来自网上的动态地震图

现在在因特网上可以得到动态地震数据。全球地震台网 ( GSN)的两个数据采集中心已开发了近实时的服务器 ,使我们可直接得到来自 GSN台站的数据。两种类型的数据服务器都可由他们的缩写知道 :L ISS——动态因特网地震服务器 ,是由美国地质调查局阿尔伯克基地震实验室 ( ASL)开发的 ;NRTS—近实时系统 ,是由加州大学圣地亚哥分校开发的。虽然这篇文章着重于 L ISS,但 NRTS有着相似的功能。地震台网阿尔伯克基地震实验室现在运行着大约75个 GSN台站和加州大学圣地亚哥分校( UCSD)加速度检波器国际部署 ( IDA)工程小组大约 3 3个 …     

运用理论格林函数模拟新疆阿克陶6.7级地震强地面运动

运用QSGRN/QSCMP理论地震图计算与合成方法,根据震源机制解设定断层几何参数,模拟了2016年11月25日阿克陶6.7级地震周边区域加速度记录,经场地条件校正绘制了地震峰值加速度分布图。通过对2个强震台观测波形数据与模拟加速度波形数据在时间域和频率域进行对比分析,验证了两者振幅数量级相当、频谱特征一致性较强。同时,提取了实际调查点坐标所对应的模拟峰值加速度,并与实际调查点烈度进行对比,发现两者具有较好的对应关系。文中尝试提供1种震后快速产出峰值加速度分布情况的方法,为监测台站稀少、地形复杂、难以快速开展现场地震灾害调查的地区提供地震影响场范围估计,为地震灾害快速评估与应急决策等工作提供辅助资料。     

Hilbert-Huang变换中的一种端点处理方法

在HHT方法中,边界处理问题是经验模态分解过程中的核心问题,处理不好会引起数据端部的“飞翼”,进而“污染”整个数据,使分解的固有模态函数失效。解决此问题有两种方法:在数据两端加子波和在数据两端各添加两个极值点。对仿真信号的处理证明这两种方法都是有效的,而后一种方法效果更好。利用后一种方法,对1996年丽江7.0级地震的一条强余震加速度记录进行了分析,加深了对强地震动特性的了解。     

北天山最大水平加速度与震级和震中距的关系

为了评定地震危险性，在土层的最大加速度曲线中，研究加速度振幅衰减函数的意义重大，这对于近场尤其如此。在北天山地区，积累的强地面运动资料（共２６８个记录）大部分是远场的，仅对于一个地震—１９９０年震级为６．３的巴索伦斯克（）地震一有两个台站获得到近场记录。因此，仅仅根据部分资料要想得到最大加速度与震级、震中距的经验关系那是不可能的。对世界强运动有代表性的资料进行总结后得到某些关系，在北天山地区研究了利用这些关系的可能性。由大量这种形式的关系式中选出了阿布季达耶夫（）（１９７９）、卡姆布别尔（）（１９８１）和福库史玛（）塔那卡（）（１９９０）的关系式，研究了数据值Ｉｇ（Ａｐ／ＡＨ）随震级和震中距的分布。此处ＡＰ是根据这些关系式中的每一个计算出的加速度值；ＡＨ是在水平分量上观测到的最大振幅。实验观测资料与由卡姆布别尔和福库史玛，塔那卡所得到的修订了的全球关系式显出令人满意的相符。与阿布季达夫相比，当Ｍ≥５．５时是可以使用的。在这种情况下，作为在其它区域所得到的关系式之使用标准，应用时具备两个条件：（１）在所有震级和震中距的取值域中，数值ｌｇ（ＡＰ／ＡＨ）的分布由中值附近趋向零；（２）均方差值不超过０．４０个对数单     

