Research on the principle and methodology of seismic zonation

Based on the cognizance of the temporal-spatial inhomogeneity of seismicity in North China, adopting the results of earthquake prediction in the past two decades and the currently used methods of seismic hazard analysis, and after some zonation trials in North China, some improvements on the zonation principle and methodology were made:

1. Seismic zones were taken as statistic units where seismicity parameters were obtained. Tendency analysis was introduced. Earthquake annual average occurrence rates were estimated corresponding to the seismicity level in the future period;
2. Average annual earthquake occurrence rates for a given magnitude interval of a specific seismic zone were assigned to potential sources considering the relative risk level among these sources. Thus, the risk of great earthquakes can be estimated.
3. The probabilistic spatial distribution function under the condition of magnitude interval was suggested to reflect the temporal and spatial inhomogeneity of seismicity.
4. An orientation function in the seismic hazard analysis model was adopted, which reflects the real condition of earthquake foci in China.

     

地震区划原则和方法的研究——以华北地区为例.

本文基于对我国华北地区地震活动在时间和空间不均匀分布的认识,吸收了近20年来地震预测方面的科研成果,采用目前国际通用的地震危险性概率分析方法,通过对华北区划的试验,对地震区划的原则和方法提出了如下改进: 1.以地震带作为地震活动性参数的统计单元.引入地震活动趋势估计因素,评定表征地震活动水平的年平均发生率,以使区划结果同预测未来时间段地震活动水平相适应; 2.采用按震级挡次分配各潜在震源区的年平均发生率,可以合理地评估高震级地震的危险程度; 3.采用以震级挡次为条件概率的空间分布函数,刻画地震带内各潜在震源区之间发生相应震级挡次地震的相对危险程度,使区划结果更好地反映地震活动在时间和空间上不均匀性分布的特点; 4.在地震危险性分析计算中,引入了方向性函数项,使得分析模型更接近我国地震震源的实际情况.      

基于凸集模型的界限pushover分析

结构的抗震性能评估中包含许多不确定性因素。当掌握的不确定性信息较少时,概率模型结果是值得怀疑的。本文首先采用双界限凸集模型考虑地面运动加速度峰值和反应谱特征周期的不确定性,并结合我国现行抗震设计规范中的反应谱,求得结构层间剪力的变异区间,在此基础上给出了一种新的界限侧向加载方式;并进一步将凸集理论融于pushover分析过程中,分析了由pushover得到的结构能力的界限变化区间。结果表明本文給出的界限pushover方法能给出性态指标的变化区间,是一种更客观可靠的抗震性能评估方法。     

十年尺度地震危险性概率预测方法的初步研究

在十年尺度（５—１０年）地震危险性预测中，需要处理众多的不确定因素。受这些不确定因素的约束，地震预测的结果必然带有相当的不确定性，因此应该用概率分析的方法进行预测。考虑地震发生的时间、空间和强度的非均匀性及相关特征和地震危险性长期背景（地质、地球物理场等因素）与地震发生前兆的概率结合，提出了十年尺度地震危险性预测的概率模型。考虑资料的不均匀性和适宜不同地区的地震前兆方法的差异，本文还提出了概率预测模型简化形式，以满足全国不同地区的需要。本文以华北北部地区为例讨论了该模型的实际应用。文中提出的方法可以用于全国十年尺度地震危险性的概率预测。根据本项研究提供的结果和计算程序，可以满足地震对策和地震损失估计对地震中长期概率预测的需要。     

Research on determining the annual earthquake occurrence rates of potential seismic source areas

To actually reflect the seismic temporal-spatial inhomogeneity of intra continental strong earthquakes of North China in seismic hazard analysis, several seismological and geological characteristics have been selected and quantized to describe the seismicity features in time and space of every magnitude interval with the thought of dividing the interesting magnitude range into several intervals and using of spatial probability distribution function. A component analysis method with orthogonal transformation is introduced to avoid the repeated use of the same element and the subjective effects in determining the annual earthquake occurrence rates of earthquake. By passing synthetic fuzzy judgement on the nonintercorrelated new characteristics, the annual occurrence rates of every magnitude interval of each potential source area are obtained associated with the adjustments of earthquake reducing process after the occurrence ofM>7 quake. An intensity map of the Beijing-Tianjin-Zhangjiakou area is calculated as an example which shows a close coincidence with the seismic temporal-spatial inhomogeneity of North China. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 496–504, 1991.     

