核电厂地震安全性评价衰减关系影响分析

地震危险性分析中的不确定性处理和表征,一直是核电厂厂址地震安全性评价中倍受关注的重要问题,尤其是日本福岛核事故后,无论是确定核电厂厂址的设计基准地震动,还是进行核电厂地震风险评价,都更加重视地震危险性分析中的不确定性.本文通过理论分析重点说明了衰减关系的不确定性,包括标准差和截断水平对核电厂地震安全性评价的影响,并在此基础上,通过算例和讨论说明了概率性方法截断水平的选取问题,探讨了现行确定性方法和概率性方法在截断水平选取上的差异.分析计算结果表明,在地震活动较弱的区域,概率性方法截断水平为3,确定性方法截断水平为0的现行做法是恰当的.但是,对于发震构造大震复发间隔较小的区域,为了使二者在超越概率方面协调,恰当提高确定性方法的截断水平更为合理.     

考虑时空非均匀性的地震危险性分析简易算法

本文以我国第三代烈度区划工作所采用的地震危险性分析思路为基础,沿袭断层破裂模型中分条积分的简易性,提出了考虑地震活动时空非均匀性的地震危险性分析简易算法,使第三代烈度区划的地震危险性分析思路在地震烈度复核和地震小区划工作中得到更好的推广和应用。     

核设施地震危险性分析方法研究

福岛核事故揭示了外部自然灾害引发严重核事故的可能性,为核工程界敲响了警钟。因此,对我国运行和在建核电厂址逐步开展了抗震裕度评价(SMA)或地震概率安全评价(SPSA)工作。本文针对地震危险性分析在核工程应用中存在的问题,从设计基准地震动的确定、核电厂地震概率安全评价、超设计基准地震动安全分析3个方面进行了研究。设计基准地震动确定方面,目前存在的主要问题是某些核设施厂址确定论方法和概率论方法评价结果的显著差异。本文以我国的一些核电厂址为例,分析了确定论和概率论方法评价结果的控制性因素,分析结果表明,反应谱的周期较小时,主要受距厂址较近的发震构造(地震构造区)、潜在震源区控制;随着反应谱周期的增大,距厂址较远的区域性发震构造、高震级潜在震源区的影响逐步增大。通过分解变量MRs对地震动年平均超越概率(HT4)的相对贡献,给出了变量的边际分布和联合分布,说明了变量的分布特征,指出了评价结果差异的主要影响因素为单位面积上高震级档地震年平均发生率和衰减关系的截断水平。根据核设施结构基于性能抗震设计方法的应用要求,以地震引起堆融的年平均概率为目标,推导了反应谱调整系数公式,根据推导结果和中美两国厂址地震危险性曲线变化趋势的对比分析,建立了适用于我国的核设施结构抗震设计反应谱调整系数的近似公式。核电厂地震概率安全评价中的主要问题是概率地震危险性分析中的不确定性处理和表达。论文分析了地震动预测模型截断水平对概率地震危险性分析结果的影响,讨论了厂址地震危险性分析结果的分布形式;验证了随机振动理论方法的适用性,采用随机振动理论方法研究了土层地震反应分析中土层剖面模型参数的不确定性对评价结果的影响;介绍了美国中东部地区概率地震危险性分析认知不确定性处理采用的逻辑树方法,实现了逻辑树模型中多方案的权重确定方法,讨论了该方法的适用范围。关于认知不确定性处理,针对逻辑树模型在实际工程应用中存在的逻辑问题。基于稳定大陆地区最大震级和高震级档地震年平均发生率的研究进展,随机生成完整的地震目录,从中进行小样本抽样,分析了6值和高震级档地震年平均发生率的分布范围,研究了逻辑树模型中相互关联节点分支间的组合问题。根据稳定大陆地区最大震级先验分布的研究成果,利用破坏性地震目录计算似然函数,采用Bayesian方法,初步估计了对我国内陆核电厂址有重要影响的长江中游地震带最大震级的分布。关于抗震裕度评价中的抗震裕度地震确定问题,分析了我国核电厂址的地震危险性背景和不同堆型的抗震设计特点,以某核电厂址为例,采用多种方法确定了抗震裕度地震。根据分析计算结果,按照抗震裕度评价的目的、厂址地震危险性特征、堆型的抗震设计特点,给出了适用的方法和抗震裕度地震谱型。     

考虑俯冲带潜在震源区的地震危险性算法研究及在中国海域的应用

本文研究了俯冲带潜在震源区离散化方法及考虑俯冲带高震级地震震源破裂面和震源深度的场点地震动计算方法,推导了俯冲带潜在震源区地震危险性计算公式,并使用中国海域及邻区地震危险性模型进行地震危险性试算.结果表明,本文建立的考虑俯冲带潜在震源区的地震危险性算法能够实现场点地震危险性计算时对俯冲带高震级地震震源破裂面和震源深度的...     

