基于地震危险性分析的场地地震动持时特性研究

通过地震危险性分析计算,认为场地震动力持时主要决定于近场地震影响,潜在震源区震级上限越大,场地地震动持时越大,潜在震源区其它地震活动性参数（年发生率、起算震级、ｂ值）减小或设防水准降低,场地地震动持时增加,且地震动持时增加幅度较小。     

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...     

青藏工程走廊地震危险性对比分析及区划

潜在震源区地震活动性参数、地震动衰减关系对地震危险性分析结果至关重要。以中国第五代地震动区划图潜在震源区划分方案为基础,采用2类震级分档分别建立自编及五代图潜在震源区空间分布函数,收集4组青藏高原及周缘地区地震动衰减关系,采用不同组合对青藏工程走廊沿线的81个场点进行概率地震危险性分析计算,得到50年超越概率10%(地震重现期475年)的各场点基岩地震动峰值加速度(PGA),并转换为一般场地(Ⅱ类)PGA,对计算结果进行对比分析,并与第五代地震动区划图归档上下限值进行比较。结果显示:采用我国西部地区地震动衰减关系计算得到的PGA最大,采用云南地区地震动衰减关系得到的PGA最小,采用川藏地区及青藏高原东北缘地震动衰减关系时居中;在同一地震动衰减关系下,采用自编空间分布函数计算得到的PGA普遍略大于采用第五代图空间分布函数时;在震级上限为8.5的潜在震源区及附近地区,潜在震源区空间分布函数震级分档对计算结果有显著影响。综合分析表明,采用自编Ⅱ型震级分档空间分布函数方案与川藏地区地震动衰减关系组合方案的计算结果最为理想。最后,采用该组合方案对青藏工程走廊50年超越概率10%的基岩场地PGA及一般场地PGA进行了区划。     

唐山区域概率地震危险性研究

依据历史地震重演和构造类比原则对唐山地区进行潜在震源区划分,共确定出5个对研究区影响较大的潜在震源区。在确定地震活动性参数和地震动衰减关系后,将研究区网格化成60个均匀的独立场地单元,计算每个场地单元未来可能遭受相应超越概率的地震动峰值加速度;通过插值分析,将研究区原有地震区划中的基岩峰值加速度等值线间隔由0.05 g进一步细化为0.01 g;得到研究区50年超越概率为10%的基岩水平地震动峰值加速度分布图,表明唐山8.0级潜在震源区对研究区未来影响最大。     

山东某场地概率地震危险性分析

利用概率地震危险性分析(CPSHA)方法,对山东某场地进行地震危险性分析,通过对该场地划分潜在震源区,确定地震活动性参数及地震动衰减关系,计算分析地震危险性概率,基本确定对该场地地震动峰值加速度起主要贡献的几个潜在震源区及贡献值,并确定该场地50年超越概率10%的水平向基岩地震动加速度峰值。结果发现,CPSHA方法以具体的构造尺度和更加细致的构造标志来划分潜在震源区,使潜在震源区规模缩减,从而更能反映地震活动在空间分布上的不均匀性。     

地震危险性分析中潜在震源区范围与震级上限的不确定性分析

目前进行的地震危险性分析计算中, 潜在震源区范围和震级上限的确定过程中存在很大的不确定性。 采用二级划分和三级划分潜在震源区的方法, 对潜在震源区范围不确定性进行了研究; 用震级上限的单边正态分布模型代替固定的震级上限模型, 分析了这种改进对地震危险性分析结果的影响及其工程意义。 结果表明, 用三级划分潜源的方法代替二级划分潜在震源方法可降低局部地区的地震危险性, 对于在潜在震源区附近选址和降低工程成本有重要意义。 震级上限的改进, 使得地震危险性降低, 这对百年使用年限的工程更具有实用性。     

