An evaluation of seismic hazard parameters in southern Turkey

To investigate the characteristics of earthquake hazard parameters as a means of identifying different zones of seismicity, we have compiled a catalogue of about 1850 moderate to large-sized earthquakes with magnitudes m4.0 or greater in southern Turkey for the time period from 1900 to 1990. Several methods have been applied to the earthquake catalogue to assess seismic hazard. The study area is divided into 77 overlapping cells of 2° size. Theoretical calculations were made for the prediction of maximum magnitude, intensity, b-values, strain energy release and corresponding m3 and peak ground acceleration levels for a given period of time. The resultant seismic hazard for each parameter is depicted as a contour map to indicate lateral variations in areas of seismic source. A combination and evaluation of various hazard parameters resulted in more reasonable estimates of hazard. It is found that the most hazardous seismic zones are the Rhodes and Burdur zones where the level of peak ground acceleration reaches up to 280 cm s-2 for an average return period of 100 years.     

中国海域地震区划及关键问题研究

国家重点研发计划项目《海域地震区划关键技术研究》已实施3年，进入项目结题阶段，已形成海域地震区划方法与技术体系，研究成果为即将开展的中国海域地震区划图编制工作提供技术支撑。项目组分析和探讨了海域地震区划研究基础与存在的问题，结合所关注的关键科学和技术问题，介绍和分析了主要研究成果和进展，包括海域断裂活动性探测和地震构造、中国海域与邻区地震目录及地震活动特征、海域地震动特性及衰减模型、海域场地条件及对地震动的影响、海域地震区划图编制方法与技术等；编制了一系列相关图件、数据库和计算软件，包括中国东部和南部海域活动构造框架图、3个典型海域（位于黄海、台湾海峡、南海内）地震构造图、中国海域及邻区统一地震目录、中国海域潜在震源区划分图与考虑不确定性的对比方案及考虑三维潜源模型的地震危险性分析软件；建立了中国海域及邻区俯冲带地震构造模型、基于地震动观测记录和地震模拟数据的南海俯冲带板内地震动衰减关系、利用强震动加速度记录结合宽频带速度记录的俯冲带板缘与板内地震的地震动长周期反应谱衰减关系，提出了以场地覆盖土层厚度及土层等效剪切波速为指标的大陆架场地分类方法及相应的场地地震动参数调整方案；最后形成了海域地震区划图编制原则、技术要求和技术方法体系，完成了海域地震区划图编制规程（初稿）的编制工作，基本完成了3个典型海域地震区划图的编制工作。     

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.     

近断层竖向地震动峰值特征

为了研究近断层区域竖向地震动的加速度峰值衰减特征和竖向与水平加速度峰值比特征,为进行近断层区域结构抗震设计和地震危险性分析等提供基础数据参考,根据1952—1999年世界范围内震级在M5．4-M7．6之间的18次地震的地震动记录提出一种同时考虑断层距和震级影响的竖向峰值加速度衰减关系,并与其他学者提出的衰减关系进行了对比分析。然后初步统计分析了竖向与水平峰值加速度比值、竖向地震动PGV／PGA比值的特征。研究结果表明,本文提出的加速度峰值衰减关系形式比较简单而且能较好地体现地震动加速度峰值的衰减变化关系;断层距在0—40km范围内相当一部分竖向与水平向峰值加速度比值大于一般抗震设计规范中规定的比值即0．65;至少对于竖向地震动而言,只将PGV／PGA〉0．2s作为识别近断层脉冲型地震动的强度指标是不够的。     

基于华北区域地震活动性分布的地震危险性评价模型

采用了分布式地震活动性模型. 该模型无需潜在震源区划分,同时简化了地震危险性概率分析方法. 根据破坏性地震目录建立了3个地震活动性模型,利用高斯光滑函数获得了华北区域内的a值分布特征,使用3种典型的衰减模型,分别计算了50年内超越概率10%, 5%和2%的地震动峰值加速度分布. 其分析结果显示了峰值加速度分布特征与我国第四代区划图大体一致,特定地震活动区（太原、 石家庄等地区）的峰值加速度略高于第四代区划图的结果,而这种峰值加速度分布特征与该地区较高的地震活动性特征是一致的. 概率危险性曲线结果表明,唐山、太原和北京等地区的潜在地震危险性比华北区域内其它城市高.      