地震统计区划分不确定性对场点地震危险性计算的影响

地震统计区是考虑时空不均匀性的概率地震危险性分析方法特有的概念,是确定地震活动性统计规律的基本统计单元.由于地震统计区在概念以及划分原则上存在较大的认识不确定性,因此,对场点地震危险性分析结果会产生不可忽视的影响.本研究的目的就是通过分析得到对这种影响的相对明晰的量化认识,以利于实际工作参考.     

概率地震危险性分析中参数不确定性研究

本文宗旨是探讨概率地震危险性分析方法中主要地震活动性参数的不确定性及其影响。为此 ,重点研究了地震统计区划分中的不确定性及其影响、地震统计区参数 b值的不确定性及其影响 ,以及空间分布函数对地震活动性参数导致的不确定性的影响。文中指出 ,地震统计区概念是考虑时空不均匀性的概率地震危险性分析方法中特有的概念 ,是对概率地震危险性分析方法在考虑地震活动空间分布不均匀性方面的发展。虽然它源于我国的地震带划分概念 ,但是 ,却明显区别于地震带。文中强调了地震带划分是地震孕育发生环境研究的重要基础 ,而地震统计区仅只服务…     

成都市地震危险性分析

本文以第三代地震区划图的编图思路为基础,采用考虑地震活动时空非均匀性的地震危险性分析方法进行成都市地震危险性评价。首先根据成都市及邻区的地震地质、地球物理和地震活动特征,确定不同震级上限Mu的潜在震源区;再估计各地震带的b值、地震年发生率及地震年均发生率分配函数;然后建立适合于成都市及邻区地震动(或烈度)衰减特征的等效圆、椭圆、长椭圆和断层破裂4种衰减模型。最后,采用考虑时空非均匀的地震危险性概率分析模型,评价了成都市不同超越概率的地震烈度。     

基于地震带细致划分为地震构造区的概率地震危险性分析

在我国当前地震安全性评价中,普遍使用考虑地震活动时空不均匀性的概率地震危险性分析方法(CP-SHA),它规定以地震带为统计区域计算地震活动性参数b值和v4值。正在编制的中国地震动区划图(五代图)提出了针对潜在震源区进行三级划分原则:划分地震带、地震带上划分地震构造区、地震构造区内再划分潜在震源区。本文提出以地震构造区为统计区域回归统计方法计算b值和v4值,然后进行概率危险性分析计算,这样得到的结果可能更为合理。     

珠江三角洲地震烈度概率危险性分析

根据我国东南沿海区域地质构造背景、地震活动的时空分布特征，对珠江三角洲地区的地震烈度水平进行概率危险性分析。基于区域内各统计单元及其潜在震源之间地震活动的时空非均匀性，本文给出的结果具有特定的统计意义。     

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.     

Uncertainty Analysis and Expert Judgment in Seismic Hazard Analysis

The large uncertainty associated with the prediction of future earthquakes is usually regarded as the main reason for increased hazard estimates which have resulted from some recent large scale probabilistic seismic hazard analysis studies (e.g. the PEGASOS study in Switzerland and the Yucca Mountain study in the USA). It is frequently overlooked that such increased hazard estimates are characteristic for a single specific method of probabilistic seismic hazard analysis (PSHA): the traditional (Cornell?CMcGuire) PSHA method which has found its highest level of sophistication in the SSHAC probability method. Based on a review of the SSHAC probability model and its application in the PEGASOS project, it is shown that the surprising results of recent PSHA studies can be explained to a large extent by the uncertainty model used in traditional PSHA, which deviates from the state of the art in mathematics and risk analysis. This uncertainty model, the Ang?CTang uncertainty model, mixes concepts of decision theory with probabilistic hazard assessment methods leading to an overestimation of uncertainty in comparison to empirical evidence. Although expert knowledge can be a valuable source of scientific information, its incorporation into the SSHAC probability method does not resolve the issue of inflating uncertainties in PSHA results. Other, more data driven, PSHA approaches in use in some European countries are less vulnerable to this effect. The most valuable alternative to traditional PSHA is the direct probabilistic scenario-based approach, which is closely linked with emerging neo-deterministic methods based on waveform modelling.     

Geodetic Strain Observations and Return Period of the Strongest Earthquakes of a Given Seismic Source Zone

We present the basis for a method for estimating the return period of large and medium earthquakes that is independent of current deterministic and probabilistic approaches. The two standard techniques of seismic hazard assessment??probabilistic seismic hazard assessment (PSHA) and deterministic seismic hazard assessment (DSHA)??suffer from limited knowledge of seismic prehistory. A further weakness of PSHA is its requirement of homogeneous seismic activity within a seismic zone. Moreover, PSHA and DSHA were developed for seismically active areas and, thus, cannot reliably be used in areas of medium and low activity. In this paper we propose the combined use of geodetic strain rate data and the seismic moment data set determined for past seismic events. This combination represents a new and independent approach to estimation of future seismic activity. Using a modified version of Kostrov??s (Phys Solid Earth 1:23?C40, 1974) equation and the catalogue of seismic moments, the minimum return period of the strongest earthquakes of a source area is estimated.     