地震危险性分析中几个重要环节的关联性

为进一步揭示地震统计区划分、潜在震源区划分和地震活动性参数确定三者的关联性,在100deg;E～120deg;E和29deg;N～42deg;N范围内,寻找出21个位于不同位置、具有一定代表性的场点,研究在非均匀分布与均匀分布两种模型下,地震统计区活动性参数的不确定性对这些场点危险性估计的影响. 综合本次与以往的研究结果表明,不同的地震统计区划分方案会改变一个统计区所包含的地震资料,加上地震统计时段选取的不确定性,会导致统计区地震活动性参数估计的不确定性. 这种不确定性变化越大,均匀分布模型对场点危险性估计所产生的不确定影响也越大,也即地震统计区划分环节起主要作用. 在一个地震统计区内,划分潜在震源区和空间分布函数的不等权分配,提高了有可能发生大地震地方及其附近地区地震动参数的估计值. 在这些地方,潜在震源区划分不确定性的影响是很明显的,尤其对场点地震动参数（如烈度）绝对值的影响更为显著,也即潜在震源区划分环节起主要作用. 一般来说,潜在震源区划分环节的影响仅对最高和次高震级上限潜在震源区内的场点及最高震级上限潜在震源区附近的场点起主要作用,而对那些处于低震级上限潜在震源中的场点,则还是地震统计区划分不确定性的影响大于潜在震源区划分不确定性的影响.       

基于数学建模的潜在地震破裂面源检测方法研究

大多数地震破裂面源检测方法都是通过简化地震震源,将地震震源表示成线源或者点源,无法有效描述地震带地震破裂面源产状和大小,不适用地震震级较大的情况下地震危险性检测。因此提出基于数学建模的潜在地震破裂面源检测方法,在地震震级较大时仍能检测出地震危险性概率。选取适宜的地震基岩水平峰值加速度衰减关系,分析地震震级、破裂长度、破裂宽度相互关系,确定地震引起的潜在地震破裂面源大小,计算给定地震动小于在场点处产生地震动的概率,将该概率同地震动加速度衰减关系结合,得到地震动年超越概率,分析地震危险性。经过实验检测发现,所提方法检测出的年超越概率与峰值加速度、最大震级有关,该概率能精准表示地震带地震破裂面源产状和大小,说明该方法检测地震危险性是合理的。     

乌鲁木齐及周边地区潜在震源区的确定

根据"乌鲁木齐市活断层探测与地震危险性评价"项目的成果,确定了乌鲁木齐及周边地区的发震构造模型。在此基础上,结合地震活动特征,根据地震重复及构造类比原则对乌鲁木齐市周围的潜在震源区进行了重新划分。由此,采用地震危险性概率分析方法计算乌鲁木齐市及周围县市的基岩峰值加速度,并进行地震动峰值加速度复核。由复核结果可以看出,此潜在震源区划分方案对乌鲁木齐市的影响不大,但对阜康市的影响较大,使该市地震动峰值加速度由原来的0.15g变化为0.20g。     

巴基斯坦沿海地区地震危险性分析

通过确定性和概率性方法，对发展迅速的巴基斯坦沿海地区进行了地震危险性评估．根据该地区的地震构造和地质条件，确定了5个地震区域的11个断层作为该地区的潜在震源，计算了每个潜在震源的最大可能震级．根据与之相关震源的最大可信震级，计算了7个沿海城市的峰值加速度（PGA）．瓜达尔（Gwadar）和奥尔马腊（Ormara）的峰值加速度分别为0.21和0.25 g，处于地震危险性水平较高的地区；杜尔伯德（Turbat）和卡拉奇（Karachi）位于地震危险性水平较低的地区，峰值加速度小于0.1 g．同时，分别绘制了50年和100年超越概率为10％的PGA区划图，区划图的分区间隔为0.05 g．      

Regional and local seismic hazard assessment

Recent earthquakes such as the M_JMA 7.2 Hyogo-ken Nambu earthquake and the M 7.4 Kocaeli earthquake demonstrate once again the need to include detailed soil investigation into hazard evaluation, that is the need of microzonation. Seismic hazard assessment evaluated at a regional scale generally does not consider soil effects but only in a limited way using an attenuation law that can be ‘soft soil’ or ‘rock’. However, the relevant role of seismic hazard in the assessment of seismic coefficients for the definition of the actions in seismic codes must be properly considered. That is to say, the level of protection of buildings is proportional to a definite level of hazard (generally considered to be the ground motion with 10% probability of exceedence in 50 years). When a microzonation is performed, this criterion cannot be ignored, therefore, a clear linkage must be established between hazard (regional scale) and microzonation. The crucial point is represented by the reference motion (or input motion) to be used for site effects analysis, that must be compatible with the regional seismic hazard. In this paper, three different approaches for reference motion evaluation are analysed: probabilistic; stochastic; and deterministic. Through the case history of Fabriano microzonation the three approaches are compared. It is shown that each approach presents advantages and disadvantages with respect to the others. For example, the probabilistic approach (the reference motion is directly derived from the expected response spectra for a given return period) is linked with hazard, but produces an overestimation in short periods range, while the deterministic approach correctly simulates the wave propagation, but it ends with a kind of conditional probability. Until now, clear criteria to choose the right approach do not appear to exist and the expert experience is of fundamental importance.     

