地脉动机制分析方法研究

本文首先回顾了地脉动波场分析方法的发展历史和以往研究地脉动机制的几种方法。然后依据作者对基岩地脉动水平分量与竖向分量谱比的理论分析结果，结合地脉动记录的运动学和动力学特征，提出了判定地脉动波场性质的形态法，轨迹法和基岩地脉动谱比法，并用实际地脉动观测记录对这3种方法进行了验证。     

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.     

利用地脉动进行场地反应分析研究综述

介绍了应用地脉动进行场地反应分析的几种主要方法,概述了应用地脉动进行场地反应分析的现状,分析了各种方法的适用条件及存在的问题,针对其中的某些问题提出了可能的解决方法。     

采用FDTD方法模拟三种简单沉积结构模型的脉动H/V响应

利用地脉动进行地球物理无源探测技术,并基于地脉动观测的水平分量与竖直分量谱比法(H/V),获取沉积层卓越频率和沉积盖层厚度已得到较广泛的应用。本文从正演的角度出发,分别建立了水平层状、倾斜层状和不均匀构造三种由简单到复杂的模型,采用时域有限差分方法(FDTD)模拟地脉动随机源的探测数据,将数值模拟获得的数据利用H/V谱比法(Nakamura方法)进行反推,与原模型设置值相对比符合良好,表明FDTD的全波正演能很好地模拟获得各种模型在随机源激发下产生的稳定波场信息,为应用地脉动探测研究城市沉积层提供了科学的依据。     

祁连山主动源观测台站场地响应分析

场地响应是精确测定震源参数和稳健估计出高精度地壳介质衰减变化的关键影响因素之一,采用H/V尾波谱比法,对祁连山主动源观测台网中40个短周期观测台站的场地响应进行了分析.结果表明,祁连山主动源观测台网中40个短周期观测台站均存在不同程度的放大(衰减)作用,根据40个台站观测波形的尾波场地响应曲线特征,可将其分为平坦类、放...     

应用微动H/V谱比法和台阵技术探测场地响应和浅层速度结构

为了快速而且廉价地获取北京市详细的场地响应和浅层速度结构,应用于地震动模拟和地震灾害预防,我们开展了微动观测技术和处理方法研究.本文利用2007年夏季北京五棵松地区进行的几个微动观测实验数据,使用单台H/V谱比法分析场地的卓越频率及其对应的放大系数,并对比了不同地震仪和观测时间对H/V曲线的影响;应用高分辨率F-K频谱分析方法从微动台阵数据中得到Rayleigh波的频散曲线并使用邻域算法反演出浅层速度结构.H/V结果表明该地区卓越频率在2.1～2.2 Hz之间,对应的放大系数下限约为3;利用微动H/V方法得到的场地卓越频率具有较高的稳定性.微动台阵反演结果给出了比较合理的波阻抗界面深度和层平均速度结构,认为地下80多米处的波阻抗界面是决定场地卓越频率和其场地放大系数的主要界面.本研究表明微动技术应用于评估城市地震场地响应和浅层速度结构是可行且易于实施的.     

地脉动方法最新研究进展

因其简便、经济的独特优势,地脉动方法在场地动力性能评价中得到了国际学术界广泛关注,业已取得了大量的研究成果和并得到了广泛应用。由于对国际地脉动研究的最新进展缺乏足够的了解,我国地震工程界对其研究和应用尚存在不同认识。本文着重介绍了地脉动单点谱比法和地脉动台阵方法的国际最新研究进展和实践现状,指出了各种方法的特点及其应用条件,以期促进地脉动方法在我国的合理使用,推动我国地脉动研究的不断深入。     

安徽省国家强震动台站场地响应及背景噪声分析

利用安徽省部分强震动台站记录的地脉动数据和历史地震数据,采用H/V谱比法和噪声功率谱密度函数法,对比分析台站的场地响应及背景噪声,结果表明：全椒、马鞍山地震台的场地卓越周期小且背景噪声低;沈巷地震台卓越周期大且背景噪声高;三山地震台无明显卓越周期;地震台站背景噪声与场地响应曲线之间不存在一一对应关系。     