考虑场地特征的强震地面运动参数的统计分析

本文利用笔者所收集的133条国内外重要强震加速度记录进行统计回归分析,得到反映强震地面运动最大峰值加速度、峰值速度、峰值位移、有效峰值加速度及持续时间衰减规律的回归公式。这些记录中所含七级以上大震、震中距小于20公里的近场记录和基岩上的记录较过去许多研究者用以进行统计的记录要多。统计样本中各类数据的分布比较合理。采用场地等效固有周期(以下简称场地固有周期)取代常用的场地分类形式进行统计,在一定程度上克服了场地分类标准不明确的缺点。场地固有周期依据地质钻探资料计算,从而能比较准确地反映与场地特征有关的强震地而运动衰减规律,为实际工程应用提供可靠的经验公式。     

福建地区中小地震地震动峰值衰减规律研究

基于福建省地震监测台网7个基岩台站1999——2007年获得的94次地震(ML=2.8——4.9,Delta;=13——462 km)的1974条宽频带速度记录, 利用实时仿真方法得到了相应的加速度记录, 进而利用不同的模型对数据进行回归分析, 获得了福建地区基岩场地中小地震峰值加速度和峰值速度的衰减关系, 并用2007年8月29日永春M4.6地震对该规律进行验证. 本文方法为速度资料研究地震动衰减规律提供了新的思路.      

利用近场地震加速度记录测定近震震级ML的研究

本文对如何利用强震加速度记录测定近震震级ＭＬ的问题进行了研究，指出了在我国所使用的原始量规函数存在着系统偏差，并用回归现有观测资料的方法修正了这种系统偏差。用修正后的量规函数，利用近场加速度记录计算的ＭＬ值同微震台网所测定的值符合得较好，说明本文所提出的方法是可行的。     

面向地震烈度仪的现地地震动预测模型的构建与验证

利用初期P波预警参数构建现地地震动预测模型,使其在达到设定阈值时快速发出报警信息,是现地地震预警系统面临的一个关键问题,直接关系到发布信息的准确性和及时性。针对地震烈度仪基于微机电系统传感器记录到的数据质量较差,通过两次积分获取的位移存在较大偏差,会引起更多的误报和漏报,本文采用不同阶数（1—4阶）的巴特沃斯滤波器,分别构建了基于P波3 s和全P波段数据的位移幅值PD、速度幅值PV和加速度幅值PA与地震动峰值速度PGV和峰值加速度PGA的现地地震动预测模型,然后利用收集到的川滇示范预警网地震事件记录进行验证。结果表明,对于地震烈度仪微机电系统传感器的记录,采用1阶巴特沃斯滤波器处理、基于全P波段波形拟合获取到的PV与PGV的相关性和PA与PGA的相关性为两种最优现地地震动预测模型。具体应用时,应同时利用两种或两种以上的统计关系进行现地地震动预测,并将实际地震动观测值作为额外的判定条件,以降低误报率和漏报率。      

1984年5月21日南黄海地震的震源参数——用IDA记录测定浅震震源参数

本文讨论了利用国际部署加速度仪台网(IDA)的超长周期瑞雷波记录,反演震源参数的有关理论和方法.对于震源深度大于30km的地震,地震矩张量的五个元素都可以测定;对于浅源(h30km)地震,其中两个元素变为无解[1,2,3].本文以1984年5月21日南黄海浅源地震为例,研究了在浅震难题的情况下,如何更多地提取震源信息的问题,测定了主震的断层机制为:走向北35西,倾角52,滑动方向54,地震矩为1.21018Nm,压应力主轴方向为北74.4东,是一个走向北北西的左旋逆断层.本文还阐述了分布源模型问题。结果表明,采用分布源与采用点源模型对南黄海这种中强地震反演结果的影响不大.分析了震源有限性问题,提出了进行修正的一种明确表达式.      

