基于强震台网的我国沿海海啸走时预警

经济快速发展的中国沿海地区,面临着潜在海啸袭击危险。海啸传播走时分析是海啸预警系统的重要组成部分。本文基于强震台网提供的地震要素,从理论上讨论海啸预警时间计算方法。在球坐标系下,建立了远洋海啸传播模型,采用差分技术,实现远洋海啸传播数值模拟,首次针对我国主要城市进行了海啸走时计算,分析了我国沿海走时特点,指出了未来发生在太平洋的远洋海啸对我国的长江三角洲会有较大影响。本文计算海啸走时方法可以为我国建设的新一代基于数值海啸预警系统提供技术支持。     

我国强地震动记录特征综述

本文概述了我国强地震动台网的发展历程, 总结了唐山地震的强地震动记录特征和2007年以来我国数字台网获取的强地震动记录特征, 重点分析了近年来发生的几次典型破坏性地震的强地震动记录特征． 结果表明: 我国近场地震动记录体现了近场的方向性效应、 上/下盘效应、 速度脉冲、 局部场地效应等多样性特征, 可以进一步服务于地震工程领域的科学研究与工程应用．      

地震动参数衰减规律的研究

对收集到的近两万条美国西部的强震记录进行了分析整理，选用了108个台站共324条基岩强地震动记录，对建议的地震动参数衰减模型进行了统计，该地震动参数衰减模型中考虑了区域介质品质因子，试图通过不同地区介质品质因子的差异规律来实现地震动参数衰减特性的相互转换。这对缺乏强震记录资料地区的地震动参数估计将带来极大的方便。     

强震地面运动的超随机特性研究

简述了几种常用的地震动平稳随机模型，这几种地震动平稳随机模型的功率谱是一组光滑的函数，相应的自相关函数基本上是指数衰减的振荡函数，且很快衰减到零；但是真实地震动的归一化自相关函数则有一较显著的随机噪声项，这个随机噪声的幅值为0．15左右，这就是本文中所说的超随机特性。目前常用的地震动平稳随机模型没有考虑这个随机噪声项及其对结构反应的影响。本文将真实地震动的自相关函数分解为一确定性函数和一随机噪声的叠加，并对自相关函数中的噪声部分进行了分析，得出两条重要性质。本文的研究结果表明地震动加速度时程的平方和(SS)比峰值加速度(PGA)更好地量度了地震地面运动强度。由于归一化自相关函数的随机噪声部分所对应的功率谱的随机波动成分对频率的积分为零，即归一化自相关函数的噪声部分对地震动总功率或平方和的贡献为零，因此自相关函数的随机噪声项对地震动的幅值影响不大，但自相关函数的随机噪声项明显改变了地震动功率谱在频域上的分布特征，因此会对结构反应产生一定的影响。由于篇幅所限详细内容将在下一篇文章中作进一步探讨。     

竖向地震动特征研究

本文以国内外数十次地震(ML≥5)的近场自由地表加速度记录为基础数据,进行近场加速度峰值比的统计分析,并着重对1999年台湾集集地震竖向地震动反应谱特征进行研究。统计结果表明,竖向与水平向(V／H)加速度峰值比与震源距相关,随震源距增加,比值降低;竖向反应谱及竖向与水平向加速度反应谱比是周期的函数、并与场地条件及震源距相关。     

Site effects on strong ground motion

A review of some of the available methods to study the effects of site conditions on strong ground motion is presented. The need of unified treatment of source, path and side effects in the assessment of seismic risk is pointed out.     

A nonparametric characterization of vertical ground motion effects

Design guidelines have traditionally oversimplified the vertical ground motion effects by defining a constant vertical‐to‐horizontal response spectral ratio (V/H). With the recognition that such practice is not always conservative, recent studies have proposed improvements to the representation of vertical seismic effects in design codes, based on empirical ground motion relations. Conventional empirical modeling requires selecting the functional form of the predictive model. Because of the complicated nature of ground motions, identification of the underlying function is a challenge. A related drawback to this approach is its high susceptibility to overfitting, especially with today's highly complex models. To address these issues, this paper proposes a nonparametric approach to characterize the vertical seismic effects. Using support vector machines, the V/H ratio is determined without an assumed functional form. The accuracy of the model is measured by adopting an epsilon‐insensitive residual function with a regularization term added to prevent overfitting. An example application using ground motion records from strike‐slip and normal faulting earthquakes is presented, and the results are compared with a current empirical model, for different magnitude, distance, and local soil conditions. The median V/H estimates from the two models are shown to be in good general agreement. The standard deviation estimates from the proposed model are consistently larger than the estimates from the empirical model. The results from this study show that the proposed method is a viable alternative and offers the opportunity to characterize vertical seismic effects without an assumed functional form. Copyright © 2011 John Wiley & Sons, Ltd.     