Earthquake hazard and risk assessment based on Unified Scaling Law for Earthquakes: Greater Caucasus and Crimea

We continue applying the general concept of seismic risk analysis in a number of seismic regions worldwide by constructing regional seismic hazard maps based on morphostructural analysis, pattern recognition, and the Unified Scaling Law for Earthquakes (USLE), which generalizes the Gutenberg-Richter relationship making use of naturally fractal distribution of earthquake sources of different size in a seismic region. The USLE stands for an empirical relationship log₁₀N(M, L)?=?A?+?B·(5 – M)?+?C·log₁₀L, where N(M, L) is the expected annual number of earthquakes of a certain magnitude M within a seismically prone area of linear dimension L. We use parameters A, B, and C of USLE to estimate, first, the expected maximum magnitude in a time interval at seismically prone nodes of the morphostructural scheme of the region under study, then map the corresponding expected ground shaking parameters (e.g., peak ground acceleration, PGA, or macro-seismic intensity). After a rigorous verification against the available seismic evidences in the past (usually, the observed instrumental PGA or the historically reported macro-seismic intensity), such a seismic hazard map is used to generate maps of specific earthquake risks for population, cities, and infrastructures (e.g., those based on census of population, buildings inventory). The methodology of seismic hazard and risk assessment is illustrated by application to the territory of Greater Caucasus and Crimea.     

确定潜在震源区地震年平均发生率的方法研究

为了在地震危险性分析方法中,较好地反映大陆内部地震活动的时空不均匀性,按照震级分档和空间概率分布函数的思路,本文选取并量化了多个地震、地质特征,以描述各震级档地震活动在时间上和空间上的性质.为避免同一因素的重复使用和主观作用的介入,文中引入了分量分析方法对特征进行正交变换.对变换得到的互不相关的新特征进行模糊综合评判,再结合七级以上强震发生后的减震作用,确定了各潜在震源区各震级档的地震年平均发生率作为例子,试算了京-津-唐-张地区的地震烈度区划图.该例子说明,本文的分析方法,不仅能反映华北地区地震活动的时空不均匀性,还避免了特征量的重复使用和专家判断的影响      

Parametric-historic Procedure for Probabilistic Seismic Hazard Analysis Part I: Estimation of Maximum Regional Magnitude mmax

—A new methodology for probabilistic seismic hazard analysis (PSHA) is described. The approach combines the best features of the "deductive" (Cornell, 1968) and "historical" (Veneziano et al., 1984) procedures. It can be called a "parametric-historic" procedure.¶The maximum regional magnitude m _max is of paramount importance in this approach and Part I of our work presents some of the statistical techniques which can be used for its evaluation. The work is an analysis of parametric procedures for the evaluation of m _max, when the form of the magnitude distribution is specified. For each of the formulae given there are notes on its origin, assumptions made of its derivation, and some comparisons. The statistical concepts of bias and variance are considered for each formula, and appropriate expressions for these are also given. Also, following Knopoff and Kagan (1977), we shall demonstrate why there must be a finite upper bound to the largest seismic event if the Gutenberg-Richter frequency-magnitude relation is accepted.     