用人工地震波研究三峡地区地面地震动衰减特征

利用长江三峡工程坝区及外围深部构造的人工地震波记录资料,进行了相对速度幅值、速度反应谱和加速度反应谱衰减特征分析,同时利用历史地震资料经转换命同的地震动衰减规律进行对比,反映出由人工地震记录地震动参数衰减特征与由历史资料转换确定的地震动衰减特征是有差异的,在不同地质条件的局部地区,这一差异更为明显,这些结果中为缺乏强震记录的地区的地震动估计提供参考。     

Prediction of the median IDA curve by employing a limited number of ground motion records

A methodology has been proposed which can be used to reduce the number of ground motion records needed for the reliable prediction of the median seismic response of structures by means of incremental dynamic analysis (IDA). This methodology is presently limited to predictions of the median IDA curve only. The reduction in the number of ground motion records needed to predict the median IDA curve is achieved by introducing a precedence list of ground motion records. The determination of such a list is an optimization problem, which is solved in the paper by means of (1) a genetic algorithm and (2) a proposed simple procedure. The seismic response of a simple, computationally non‐demanding structural model has been used as input data for the optimization problem. The presented example is a three‐storey‐reinforced concrete building, subjected to two sets of ground motion records, one a free‐field set and the other a near‐field set. It is shown that the median IDA curves can be predicted with acceptable accuracy by employing only four ground motion records instead of the 24 or 30 records, which are the total number of ground motion records for the free‐field and near‐field sets, respectively. Copyright © 2007 John Wiley & Sons, Ltd.     

Bias assessment in Incremental Dynamic Analysis due to record scaling

Incremental Dynamic Analysis (IDA) involves a series of nonlinear response history analyses with a suite of incrementally scaled ground motion records. Although IDA is perhaps the most comprehensive seismic performance assessment method, it receives criticism because several ground motion records are scaled up until the structure collapses. The scaling practice often results to unrealistic multipliers, thus modifying the amplitude of the ground motion and introducing bias on the structural performance estimation. Record scaling is a common practice in earthquake engineering due to the lack of natural records corresponding to large magnitudes and/or small distances from the fault rupture location. In this work we use a large number of ground motion records to compare the predictions of IDA with that of unscaled ground motions and we propose a new methodology in order to quantify the bias introduced in IDA. Apart from natural records, we have conducted broadband ground motion simulations for rupture scenarios of weak, medium and large magnitude events in order to expand our record database. The investigation is performed on a series of inelastic single-degree-of-freedom systems and on two multistory steel moment frame buildings. The results pinpoint both qualitatively and quantitatively, for the full range of limit-states, the bias that IDA introduces on the structural performance estimation.     

Incremental dynamic analysis with consideration of modeling uncertainties

Incremental dynamic analysis (IDA) has been extended by introducing a set of structural models in addition to the set of ground motion records which is employed in IDA analysis in order to capture record‐to‐record variability. The set of structural models reflects epistemic (modeling) uncertainties, and is determined by utilizing the latin hypercube sampling (LHS) method. The effects of both aleatory and epistemic uncertainty on seismic response parameters are therefore considered in extended IDA analysis. The proposed method has been applied to an example of the four‐storey‐reinforced concrete frame, for which pseudo‐dynamic tests were performed at the ELSA Laboratory, Ispra. The influence of epistemic uncertainty on the seismic response parameters is presented in terms of summarized IDA curves and dispersion measures. The results of extended IDA analysis are compared with the results of IDA analysis, and the sensitivity of the seismic response parameters to the input random variable using the LHS method is discussed. It is shown that epistemic uncertainty does not have significant influence on the seismic response parameters in the range far from collapse, but could have a significant influence on collapse capacity. Copyright © 2008 John Wiley & Sons, Ltd.     