Probabilistic seismic hazard assessment of the Pyrenean region

A unified probabilistic seismic hazard assessment (PSHA) for the Pyrenean region has been performed by an international team composed of experts from Spain and France during the Interreg IIIA ISARD project. It is motivated by incoherencies between the seismic hazard zonations of the design codes of France and Spain and by the need for input data to be used to define earthquake scenarios. A great effort was invested in the homogenisation of the input data. All existing seismic data are collected in a database and lead to a unified catalogue using a local magnitude scale. PSHA has been performed using logic trees combined with Monte Carlo simulations to account for both epistemic and aleatory uncertainties. As an alternative to hazard calculation based on seismic sources zone models, a zoneless method is also used to produce a hazard map less dependant on zone boundaries. Two seismogenic source models were defined to take into account the different interpretations existing among specialists. A new regional ground-motion prediction equation based on regional data has been proposed. It was used in combination with published ground-motion prediction equations derived using European and Mediterranean data. The application of this methodology leads to the definition of seismic hazard maps for 475- and 1,975-year return periods for spectral accelerations at periods of 0 (corresponding to peak ground acceleration), 0.1, 0.3, 0.6, 1 and 2 s. Median and percentiles 15% and 85% acceleration contour lines are represented. Finally, the seismic catalogue is used to produce a map of the maximum acceleration expected for comparison with the probabilistic hazard maps. The hazard maps are produced using a grid of 0.1°. The results obtained may be useful for civil protection and risk prevention purposes in France, Spain and Andorra.     

Earthquake magnitude or seismic moment in seismic hazard evaluation?

Seismic hazard analysis requires the estimation of the probabilities that earthquakes will take place within a region of interest, and the expected level of ground motion which will be received at a site during the nextt years. The earthquake magnitude has been used as a basic parameter, because it is available, under the assumption that the earthquake occurrence is a compound Poisson process with exponential or multinomial distribution of magnitude.For improving the hazard prediction, we used the seismic moment as a basic parameter to estimate the mean rate, , of occurrence of earthquakes in a function of seismic moment rate and slip rate released in a seismogenic region.As an illustration of the model, the seismic hazard analysis at different sites in and around the Gulf of Corinth, central Greece, is presented on the basis of the earthquake magnitude and the seismic moment. Comparison of the results shows that determination of the mean rate of earthquake occurrence, using the conventional Gutenberg-Richter recurrence model, underestimates the seismic hazard at a site.     

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.     

A new seismic hazard analysis using FOSM algorithms

From recent lessons, it is evident that earthquake prediction is immature and impractical as of now. Under the circumstances, seismic hazard analysis is considered a more practical approach for earthquake hazard mitigation, by estimating the annual rate of earthquake ground motions (or seismic hazard) based on seismicity and other geological evidences. Like other earthquake studies for the high-seismicity region around Taiwan, this study aims to conduct a new seismic hazard assessment for the region using the well-established FOSM (first-order second-moment) algorithm, on the record of 55,000 earthquakes observed in the past 110 years. The new seismic hazard analysis from a different perspective shows that the annual rate for earthquake-induced PGA to exceed the current design value (i.e., 0.23g) in two major cities in Taiwan should be relatively low, with it no greater than 0.0006 per year. Besides, the FOSM estimates were found very close to those with Monte Carlo Simulation (MCS), mainly because the skewness of the three random variables (i.e., earthquake magnitude, location, and model error) considered in the probabilistic analysis is not very large.     