Seismic Hazard Assessment: Issues and Alternatives

Seismic hazard and risk are two very important concepts in engineering design and other policy considerations. Although seismic hazard and risk have often been used interchangeably, they are fundamentally different. Furthermore, seismic risk is more important in engineering design and other policy considerations. Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space and to provide seismic hazard estimates for seismic risk assessment and other applications. Although seismic hazard assessment is more a scientific issue, it deserves special attention because of its significant implication to society. Two approaches, probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA), are commonly used for seismic hazard assessment. Although PSHA has been proclaimed as the best approach for seismic hazard assessment, it is scientifically flawed (i.e., the physics and mathematics that PSHA is based on are not valid). Use of PSHA could lead to either unsafe or overly conservative engineering design or public policy, each of which has dire consequences to society. On the other hand, DSHA is a viable approach for seismic hazard assessment even though it has been labeled as unreliable. The biggest drawback of DSHA is that the temporal characteristics (i.e., earthquake frequency of occurrence and the associated uncertainty) are often neglected. An alternative, seismic hazard analysis (SHA), utilizes earthquake science and statistics directly and provides a seismic hazard estimate that can be readily used for seismic risk assessment and other applications.     

Neo-Deterministic and Probabilistic Seismic Hazard Assessments: a Comparison over the Italian Territory

Estimates of seismic hazard obtained using the neo-deterministic approach (NDSHA) and the probabilistic approach (PSHA) are compared for the Italian territory. The NDSHA provides values larger than those given by the PSHA in areas where large earthquakes are observed and in areas identified as prone to large earthquakes, but lower values in low-seismicity areas. These differences suggest the adoption of the flexible, robust and physically sound NDSHA approach to overcome the proven shortcomings of PSHA, thus allowing for a reliable seismic hazard estimation, especially for those areas characterized by a prolonged quiescence, i.e. in tectonically active sites where events of only moderate size have occurred in historical times.     

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.     

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.     

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.      

On the declustering methods of seismic catalogue — an application over Indian subcontinent

Journal of Seismology - Seismic catalogue preparation is one of the important steps of probabilistic seismic hazard assessment (PSHA). Catalogue preparation includes homogenization and declustering...     

Application of a Monte‐Carlo simulation approach for the probabilistic assessment of seismic hazard for geographically distributed portfolio

The conventional integral approach is very well established in probabilistic seismic hazard assessment (PSHA). However, Monte‐Carlo (MC) simulations can become an efficient and flexible alternative against conventional PSHA when more complicated factors (e.g. spatial correlation of ground shaking) are involved. This study aims at showing the implementation of MC simulation techniques for computing the annual exceedance rates of dynamic ground‐motion intensity measures (GMIMs) (e.g. peak ground acceleration and spectral acceleration). We use multi‐scale random field technique to incorporate spatial correlation and near‐fault directivity while generating MC simulations to assess the probabilistic seismic hazard of dynamic GMIMs. Our approach is capable of producing conditional hazard curves as well. We show various examples to illustrate the potential use of the proposed procedures in the hazard and risk assessment of geographically distributed structural systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Updated seismic hazard assessment of Tunisia

Modern earthquake loss models make use of earthquake catalogs relevant to the seismic hazard assessment upon seismicity and seismotectonic analysis. The main objective of this paper is to investigate a recently compiled catalog (National Institute of Meteorology or INM catalog: 412-2011) and to generate seismic hazard maps through classical probabilistic seismic hazard assessment (PSHA) and smoothed-gridded seismicity models for Tunisia. It is now established with the local earthquake bulletin that the recent seismicity of Tunisia is sparse and moderate. Therefore, efforts must be undertaken to elaborate a robust hazard analysis for risk assessment and seismic design purposes. These recommendations follow the recently published reports by the World Bank that describe the seismic risk in Tunis City as being beyond a tolerable level with an MSK intensity level of VII. Some attempts were made during the past two decades to assess the seismic hazard for Tunisia and they have mostly failed to properly investigate the historical and instrumental seismicity catalog. This limitation also exists for the key aspect of epistemic and random uncertainties impact on the final seismic hazard assessment. This study also investigates new ground motion prediction equations suitable for use in Tunisia. The methodology applied herein uses, for the first time in PSHA of Tunisia, seismicity parameters integrated in logic tree framework to capture epistemic uncertainties through three different seismic source models. It also makes use of the recently released version of OpenQuake engine; an open-source tool for seismic hazard and risk assessment developed in the framework of the Global Earthquake Model.