近断层地震动的基本特征

本文对近断层地震动的基本特征作了详细分析,这些基本特征主要包括近断层强地震动的集中性、地表破裂、地面永久变形、破裂的方向性效应、近断层速度大脉冲和上盘效应。这些特征虽然在一次地震中不一定同时出现,但它们是已经被强震观测资料和数值模拟证实了的,在模拟和预测近断层地震动时,必须充分考虑这些特点,合理的近断层地震动模拟或预测模型和方法应当在结果中再现这些特点。     

基于场地效应的地震动特性研究

为了研究强地震作用下,场地类别对于地震动幅频特性的影响,本文统计了3 579条日本地震动的时程,并针对场地类别的不同,分别从基岩和土层的峰值加速度幅值特性角度,以及从标准化反应谱和平均加速度反应谱等频谱特性的角度研究其幅频衰减特性,最后给出了各类场地峰值加速度衰减曲线。结果表明,土层对于地震动幅值和频谱的放大作用会随着场地类别的变软而增加,并且场地越软,远场的长周期特性越明显。利用平均加速度反应谱可以有效地反映频谱中的长周期成分。     

3-D physical model in strong ground motion numerical simulation： A case study of Kunming basin

Seismic hazard assessment based on urban active faults can provide scientific bases for city planning and projectconstruction,while numerical simulation of strong ground motion is an important method for seismic hazard pre-diction and assessment.A 3-D physical model in conformity with real strata configuration of(mainly)the Quater-nary is a prerequisite to ensure the reliability of the simulation results.In this paper,we give a detailed account ofthe technical scheme and process for creating a 3-D physical model in Kunming basin.The data used are synthe-sized from seismogeological data,borehole data,topographic data,digital elevation mode(DEM)data,seismicexploration results and wave velocity measurements.Stratigraphic division is based mainly on shear wave velocity,with strata sequence taken into consideration.The model construction is finally accomplished with ArcGIS andmany relevant programming techniques via layer-by-layer stacking(in depth direction)of the adjacent mediuminterfaces(meshes).Meanwhile,a database of 3-D physical models is set up,which provides model data and pa-rameters for strong ground motion simulation.Some processing methods and significant issues are also addressedin the paper in accordance with different types of exploration and experimental data.     

唐山响堂三维场地影响观测台阵

１９９４年７月中国地震局工程力学研究所在唐山余震区响堂镇建成了我国第一个三维场地影响观测台阵。该台阵目前有四个测点,分别布设在基岩地表、土层地表、地下１７ｍ和地下３２ｍ处。它安装了分辨率为１６位的井下数字观测系统,主机和从机同步运行,系统时钟采用Ｏｍｅｇａ导航信号自动校对（精度１ｍｓ）,地震数据采用固态方式（ＣＭＯＳ）存储,每个测点均布设一组 量力平衡式加速度计。该台阵自投入运行至１９９７年１２月     

Earthquake ground motion characteristics and seismic energy dissipation

The sensitivity of seismic energy dissipation to ground motion and system characteristics is assessed. It is found that peak ground acceleration, peak ground velocity to acceleration (V/A), dominant period of ground excitation and effective response duration are closely correlated with the energy dissipated by a SDOF system. Ductility ratio and damping ratio have no significant influence on the energy dissipation. An energy dissipation index is proposed for measuring the damage potential of earthquake ground motion records which includes the effects of basic excitation and response characteristics contributing to the seismic energy dissipation. The proposed index is compared with several intensity measures for the set of 94 ground motion records considered in the study.     

A study on amplification response of soil ground motion in Shanghai using strong motion records

Introduction A good deal of attention was paid to the amplification response of soil layers under the earthquake waves,especially by the engineering seismologists.     