Seismic reliability assessment of a steel moment-resisting frame with two different ductility levels using a cloud analysis approach

A cloud method for generating percentile engineering demand parameter versus intensity measure(EDP-IM) curves of a structure subjected to a set of synthetic ground motions is presented. To this end, an ensemble of synthetic ground motions based on available real ones is generated. This is done by using attenuation relationships, duration and suitable Gutenberg-Richter relations attributed to the considered seismic hazard at a given site by estimating a suitable distribution of magnitude and site to source distance. The study aims to clarify the significance of the duration and frequency content on the seismic performance of structures, which were not considered in developing percentile incremental dynamic analysis(IDA) curves. The collapse probabilities of two steel moment-resisting frames with different ductility levels generated by IDA and the proposed cloud method are compared at different intensity levels. When compared with conventional IDA, the suggested cloud analysis(SCA) methodology with the same run number of dynamic analyses was able to develop response hazard curves that were more consistent with site-specific seismic hazards. Eliminating the need to find many real records by generating synthetic records consistent with site-specific seismic hazards from a few available recorded ground motions is another advantage of using this scheme over the IDA method..     

Developing efficient scalar and vector intensity measures for IDA capacity estimation by incorporating elastic spectral shape information

Scalar and vector intensity measures are developed for the efficient estimation of limit‐state capacities through incremental dynamic analysis (IDA) by exploiting the elastic spectral shape of individual records. IDA is a powerful analysis method that involves subjecting a structural model to several ground motion records, each scaled to multiple levels of intensity (measured by the intensity measure or IM), thus producing curves of structural response parameterized by the IM on top of which limit‐states can be defined and corresponding capacities can be calculated. When traditional IMs are used, such as the peak ground acceleration or the first‐mode spectral acceleration, the IM‐values of the capacities can display large record‐to‐record variability, forcing the use of many records to achieve reliable results. By using single optimal spectral values as well as vectors and scalar combinations of them on three multistorey buildings significant dispersion reductions are realized. Furthermore, IDA is extended to vector IMs, resulting in intricate fractile IDA surfaces. The results reveal the most influential spectral regions/periods for each limit‐state and building, illustrating the evolution of such periods as the seismic intensity and the structural response increase towards global collapse. The ordinates of the elastic spectrum and the spectral shape of each individual record are found to significantly influence the seismic performance and they are shown to provide promising candidates for highly efficient IMs. Copyright © 2005 John Wiley & Sons, Ltd.     

Cloud to IDA: Efficient fragility assessment with limited scaling

Incremental dynamic analysis (IDA) leads to curves expressed in terms of structural response versus intensity, commonly known as the IDA curves. It is known that implementation of IDA usually involves significant computational effort and most often significant scaling of the original records to various intensity levels. Employing as the performance variable the critical demand to capacity ratio (DCR) throughout the structure, which is equal to unity at the onset of the limit state, facilitates the identification of the intensity values at the onset of a desired limit state and hence the implementation of the IDA procedure. Employing the structural response to un‐scaled records and the corresponding regression‐based response predictions (a.k.a., the “Cloud Analysis”) helps in identifying the range of intensity values corresponding to demand to capacity ratio values in the vicinity of unity. The Cloud to IDA procedure for structural fragility assessment is proposed on the premise of exploiting the Cloud Analysis results to obtain the IDA curves both with minimum number of analyses and minimum amount of scaling. The transverse frame of a shear‐critical 7‐story older RC building in Van Nuys, CA, which is modeled in Opensees with fiber‐section considering the flexural‐shear‐axial interactions and the bar slip, is employed as a case study. It is demonstrated, by comparing the results to IDA and other state of the art non‐linear dynamic procedures based on no scaling or spectral‐shape‐compatible scaling, that the Cloud to IDA procedure leads to reliable results in terms of structural fragility and risk for the prescribed limit state.     

