Improved seismic hazard model with application to probabilistic seismic demand analysis

An improved seismic hazard model for use in performance‐based earthquake engineering is presented. The model is an improved approximation from the so‐called ‘power law’ model, which is linear in log–log space. The mathematics of the model and uncertainty incorporation is briefly discussed. Various means of fitting the approximation to hazard data derived from probabilistic seismic hazard analysis are discussed, including the limitations of the model. Based on these ‘exact’ hazard data for major centres in New Zealand, the parameters for the proposed model are calibrated. To illustrate the significance of the proposed model, a performance‐based assessment is conducted on a typical bridge, via probabilistic seismic demand analysis. The new hazard model is compared to the current power law relationship to illustrate its effects on the risk assessment. The propagation of epistemic uncertainty in the seismic hazard is also considered. To allow further use of the model in conceptual calculations, a semi‐analytical method is proposed to calculate the demand hazard in closed form. For the case study shown, the resulting semi‐analytical closed form solution is shown to be significantly more accurate than the analytical closed‐form solution using the power law hazard model, capturing the ‘exact’ numerical integration solution to within 7% accuracy over the entire range of exceedance rate. Copyright © 2007 John Wiley & Sons, Ltd.     

联结(copula)函数在概率地震危险性分析中的应用

介绍了一种成熟的已广泛应用于金融领域的估计不确定性的方法——copula函数方法, 并推广了n重的Frankrsquo;s copulas; 在实际应用中, 本文采用了俞言祥和美国西部由Boore等人给出的两个衰减模型, 针对其中存在的模型不确定性以及它们之间的相互依赖性, 构造出概率意义上联合的copula分布函数, 并将其应用于实例分析. 结果表明, 对比于传统逻辑树中所用的线性结合方法, copula将两者带来的概率分布写成一个联合概率分布, 能够很好地考虑双方不尽相同的意见. 另外, 由于copula函数可采用各种各样的边际分布函数来获得联合概率分布, 且在金融风险投资评估已有大量的应用, 因此在现代地震危险性评估中将有着广泛的前景.      

Potential rupture surface model and its application on probabilistic seismic hazard analysis

Potential sources are simplified as point sources or linear sources in current probabilistic seismic hazard analysis (PSHA) methods. Focus size of large earthquakes is considerable, and fault rupture attitudes may have great influ-ence upon the seismic hazard of a site which is near the source. Under this circumstance, it is unreasonable to use the simplified potential source models in the PSHA, so a potential rupture surface model is proposed in this paper. Adopting this model, we analyze the seismic hazard near the Chelungpu fault that generated the Chi-Chi (Jiji) earthquake with magnitude 7.6 and the following conclusions are reached. 1 This model is reasonable on the base of focal mechanism, especially for sites near potential earthquakes with large magnitude; 2 The attitudes of poten-tial rupture surfaces have great influence on the results of probabilistic seismic hazard analysis and seismic zoning.     

Regional variation of spectral parameters for seismic design from broadband probabilistic seismic hazard analysis

The characterisation of the seismic hazard input is a critical element of any seismic design code, not only in terms of the absolute levels of ground motion considered but also of the shape of the design spectrum. In the case of Europe, future revisions of the seismic design provisions, both at a national and a pan‐European level, may implement considerable modifications to the existing provisions in light of recent seismic hazard models, such as the 2013 European Seismic Hazard Model. Constraint of the shape of the long‐period design spectrum from seismic hazard estimates on such a scale has not been possible, however, owing to the limited spectral period range of existing ground motion models. Building upon recent developments in ground motion modelling, the 2013 European Seismic Hazard Model is adapted here with a new ground motion logic tree to provide a broadband Probabilistic Seismic Hazard Analysis for rock sites across a spectral period range from 0.05 seconds to 10.0 seconds. The resulting uniform hazard spectra (UHS) are compared against existing results for European and broadband Probabilistic Seismic Hazard Analysis and against a proposed formulation of a generalised design spectrum in which controlling parameters can be optimised to best fit the uniform hazard spectra in order to demonstrate their variability on a European scale. Significant variations in the controlling parameters of the design spectrum are seen both across and within stable and active regions. These trends can help guide recalibrations of the code spectra in future revisions to seismic design codes, particularly for the longer‐period displacement spectrum.     

