化非常显著;(4)只有当输入波的卓越周期与场地特征周期相差较大且输入波强度偏小时,剪切波速测试标准差引起的反应谱变化才可略去;(5)当浅硬场地上剪切波速实测结果低于统计均值时,地震动计算结果的偏差一般明显大于剪切波速实测结果,高于统计均值时引起的偏差,且地震输入越强表现越明显。     

Scattering of plane sh waves by a semi-cylindrical hill

A new analytical method is presented to study the problem of scattering of plane SH waves by a semi-cylindrical hill in an otherwise homogeneous, isotropic and elastic two-dimensional half-space, using the series of wave functions and a new expansion technique. The results obtained show that (1) the hill has quite considerable effects on ground motions for both the points on the hill and its environs, (2) these effects depend mainly on the frequency, the angle of wave incidence and the ratio of radius of hill to one-half the wave length of incident waves, and (3) prominent and depression topographies having equal form and radius for the same incident waves would cause quite different mechanisms of wave propagation in both response performance and magnitude. The results, doubtless, would be useful for further deepening knowledge of the effects of prominent topography on seismic ground motion and for testing the accuracy of various approximate methods so far available.     

一种利用单台强震记录计算任意场地三分量地面运动的方法

本文利用近场理论格林函数反褶积的方法计算土层的地震反应.解答中包含了产生地面运动的各种反射、透射和转换波震相,也计入了土层与基底介质的相互作用.将计算的土层响应与已获得的近场加速度记录褶积,可算出不同土层场地上垂直向和水平向三分量的地面运动.文中利用1982年卢龙地震的近场加速度记录,检验了方法的可行性.     

一种利用单台强震记录计算任意场地三分量地面运动的方法

本文利用近场理论格林函数反褶积的方法计算土层的地震反应.解答中包含了产生地面运动的各种反射、透射和转换波震相,也计入了土层与基底介质的相互作用.将计算的土层响应与已获得的近场加速度记录褶积,可算出不同土层场地上垂直向和水平向三分量的地面运动.文中利用1982年卢龙地震的近场加速度记录,检验了方法的可行性.