Predicted ground motion after the L��Aquila 2009 earthquake (Italy, M w 6.3): input spectra for seismic microzoning

After the April 6th 2009 L’Aquila earthquake (M _w 6.3), where 306 people died and a further 60,000 were displaced, seismic microzoning investigations have been carried out for towns affected by a macroseismic intensity equal to or greater than 7 MCS. Based upon seismotectonic data, historical seismicity and strong motion records, we defined input spectra to be used in the numerical simulations of seismic microzoning in four key municipalities, including the town of L’Aquila. We adopted two main approaches: uniform hazard response spectra are obtained by a probabilistic seismic hazard assessment introducing some time-dependency for individual faults on the study area; a deterministic design spectrum is computed from magnitude/distance pairs extracted by a stationary probabilistic analysis of historical intensities. The uniform hazard spectrum of the present Italian building code represents the third, less restrictive, response spectrum to be used for the numerical simulations in seismic microzoning. Strong motions recordings of the main shock of the L’Aquila sequence enlighten the critical role played by both the local response and distances metric for sites located above a seismogenic fault; however, these time-histories are compatible with the uncertainties of a deterministic utilization of ground motion predictive equations. As recordings at very near field are rare, they cannot be neglected while defining the seismic input. Disaggregation on the non-Possonian seismotectonic analysis and on the stationary site-intensity estimates reach very similar results in magnitude-distance pairs identification; we interpret this convergence as a validation of the geology-based model by historical observations.     

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.     

Comparison of Bayesian estimates of peak ground acceleration (<Emphasis Type="Italic">A</Emphasis>max) with PSHA in Iran

Bayesian probability theory is an appropriate and useful method for estimating parameters in seismic hazard analysis. The analysis in Bayesian approaches is based on a posterior belief, also their special ability is to take into account the uncertainty of parameters in probabilistic relations and a priori knowledge. In this study, we benefited the Bayesian approach in order to estimate maximum values of peak ground acceleration (A_max) also quantiles of the relevant probabilistic distributions are figured out in a desired future interval time in Iran. The main assumptions are Poissonian character of the seismic events flow and properties of the Gutenberg-Richter distribution law. The map of maximum possible values of A_max and also map of 90% quantile of distribution of maximum values of A_max on a future interval time 100 years is presented. According to the results, the maximum value of the A_max is estimated for Bandar Abbas as 0.3g and the minimum one is attributed to Esfahan as 0.03g. Finally, the estimated values in Bayesian approach are compared with what was presented applying probabilistic seismic hazard (PSH) methods based on the conventional Cornel (1968) method. The distribution function of A_max for future time intervals of 100 and 475 years are calculated for confidence limit of probability level of 90%.     

Preliminary Study on Probabilistic Prediction of Seismic Hazard in a Period of 10 Years

Many uncertainty factors need be dealt with in the prediction of seismic hazard for a 10-year period.Restricted by these uncertainties,the result of prediction is also uncertain to a certain extent,so the probabilistic analysis method of seismic hazard should be adopted.In consideration of the inhomogeneity of the time,location,and magnitude of future earthquakes and the probabilistic combination of the background of long-term seismic hazard(geology,geophysical field,etc.)and the precursors of earthquake occurrence,a model of probabilistic prediction of seismic hazard in a period of 10 years s proposed.Considering the inhomogeneity of data and earthquake precursors for different regions in China,a simplified model is also proposed in order to satisfy the needs of different regions around the country.A trial in North China is used to discuss the application of the model.The method proposed in this paper can be used in the probabilistic prediction of seismic hazard in a period of 10 years.According to the     

Seismic Hazard and Risk Assessments for Beijing�CTianjin�CTangshan, China, Area

Seismic hazard and risk in the Beijing?CTianjin?CTangshan, China, area were estimated from 500-year intensity observations. First, we digitized the intensity observations (maps) using ArcGIS with a cell size of 0.1?×?0.1°. Second, we performed a statistical analysis on the digitized intensity data, determined an average b value (0.39), and derived the intensity?Cfrequency relationship (hazard curve) for each cell. Finally, based on a Poisson model for earthquake occurrence, we calculated seismic risk in terms of a probability of I????7, 8, or 9 in 50?years. We also calculated the corresponding 10 percent probability of exceedance of these intensities in 50?years. The advantages of assessing seismic hazard and risk from intensity records are that (1) fewer assumptions (i.e., earthquake source and ground motion attenuation) are made, and (2) site-effect is included. Our study shows that the area has high seismic hazard and risk. Our study also suggests that current design peak ground acceleration or intensity for the area may not be adequate.     