Applicability of the H/V spectral ratio of microtremors in assessing site effects on seismic motion

The authors examine the reliability of site response estimations obtained by the horizontal to vertical (H/V) spectral ratios of microtremors by means of cross‐validation with the ratio of the horizontal spectra of earthquake motion with respect to reference sites. The data comprise microtremor and ground motion records recorded at 150 sites of Yokohama strong motion array. The use of non‐supervised pattern recognition techniques aims to group the sites with more objectivity. Attributes defining the overall shape of the amplification spectra serve as input in the computation of Euclidean distance similarity coefficients amongst sites. The implementation of the Ward clustering scheme leads to the attainment of a meaningful tree diagram. Its analysis shows the possibility of summarizing the results into six general patterns. A good coincidence of site effects estimates at 80 per cent of the sites becomes apparent. However, this coincidence appears poor for sites characterized by H/V amplification ratios around 2 or smaller and predominant periods longer than 0.5 s. In such cases, the presence of stiff, sandy sediments in the soil profile proves common. To proscribe H/V estimations, relying solely on the small spectral ratios criterion seems inadequate. Copyright © 2001 John Wiley & Sons, Ltd.     

Reliability of Ambient Noise Horizontal-to-Vertical Spectral Ratio in Urban Environments: The Case of Thessaloniki City (Northern Greece)

In the framework of an ambient noise measurement project in the downtown district of the City of Thessaloniki (Northern Greece), several tests and evaluation of noise recordings were performed in selected sites. This data set was processed and compared with previous results for the same sites in terms of horizontal-to-vertical (H/V) spectral ratio obtained from weak and strong motion earthquake data. The recording system used was tested against a reference one. Finally, systematic ambient noise measurements were performed at eight sites in the citys downtown area, to evaluate diurnal and seasonal variations. It was concluded that the recording system used was reliable and the ambient noise H/V spectral ratios were in good agreement with relevant results previously obtained. Diurnal variation of the ambient noise H/V spectral ratio showed that it is preferable to perform measurements during the calm hours of the day, when man-made noise is relatively low. However, no systematic seasonal fluctuation effect on the ambient noise H/V spectral ratio was identified.     

Improvement of HVSR technique by self-organizing map (SOM) analysis

Data interpretation is one of the most important and thorny tasks in geosciences. Difficulties occur especially in non-invasive geophysical techniques and/or when the data that have to be analyzed are multidimensional, non-linear and highly noisy. Another important task is to ensure an efficient automatic data analysis, in order to allow a data interpretation as independent as possible from any a priori knowledge. This paper describes the post-processing application of a kind of neural network (self-organizing map, SOM) to the identification of the fundamental HVSR frequency of a given site. SOM results can be represented as two-dimensional maps, with a non-parametric mapping that projects the high dimensional original dataset in a fashion that provides both an unsupervised clustering and a highly visual representation of the data relationships. This innovative application of the SOM algorithm is presented with a case study related to the characterization of a mineral deposit.     

Structural performance of a base-isolated reinforced concrete building subjected to seismic pounding

The effects of seismic pounding on the structural performance of a base-isolated reinforced concrete (RC) building are investigated, with a view to evaluate the influence of adjacent structures and separation between structures on the pounding response. In particular, seismic pounding of a typical four-story base-isolated RC building with retaining walls at the base and with a four-story fixed-base RC building is studied. Three-dimensional finite element analyses are carried out considering material and geometric nonlinearities. The structural performance of the base-isolated building is evaluated considering various earthquake excitations. It is found that the performance of the base-isolated building is substantially influenced by the pounding. The investigated base-isolated building shows good resistance against shear failure and the predominant mode of failure due to pounding is flexural. Copyright © 2012 John Wiley & Sons, Ltd.     