Sensitivity analysis on the input parameters in probabilistic seismic hazard assessment

A project has been implemented in recent years for assessing seismic hazard in the Italian territory on probabilistic bases, to be used as scientific background for the revision of the current seismic zonation. A consolidated approach was considered for the purpose; seismic hazard was estimated in terms of peak ground acceleration and macroseismic intensity. As the computer code employed allows the user to make specific choices on some input data, some rather unorthodox decisions were taken regarding earthquake catalogue completeness, seismicity rates, boundaries of the seismogenic zones, definition of the maximum magnitude, attenuation relation, etc. The overwhelming amount of geological and seismological data for Italy (just consider, for example, that the earthquake catalogue collects events which occurred over the last ten centuries) permits the operator to make different choices, more or less cautiously. It is quite interesting, then, to evaluate the influence of the specific choices on the final hazard results as a comparison to traditional possibilities. The tests performed clearly indicate the critical choices and quantify their contribution. In particular, we consider thorough comprehension of the space geometry of the earthquake source boundaries and the adequacy of the attenuation relation in modelling the radiation pattern very important.     

Methodological considerations of probabilistic seismic hazard mapping

This paper presents a methodological discussion of several issues involved with the development of maps of seismic hazard. The points made are illustrated with worked examples, using Scotland as an illustrative case. The issues treated are divided under three headings: matters relating to the difference between hazard maps and site studies; matters concerned with the technical issues of mapping, and matters relating to the use to which hazard maps will be put. It is concluded that a hazard map cannot be an all-purpose substitute for site-specific studies, owing to the impracticality of ensuring all-round conservatism in a hazard map, and the lower level of detail (more broad-brush approach) in a regional mapping study. Also, since users of a hazard map are not necessarily going to be engineers, consideration should be given to the provision of maps expressed in parameters other than physical measures of ground motion. Intensity is useful here, since it relates to actual earthquake experience and to damage. One can also move to making maps of generic seismic risk even before one has data on the distribution of exposure and vulnerability. Discussion is made of the issue of testing the validity of hazard maps against real experience, with examples. If a map can be shown to accord with real observations, then it can be treated with greater confidence by users.     

累积绝对速度在核电厂地震危险性分析中的应用研究

指出了运用我国现行的考虑时空非均匀性的地震危险性分析计算方法对核电厂等设计精良的设施进行地震危险性分析时所存在的问题.介绍了累积绝对速度（CAV）的概念,并将其引入到我国现行的考虑时空非均匀性的地震危险性分析计算方法之中,用以排除厂址周围小震对核电厂地震危险性分析的影响,并选取实际工程场点进行了试算.试算结果表明,此方法能明显排除厂址周围小震对地震危险性分析结果的影响.     

Influence of ground-motion correlation on probabilistic assessments of seismic hazard and loss: sensitivity analysis

Recent studies have shown that the proper treatment of ground-motion variability and, particularly, the correlation of ground motion are essential for the estimation of the seismic hazard, damage and loss for distributed portfolios. In this work we compared the effects of variations in the between-earthquake correlation and in the site-to-site correlation on probabilistic estimations of seismic damage and loss for the extended objects (hypothetical portfolio) and critical elements (e.g. bridges) of a network. Taiwan Island has been chosen as a test case for this study because of relatively high seismicity and previous experience in earthquake hazard modelling. The hazard and loss estimations were performed using Monte Carlo approach on the basis of stochastic catalogues and random ground-motion fields. We showed that the influence of correlation on parameters of seismic hazard, characteristics of loss distribution and the probability of damage depend, on one hand, on level of hazard and probability level of interest (return period) and, on the other hand, the relative influence of each type of correlation is not equal.     

Ground-motion characterization for the probabilistic seismic hazard assessment in Turkey

This study describes the methodology implemented to establish the ground-motion logic-tree for national probabilistic seismic hazard map of Turkey for shallow active crustal regions. The presented procedure provides quantitative information to guide the hazard experts while establishing the logic tree to capture the epistemic uncertainty in ground-motion characterization. It uses non-data-driven and data-driven testing methods to identify and rank candidate ground-motion prediction equations (GMPEs) under a specific ground-motion database. The candidate GMPEs are subjected to visual inspection and are classified into center, body and range (CBR) spectral estimates for a proper consideration of epistemic uncertainty. The GMPEs classified into CBR are then used in a suite of seismic hazard sensitivity analysis to establish the most suitable GMPE logic-tree whose spectral estimates are not biased by any one of the GMPEs in the logic-tree structure. The sensitivity analysis considers normalized spectral ordinates and is not manipulated by the spectral amplitudes. The proposed procedure is inherited from the relevant studies of the Earthquake Model of the Middle East (EMME; www.efehr.org:8080/jetspeed/portal/emme.psml) regional seismic hazard project. This paper also highlights the similarities and differences in ground-motion characterization between EMME and our approach.     