核设施地震危险性估计中的几个问题

总结了地震安全性估计方法的现状与发展趋势,指出我国在用确定性方法确定设计地震动时,有些不确定性并未考虑,不少主观决定并非总是足够安全的。文中推荐了概率方法。场地影响分析中,特别是座落于软基上的核设施,需要对输入面的选择及土层反应分析中的多种不确定因素进行考虑。最后指出场地地震相关反应谱对座落于软基上的核设施的重要意义,以及大远震与小近震对反应谱的不同影响     

Forward induced seismic hazard assessment: application to a synthetic seismicity catalogue from hydraulic stimulation modelling

The M _w 3.2-induced seismic event in 2006 due to fluid injection at the Basel geothermal site in Switzerland was the starting point for an ongoing discussion in Europe on the potential risk of hydraulic stimulation in general. In particular, further development of mitigation strategies of induced seismic events of economic concern became a hot topic in geosciences and geoengineering. Here, we present a workflow to assess the hazard of induced seismicity in terms of occurrence rate of induced seismic events. The workflow is called Forward Induced Seismic Hazard Assessment (FISHA) as it combines the results of forward hydromechanical-numerical models with methods of time-dependent probabilistic seismic hazard assessment. To exemplify FISHA, we use simulations of four different fluid injection types with various injection parameters, i.e. injection rate, duration and style of injection. The hydromechanical-numerical model applied in this study represents a geothermal reservoir with preexisting fractures where a routine of viscous fluid flow in porous media is implemented from which flow and pressure driven failures of rock matrix and preexisting fractures are simulated, and corresponding seismic moment magnitudes are computed. The resulting synthetic catalogues of induced seismicity, including event location, occurrence time and magnitude, are used to calibrate the magnitude completeness M _c and the parameters a and b of the frequency-magnitude relation. These are used to estimate the time-dependent occurrence rate of induced seismic events for each fluid injection scenario. In contrast to other mitigation strategies that rely on real-time data or already obtained catalogues, we can perform various synthetic experiments with the same initial conditions. Thus, the advantage of FISHA is that it can quantify hazard from numerical experiments and recommend a priori a stimulation type that lowers the occurrence rate of induced seismic events. The FISHA workflow is rather general and not limited to the hydromechanical-numerical model used in this study and can therefore be applied to other fluid injection models.     

An exploration of incorporating site response into PSHA—Part I: Issues related to site response analysis methods

This paper presents a series of analyses for the evaluation of the ground response of two NEHRP class D sites, subjected to shaking by a large number of strong ground-motion records. The two investigated sites have very distinct profiles, but they are characterised by almost identical V_s30 values. The site response analyses are performed using various methods of analysis and input parameters in order to explore the sensitivity of the ground response estimates and to identify the dominating parameters. Equivalent linear analysis is performed using different sets of dynamic soil properties curves, while nonlinear analysis is performed using different target dynamic soil curves, viscous damping formulations and fitting procedures for the constitutive model parameters. Particular focus is given to the sensitivity of the response when soil sites are subjected to high-intensity shaking, a subject of particular interest when the prediction of surface ground motions with low annual probabilities of exceedance is the target of probabilistic seismic hazard analyses (PSHA). The site response analysis results of this paper are incorporated into the probabilistic framework of Bazzurro and Cornell [1] in our companion paper in order to assess their impact on the final soil surface hazard calculation.     

Seismic reliability of V‐braced frames: Influence of design methodologies

According to the most modern trend, performance‐based seismic design is aimed at the evaluation of the seismic structural reliability defined as the mean annual frequency (MAF) of exceeding a threshold level of damage, i.e. a limit state. The methodology for the evaluation of the MAF of exceeding a limit state is herein applied with reference to concentrically ‘V’‐braced steel frames designed according to different criteria. In particular, two design approaches are examined. The first approach corresponds to the provisions suggested by Eurocode 8 (prEN 1998—Eurocode 8: design of structures for earthquake resistance. Part 1: general rules, seismic actions and rules for buildings), while the second approach is based on a rigorous application of capacity design criteria aiming at the control of the failure mode (J. Earthquake Eng. 2008; 12 :1246–1266; J. Earthquake Eng. 2008; 12 :728–759). The aim of the presented work is to focus on the seismic reliability obtained through these design methodologies. The probabilistic performance evaluation is based on an appropriate combination of probabilistic seismic hazard analysis, probabilistic seismic demand analysis (PSDA) and probabilistic seismic capacity analysis. Regarding PSDA, nonlinear dynamic analyses have been carried out in order to obtain the parameters describing the probability distribution laws of demand, conditioned to given values of the earthquake intensity measure. Copyright © 2009 John Wiley & Sons, Ltd.     