A study on the duration and amplitude characteristics of earthquake ground motions

The duration, total power, rms amplitude, and peak ground acceleration (PGA) are examined using the data from the KiK-net digital borehole accelerograph arrays in Japan during three large earthquakes. We investigate correlations between the duration, PGA on the surface and hypocentral distance, instrumental seismic intensity, and the local site conditions. Also considered in this paper, are correlation between the duration and PGA. This present study suggests that PGA is inversely proportional to the duration.Comparing the duration, total power, rms amplitude, and PGA on the surface with those at the bottom of borehole, the duration and maximum amplitude characteristics of earthquake ground motions are investigated with emphasis on site amplification due to the local site conditions. The difference of amplification factors is not only site-dependent but also event-dependent. The comparison of the site amplification factors and the average shear-wave velocity in the upper 30-m showed a good agreement.This paper indicated that the duration and amplitude characteristics suffer a reciprocal effect due to the local site conditions and the site dependency of maximum amplitude PGA is greater than that of the duration. In view of the results, the duration is not less important than the maximum amplitude and frequency content in earthquake engineering. Moreover, this study provided meaningful information of input motion available to earthquake-resistant design.     

Numerical study of characteristics of underground blast induced surface ground motion and their effect on above-ground structures. Part I. Ground motion characteristics

Current codes of practice in assessing the blast ground motion effect on structures are mainly based on the ground peak particle velocity (PPV) or PPV and the principal frequency (PF) of the ground motion. PPV and PF of ground motion from underground explosions are usually estimated by empirical formulae derived from field blast tests. Not many empirical formulae for PF, but many empirical formulae for PPV are available in the literature. They were obtained from recorded data either on ground surface or in the free field (inside the geological medium). Owing to the effect of surface reflection, blast motions on ground surface and in the free field are very different. But not many publications in the open literature discuss the differences of blast motions on ground surface and in the free field. Moreover, very few publications discuss the blast ground motion spatial variation characteristics. As ground motion directly affects structural responses, it is very important to study its characteristics in order to more reliably assess its effects on structures. In this paper, a validated numerical model is used to simulate stress wave at a granite site owing to explosion in an underground chamber. Using the simulated stress wave, the relations such as PPV and PF attenuation as well as spatial variation of motions on ground surface and in the free field are derived. Discussions on the differences of the characteristics of surface and free field motions are made. Results presented in this paper can be used in a more detailed assessment of ground motion effect on structures.     

特殊长周期地震动的参数特征研究

近断层脉冲型地震动和远场软土层场地类谐和地震动是两类特殊的长周期地震动,当前的规范均很少对这两类地震作用进行具体的规定。研究了近断层脉冲型和远场类谐和地震动的幅值、幅值比（V／A,D／V）、傅里叶幅值谱和反应谱的差别,分析了相位角和作用循环周期数对简单脉冲的影响,并用于解释两类特殊地震动的工程特征。以集集地震动为数据基础,分析了两类长周期地震动的傅里叶谱和反应谱特征;将平均加速度和位移规准反应谱分别与规范设计谱进行了比较。建议设计谱在长周期段考虑近断层作用和软土场地面波效应的影响。     

A numerical approach for modeling near-fault ground motion and its application in the 1994 Northridge earthquake

An approach for simulating near-fault ground motion was presented by combining the finite fault model with a numerical algorithm, named investigated lump method presented in this paper for wave propagation. The investigated lumps are constructed from the auxiliary quadrilateral grids. The dynamic equilibrium equations of a typical investigated lump have been derived and obtained by integrating the stresses along the contour of the investigated lump. The stresses are calculated using the constitutive relations and the interpolation techniques. The investigated lump method is then implemented using the equilibrium equations of investigated lumps and the calculations of stresses alternately in time domain. The stability criterion of the algorithm has been given. Comparisons with the discrete wave-number method solutions for predicting the ground motions at the Pacoima Dam during the San Fernando earthquake show the validity of the method presented in this paper for simulating near-field ground motions. A finite fault source model has been implemented in the algorithm here. The source parameters given by Wald et al. (1996) [18] are applied to synthesize the ground motions at three stations during the 1994 Northridge earthquake. The simulating results qualitatively match to the corresponding ground motion records. The studies demonstrated that the approach presented in this paper is an effective tool for the numerical simulation of near-fault ground motion.     

Simulation of near source ground motion and its characteristics

It is fact that the severe ground motions of shear waves have a strong effect on the dynamic behavior of buildings and civil structures. We simulate near source strong motions of a pure shear wave and synthesize small motions, using the parameters based on the recorded accelerograms at the site that is regarded as a base rock in the Osaka basin, Japan. By making use of a stochastic technique, we can easily introduce higher frequency contents in the motions and apply the technique to the synthesis of small waves regarding as a green function. We also introduce to the analysis the useful relationships among the time duration T_d, the seismic moment M₀, the corner frequency f_c and the high cutoff frequency f_max which were regressed by a simple representation scheme. Considering two active faults that may affect severe damage on buildings and civil structures, we try to predict strong ground motions in Osaka basin and show the characteristics of them.