双场点地震危险性分析方法及其应用

提出了双场点地震危险性分析方法,用以计算在相同地震构造环境中,相同地震作用下的相邻两个工程场点同时超越其给定地震动参数的概率.该方法是确定系统的危险段落、场点遭受的附加地震危险的有效工具.基于汶川MS8.0地震后大渡河干流及邻近地区的地震环境,以大渡河干流梯级水电站系统为例,确定了大渡河干流梯级水电站各个河段的地震危险性.其中危险性最高的3个河段是:龚嘴—铜街子河段、沙坪—龚嘴河段和大岗山—龙头石河段.     

基于特征地震模型含时间的概率地震危险性分析方法及其应用研究

本文介绍了特征地震的对数正态分布模型、 正态分布模型和布朗过程时间模型, 提出了使用地震破裂面源模型的特征地震含时间的概率地震危险性分析理论和方法. 通过具体算例对不同的特征地震模型进行了比较, 并对特征地震危险性分析方法进行了系统探索. 研究结果表明, 特征地震含时间模型在复发周期早期的地震危险性低于不含时间模型, 而在后期其地震危险性则高于不含时间模型. 特征地震复发周期的对数正态分布模型与布朗过程时间模型计算得出的地震危险性差别不大. 在未到期望复发时间时, 正态分布模型与前两种模型计算的地震危险性差别不大; 而接近期望复发时间及之后时段, 正态分布模型计算的地震危险性则迅速增大.      

余震时空丛集对概率地震危险性分析的影响

本文以东北、华北及川滇地区为例,系统研究了余震时空丛集对概率地震危险性分析的影响.采用基于传染型余震序列模型（ETAS）的蒙特卡罗模拟方法,模拟了包含余震和不包含余震的两套地震序列,然后以模拟地震目录为基础输入,采用基于空间光滑地震活动性模型的地震危险性分析方法计算了两套地震危险性结果——PGA（Peak Ground Acceleration,峰值加速度）,通过分析比较这两套PGA的绝对差值和相对差值来研究余震时空丛集对概率地震危险性分析的影响.研究结果表明余震对50年超越概率10%地震危险性计算结果的影响均值为6%左右,最大可达10%,并且随着超越概率水平的提高,余震影响也越大.弱地震活动区余震对概率地震危险性分析的影响要高于强地震活动区.研究结果还进一步揭示两套PGA结果绝对差值的最大值约为15 cm·s^-2,且出现在高PGA区,这意味着余震对概率地震危险性计算结果不会产生显著影响.因此在地震区划或一般性地震危险性分析中可考虑不用删除余震.

     

改进的确定性地震危险性分析方法及其应用

根据改进的基于振型叠加(mode superposition)技术的地震危险性确定性分析方法,结合区域地震活动性、地质构造和地震波传播特点,通过计算理论地震图途径,分别计算了城市周边各个地震对各个场点所造成的最大影响强度(主要以峰值加速度、速度和位移体现),所确定的参数可为结构抗震设计工作提供客观依据.     

Data needs for probabilistic fault displacement hazard analysis

We present a summary of the methodology for probabilistic fault displacement hazard and discuss the types of data needed for the analysis. The methodology is based on the widely used formulation for probabilistic assessment of ground shaking hazard. We distinguish between principal faulting, ruptures occurring on the fault producing the earthquake, and distributed faulting, ruptures occurring on secondary features around the principal rupture. Data needed for assessments of principal fault displacement hazard are now commonly collected as part of post-earthquake studies and can be compiled and analyzed for this application. Data needed for assessments of distributed fault displacement hazard are collected only sporadically at present.     