Updating the Probabilistic Seismic Hazard Values of Northern Algeria with the 21 May 2003 <Emphasis Type="Italic">M</Emphasis> 6.8 Algiers Earthquake Included

The occurrence of the Algiers earthquake (M 6.8) of May 21, 2003, has motivated the necessity to reassess the probabilistic seismic hazard of northern Algeria. The fact that this destructive earthquake took place in an area where there was no evidence of previous significant earthquakes, neither instrumental nor historical, strongly encourages us to review the seismic hazard map of this region. Recently, the probabilistic seismic hazard of northern Algeria was computed using the spatially smoothed seismicity methodology. The catalog used in the previous computation was updated for this review, and not only includes information until June 2003, but also considers a recent re-evaluation of several historical earthquakes. In this paper, the same methodology and seismicity models are utilized in an effort to compare this methodology against an improved and updated seismic catalog. The largest mean peak ground acceleration (PGA) values are obtained in northernmost Algeria, specifically in the central area of the Tell Atlas. These values are of the order of 0.48 g for a return period of 475 years. In the City of Algiers, the capital of Algeria, and approximately 50 km from the reported epicenter of this latest destructive earthquake, a new mean PGA value of 0.23 g is obtained for the same return period. This value is 0.07 g greater than that obtained in the previous computation. In general, we receive greater seismic hazard results in the surrounding area of Algiers, especially to the southwest. The main reason is not this recent earthquake by itself, but the significant increase in the m_max magnitude in the seismic source where the city and the epicenter are included.     

Seismic Intensity Zoning Map of China (1990) and Its Explanation

The Seismic Intensity Zoning Map of China(1990)was based on the probabilistic method of seismic hazard analysis.In compiling the map,the characteristics of inhomogeneity of earthquake distribution both in space and time in China are considered sufficiently,and some necessary modifications in the model of seismic hazard analysis are carried out.Based on the analysis of the seismic activity and seismotectonic environment,26 seismic provinces are divided first as the statistical elements of the seismicity analysis; the seismic potential source areas are then divided in the seismic provinces.The 733 potential source areas with various upper limit magnitudes have been divided in the country.According to the reliable time domain of earthquake data with various magnitude intervals,the b values in magnitude-frequency relationship are calculated in the seismic provinces.According to the analysis of the inhomogeneity of seismicity distribution both in space and time,the annual average occurrence rates of the eart     

Using experimental data to reduce the single-building sigma of fragility curves: case study of the BRD tower in Bucharest, Romania

The lack of knowledge concerning modelling existing buildings leads to significant variability in fragility curves for single or grouped existing buildings. This study aims to investigate the uncertainties of fragility curves, with special consideration of the single-building sigma. Experimental data and simplified models are applied to the BRD tower in Bucharest, Romania, a RC building with permanent instrumentation. A three-step methodology is applied： （1） adjustment of a linear MDOF model for experimental modal analysis using a Timoshenko beam model and based on Anderson＇s criteria, （2） computation of the structure＇s response to a large set of accelerograms simulated by SIMQKE software, considering twelve ground motion parameters as intensity measurements （IM）, and （3） construction of the fragility curves by comparing numerical interstory drift with the threshold criteria provided by the Hazus methodology for the slight damage state. By introducing experimental data into the model, uncertainty is reduced to 0.02 considering Sd ） as seismic intensity IM and uncertainty related to the model is assessed at 0.03. These values must be compared with the total uncertainty value of around 0.7 provided by the Hazus methodology.