Characterization of seismic hazard and structural response by energy flux

Seismic safety of structures depends on the structure's ability to absorb the seismic energy that is transmitted from ground to structure. One parameter that can be used to characterize seismic energy is the energy flux. Energy flux is defined as the amount of energy transmitted per unit time through a cross-section of a medium, and is equal to kinetic energy multiplied by the propagation velocity of seismic waves. The peak or the integral of energy flux can be used to characterize ground motions. By definition, energy flux automatically accounts for site amplification. Energy flux in a structure can be studied by formulating the problem as a wave propagation problem. For buildings founded on layered soil media and subjected to vertically incident plane shear waves, energy flux equations are derived by modeling the building as an extension of the layered soil medium, and considering each story as another layer. The propagation of energy flux in the layers is described in terms of the upgoing and downgoing energy flux in each layer, and the energy reflection and transmission coefficients at each interface. The formulation results in a pair of simple finite-difference equations for each layer, which can be solved recursively starting from the bedrock. The upgoing and downgoing energy flux in the layers allows calculation of the energy demand and energy dissipation in each layer. The methodology is applicable to linear, as well as nonlinear structures.     

Probabilistic seismic hazard assessment of Switzerland: best estimates and uncertainties

We present the results of a new genera tion of probabilistic seismic hazard assessment for Switzerland. This study replaces the previous intensity-based generation of national hazard maps of 1978. Based on a revised moment-magnitude earthquake catalog for Switzerland and the surrounding regions, covering the period 1300–2003, sets of recurrence parameters (a and b values, M _max ) are estimated. Information on active faulting in Switzerland is too sparse to be used as source model. We develop instead two models of areal sources. The first oriented towards capturing historical and instrumental seismicity, the second guided largely by tectonic principles and express ing the alterative view that seismicity is less stationary and thus future activity may occur in previously quiet regions. To estimate three alterna tive a and b value sets and their relative weighting, we introduce a novel approach based on the modified Akaike information criterion, which allows us to decide when the data in a zone deserves to be fitted with a zone-specific b value. From these input parameters, we simulate synthetic earthquake catalogs of one-million-year duration down to magnitude 4.0, which also reflect the difference in depth distribution between the Alpine Foreland and the Alps. Using a specific predictive spectral ground motion model for Switzerland, we estimate expected ground motions in units of the 5% damped acceleration response spectrum at frequencies of 0.5–10 Hz for all of Switzerland, referenced to rock sites with an estimated shear wave velocity of 1,500 m/s² in the upper 30 m. The highest hazard is found in the Wallis, in the Basel region, in Graubünden and along the Alpine front, with maximum spectral accelerations at 5 Hz frequency reaching 150 cm/s² for a return period of 475 years and 720 cm/s² for 10,000 years. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Simplified method for generating slope seismic deformation hazard curve

A simplified method for generating slope deformation hazard curve that takes into account the variations of input parameters is presented in this paper. The main assumption in the new approach is that the occurrence of peak slope deformation is Poisson׳s process. The procedure is based on logic tree analysis, commercial software and routines programmed by the authors for generating sets of input files, and forming slope performance curve. The methodology was applied to a real landslide in order to demonstrate the advantages and limitations of the proposed approach. The results of the analysis showed the influence of the certain input factors on sliding displacement as well as the advantages of employing continuum mechanics approach.     

Strong ground acceleration seismic hazard in Greece and neighboring regions

In an early paper [Tectonophysics 117 (1985) 259] seismic hazard in Greece was analyzed using a relatively homogeneous earthquake catalogue spanning 1900–1978 and a strong motion attenuation relationship adapted to use in Greece. Improved seismic hazard analyses are obtained here using Gumbel's asymptotic extreme value distribution applied to peak horizontal ground acceleration occurrence, but now taking into account the increased length and quality of earthquake catalogue data spanning 1900–1999 and the burgeoning information on earthquake strong motion data and attenuation relationships appropriate for Europe and, explicitly, Greece. Seismic acceleration hazard results tabulated for six cities reveal (e.g. using arbitrarily the 50-year p.g.a. with 90% probability of not being exceeded) changes of about 10% in the new calculated values: two cities show an increase and four a decrease. These are relatively small and reassuring adjustments.Inspection of the available attenuation relationships leads to a preference for the models of Theodulidis and Papazachos, particularly with the model modification to produce a ‘stiff soil’ site relationship, as these relationships explicitly exploit the Greek strong motion database. Isoacceleration maps are produced for Greece as a whole from each attenuation relationship inspected. The final set of maps based on the Theodulidis and Papazachos models provide a foundation for comparison with the Seismic Hazard Zones adopted in the New Greek Seismic Code where scope can be found to modify zone shape and the level at which p.g.a.s are set. It should be noted that the generation of the present isoacceleration maps is based on a seismogenic zone-free methodology, independent of any Euclidean zoning assumptions.