Incremental dynamic analysis of concrete gravity dams including base and lift joints

The growth in computer processing power has made it possible to use time-consuming analysis methods such as incremental dynamic analysis(IDA) with higher accuracy in less time.In an IDA study,a series of earthquake records are applied to a structure at successively increasing intensity levels,which causes the structure to shift from the elastic state into the inelastic state and finally into collapse.In this way,the limit-states and capacity of a structure can be determined.In the present research,the IDA of a concrete gravity dam considering a nonlinear concrete behavior,and sliding planes within the dam body and at the dam-foundation interface,is performed.The influence of the friction angle and lift joint slope on the response parameters are investigated and the various limit-states of the dam are recognized.It is observed that by introducing a lift joint,the tensile damage can be avoided for the dam structure.The lift joint sliding is essentially independent of the base joint friction angle and the upper ligament over the inclined lift joint slides into the upstream direction in strong earthquakes.     

Equating incremental dynamic analysis with static nonlinear analysis at near-field excitation

In an incremental dynamic analysis(IDA) using a set of ground motion records,nonlinear time history analysis needs to be performed on structures.It is well recognized that IDA calls for high computational efforts and the results are highly sensitive to selected ground motions.As a result,alternative static methods are needed.This study aims to introduce a new double-stage(N1- N2) static method to estimate capacity curves of MR frames.The technique is regulated to resemble IDA results with specific emphasis on near-field ground motions.Using an ensemble of 56 near-field earthquake records,required ID As have been carried out for SAC-Los Angeles 3-,9- and 20-story buildings and an additional 15-story building.The results of the proposed static method are compared with those from IDA,displacement-based adaptive procedure(DAP),and multimodal procedure(MMP).The results indicate that in addition to enhanced accuracy,very little time is required in the case of N1-N2 method.Thus,for the 3-story structure,the time required is less than 1 minute.The proposed N1-N2 method shows the best accuracy in terms of lateral mechanisms for the 15-story frame while for the other cases,the first mode load pattern leads to the best accuracy.     

A negative search for an ultra-slow component to the source of the Yunnan earthquakes of May 29, 1976

Following Nagamune's suggestion of a giant, but very slow, component to the source of the Yunnan earthquakes of May 29, 1976, a systematic study of the ultra-low frequency content of a number of tiltmeter, strainmeter, and IDA records of the events is conducted. First, Nagamune's hypothesis is quantified, and it is found that it would require a moment in the range 10²⁹–10³⁰ dyn-cm. Such a large moment would have important consequences for our understanding of stress release in the plates, but is incompatible with the extent of the aftershock zone, and with observations on other instruments: specifically, only one IDA record shows a time-domain oscillation which may be related to the proposed source. In the Fourier domain, however, a spectral analysis fails to identify any of the Earth's modes in any of the available records, including the one originally used by Nagamune. It must therefore be concluded that the apparent signal present in a few records is due to noise—probably of instrumental origin—rather than to an ultra-low-frequency component of the seismic source.     

Prediction of seismic collapse risk of steel moment frame mid-rise structures by meta-heuristic algorithms

Different performance levels may be obtained for sideway collapse evaluation of steel moment frames depending on the evaluation procedure used to handle uncertainties. In this article, the process of representing modelling uncertainties, record to record (RTR) variations and cognitive uncertainties for moment resisting steel frames of various heights is discussed in detail. RTR uncertainty is used by incremental dynamic analysis (IDA), modelling uncertainties are considered through backbone curves and hysteresis loops of component, and cognitive uncertainty is presented in three levels of material quality. IDA is used to evaluate RTR uncertainty based on strong ground motion records selected by the k-means algorithm, which is favoured over Monte Carlo selection due to its time saving appeal. Analytical equations of the Response Surface Method are obtained through IDA results by the Cuckoo algorithm, which predicts the mean and standard deviation of the collapse fragility curve. The Takagi-Sugeno-Kang model is used to represent material quality based on the response surface coefficients. Finally, collapse fragility curves with the various sources of uncertainties mentioned are derived through a large number of material quality values and meta variables inferred by the Takagi-Sugeno-Kang fuzzy model based on response surface method coefficients. It is concluded that a better risk management strategy in countries where material quality control is weak, is to account for cognitive uncertainties in fragility curves and the mean annual frequency.