Toward a ground-motion logic tree for probabilistic seismic hazard assessment in Europe

The Seismic Hazard Harmonization in Europe (SHARE) project, which began in June 2009, aims at establishing new standards for probabilistic seismic hazard assessment in the Euro-Mediterranean region. In this context, a logic tree for ground-motion prediction in Europe has been constructed. Ground-motion prediction equations (GMPEs) and weights have been determined so that the logic tree captures epistemic uncertainty in ground-motion prediction for six different tectonic regimes in Europe. Here we present the strategy that we adopted to build such a logic tree. This strategy has the particularity of combining two complementary and independent approaches: expert judgment and data testing. A set of six experts was asked to weight pre-selected GMPEs while the ability of these GMPEs to predict available data was evaluated with the method of Scherbaum et al. (Bull Seismol Soc Am 99:3234?C3247, 2009). Results of both approaches were taken into account to commonly select the smallest set of GMPEs to capture the uncertainty in ground-motion prediction in Europe. For stable continental regions, two models, both from eastern North America, have been selected for shields, and three GMPEs from active shallow crustal regions have been added for continental crust. For subduction zones, four models, all non-European, have been chosen. Finally, for active shallow crustal regions, we selected four models, each of them from a different host region but only two of them were kept for long periods. In most cases, a common agreement has been also reached for the weights. In case of divergence, a sensitivity analysis of the weights on the seismic hazard has been conducted, showing that once the GMPEs have been selected, the associated set of weights has a smaller influence on the hazard.     

Copula joint function and its application in probability seismic hazard analysis

A mature mathematical technique called copula joint function is introduced in this paper, which is commonly used in the financial risk analysis to estimate uncertainty. The joint function is generalized to the n-dimensional Frank’s copula. In addition, we adopt two attenuation models proposed by YU and Boore et al, respectively, and construct a two-dimensional copula joint probabilistic function as an example to illustrate the uncertainty treatment at low probability. The results show that copula joint func...     

Interrelation among strong earthquakes and its application in seismic hazard analysis

The intterrelation among strong earthquakes and its application are emphatically studied in this paper. Taking North China seismic region as study area, we have investigated how a great earthquake influence other strong earthqukaes in neighbouring area? Does there exist earthqukae immunity phenomenon? If it exists, what distributional pattern did it has in space-time domain? The results show that occurrence of earthquakes withM⩾7 has cetain immunity phenomenon to earthquakes withM⩾6 in North China. Among others, the immunity area of earthquakes withM=8 is much larger than that ofM=7. For earthquakes withM⩾8, the immunity area to the earthquakes ofM=7 is larger than toM=6. Based on the above analysis, using some statistical methods, we gave the variational regularity of seismic immunity factor with space and time, and explored its concrete application in seismic hazard analysis. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 339–346, 1993.     

A Bayesian methodology to update the probabilistic seismic hazard assessment

This paper presents a Bayesian methodology for updating the seismic hazard curves. The methodology is based on the comparison of predictive exceedance rates of a fixed acceleration level (given by the seismic hazard curves) and the observed exceedance rates in some selected sites. The application of the methodology needs, firstly, the definition of a prior probabilistic seismic hazard assessment based in a logic tree. Each main branch corresponds to a probabilistic model of calculus of seismic hazard. The method considers that, initially (or a priori), the weights of all branches of the logic tree are equivalent. Secondly, the method needs to compile the observations in the region. They are introduced in a database containing the recorded acceleration data (during the instrumental period). Nevertheless, the instrumental period in stable zones (as France) shows only very low acceleration levels recorded during a short observation period. Then, a method to enlarge the REX (number of observations) is presented taking into account the historical data and defining “synthetic” accelerations in the sites of observation. The synthetic REX allows to expand the period of observation and to increase the acceleration thresholds used in the Bayesian updating process. The application of the Bayesian approach leads to a new and more objective definition of the weights of each branch of the logic tree and, therefore, to new seismic hazard curves (mean and centiles). The Bayesian approach doesn’t change the probabilistic models (seismic hazard curves). It only modifies the weights of each branch of the logic tree.     

Site specific probabilistic seismic hazard analysis at Dubai Creek on the west coast of UAE

A probabilistic seismic hazard analysis (PSHA) was conducted to establish the hazard spectra for a site located at Dubai Creek on the west coast of the United Arab Emirates (UAE). The PSHA considered all the seismogenic sources that affect the site, including plate boundaries such as the Makran subduction zone, the Zagros fold-thrust region and the transition fault system between them; and local crustal faults in UAE. PSHA indicated that local faults dominate the hazard. The peak ground acceleration (PGA) for the 475-year return period spectrum is 0.17 g and 0.33 g for the 2,475-year return period spectrum. The hazard spectra are then employed to establish rock ground motions using the spectral matching technique.