Ambient noise as the new source for urban engineering seismology and earthquake engineering: a case study from Beijing metropolitan area

In highly populated urban centers, traditional seismic survey sources can no longer be properly applied due to restrictions in modern civilian life styles. The ambient vibration noise, including both microseisms and microtremor, though are generally weak but available anywhere and anytime, can be an ideal supplementary source for conducting seismic surveys for engineering seismology and earthquake engineering. This is fundamentally supported by advanced digital signal processing techniques for effectively extracting the useful information out from the noise. Thus, it can be essentially regarded as a passive seismic method. In this paper we first make a brief survey of the ambient vibration noise, followed by a quick summary of digital signal processing for passive seismic surveys. Then the applications of ambient noise in engineering seismology and earthquake engineering for urban settings are illustrated with examples from Beijing metropolitan area. For engineering seismology the example is the assessment of site effect in a large area via microtremor observations. For earthquake engineering the example is for structural characterization of a typical reinforced concrete high-rise building using background vibration noise. By showing these examples we argue that the ambient noise can be treated as a new source that is economical, practical, and particularly valuable to engineering seismology and earthquake engineering projects for seismic hazard mitigation in urban areas.     

Characteristics of earthquake ground motions and the H/V of microtremors in the southwestern part of Taiwan

The relationships between the spectral characteristics of earthquake ground motions and those of micro‐tremors are investigated using the observed data from a dense strong‐motion network consisting of 108 stations in the Yun‐Li, Chia‐Yi and Tai‐Nan areas in southwestern Taiwan. Many high‐quality recordings, including those of the 921 Chi‐Chi earthquake (M_w=7.6), the 1022 Chia‐Yi mainshock (M_L=6.4), the 1022 major aftershock (M_L=6.0), as well as some weak motion events are selected to evaluate site responses. Microtremor measurements are also performed at most ground motion stations. With many stations in the area located on an alluvium structure, however, it is difficult to find good reference stations on rock sites, which therefore necessitates the calculation of single‐station H/V ratios. The predominant frequencies obtained from H/V ratios are consistent with those from spectral ratios. The site characteristics between the strong and weak events are different, however. This implies that a nonlinear effect probably occurred with the strong‐motion events. The main peak in the H/V spectra of the microtremors is in good agreement with the first peak obtained from the spectra of earthquake ground motions. It is reasonable to claim that the main peak reflects the deep underground structure. On the basis of the H/V ratios of the microtremors, it is concluded that the lower predominant frequencies appear in the plain area, while the higher values are near the mountainous region. Copyright © 2002 John Wiley & Sons, Ltd.     

钢筋混凝土空心桥墩的振动台试验研究

为研究空心桥墩的抗震性能及影响参数,对9个不同配筋率、配箍率和轴压比的试件进行振动台试验。研究了不同性能量化参数对破坏现象、加速度响应、动力放大系数、延性和耗能等的影响。结果表明:轴压比和配筋率较小时,裂缝开展较多且位置距墩底相对偏高。增大配筋率,加速度响应、动力放大系数和位移延性系数增大,耗能减小;轴压比的影响与配筋率相反。增大配箍率,加速度响应和动力放大系数减小,位移延性系数和试件耗能增大。可为矩形空心桥墩的抗震设计提供参考。     

On the Limitation of the H/V Spectral Ratio Using Seismic Noise as an Exploration Tool: Application to the Grenoble Valley (France), a Small Apex Ratio Basin

The H/V spectral ratio method based on seismic noise (HVSRN) was used in the Grenoble Basin (France), an Alpine valley characterized by a small apex ratio. The resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1-D theoretical assessment of site responses. Given the abundance of data on the sediments and depth of the basin, the values of the theoretical resonance frequency f_o can be determined quite accurately. However, it has been observed that the effects of basin geometry can disturb f_o measurements using the HVSR method, in particular for a case like the Grenoble Basin, which has a small apex ratio (w/H) and strong suspected 2-D and/or 3-D effects. Interpretation of f_o values in terms of bedrock depth gives rise to estimation errors of about 10% in certain cases, with the most significant errors (>50%) occurring on the edges of the basin, where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated. This study suggests that great care must be taken when using the HVSRN method as an exploration tool, at least in valleys with a small apex ratio.