湖南地区分布式地震活动性模型在PSHA中的应用研究

本文采用了空间光滑地震活动性模型,该模型无需潜在震源区划分,同时发展了概率地震危险性分析新方法。根据三种地震目录资料建立了三种地震活动性模型,利用高斯光滑函数获得了湖南区域内的比值分布特征,使用了两种典型的衰减模型,计算了50年内超越概率10％的地震动峰值加速度（PGA）分布。其分析结果显示PGA分布特征与中国地震动参数区划图大体一致,部分区域PGA提高,PGA达0．05g的区域显著扩大,其中包括邵阳、湘潭、吉首、怀化等重要城市,而这种PGA分布特征与该地区地震活动性特征是一致的。概率危险性曲线的结果表明常德等地区的潜在地震危险性比湖南区域内其他城市高。表明此模型用于地震危险性计算中是简便易行的,且具有较高的精度。尤其对于地质和地震构造信息缺乏的弱震区和中强震区,该方法作为替代方法并有着广泛的应用价值。     

Probabilistic seismic hazard analysis in Nepal

The seismic ground motion hazard for Nepal has been estimated using a probabilistic approach. A catalogue of earthquakes has been compiled for Nepal and the surrounding region （latitude 26% N and 31.7% N and longitude 79° E and 90° E） from 1255 to 2011. The distribution of catalogued earthquakes, together with available geological and tectonic information were used to delineate twenty-three seismic source seismic source information and probabilistic earthquake hazard prediction relationship, peak ground accelerations （PGAs） have zones in Nepal and the surrounding region. By using the parameters in conjunction with a selected ground motion been calculated at bedrock level with 63%, 10%, and 2% probability of exceedance in 50 years. The estimated PGA values are in the range of 0.07-0.16 g, 0.21 0.62 g, and 0.38-1.1 g for 63%, 10%, and 2% probability of exceedance in 50 years, respectively. The resulting ground motion maps show different characteristics of PGA distribution, i.e., high hazard in the far-western and eastern sections, and low hazard in southern Nepal. The quantified PGA values at bedrock level provide information for microzonation studies in different parts of the country.     

Using Active Faults and Seismicity for the Strong Motion Modeling in the Eastern Rif (Northern Morocco)

— The aim of this study is to conduct a probabilistic seismic hazard analysis for the eastern Rif area in northern Morocco. The source zones were established on the basis of the seismicity database, the fracturing analysis deduced from Landsat7 ETM digital enhancement and marine seismic reflection profiles. By the use of this information together with the selected attenuation relationship, the peak ground acceleration contour maps are produced for specific return periods. The map has been divided into intervals of 0.1 degrees in both latitude and longitude to calculate the values at each grid point and draw the seismic hazard curves. The results of seismic hazard assessment are displayed as iso-acceleration contours expected to be exceeded during typical economic life times of structures.     

Application of Gumbel I and Monte Carlo methods to assess seismic hazard in and around Pakistan

A proper assessment of seismic hazard is of considerable importance in order to achieve suitable building construction criteria. This paper presents probabilistic seismic hazard assessment in and around Pakistan (23° N–39° N; 59° E–80° E) in terms of peak ground acceleration (PGA). Ground motion is calculated in terms of PGA for a return period of 475 years using a seismogenic-free zone method of Gumbel’s first asymptotic distribution of extreme values and Monte Carlo simulation. Appropriate attenuation relations of universal and local types have been used in this study. The results show that for many parts of Pakistan, the expected seismic hazard is relatively comparable with the level specified in the existing PGA maps.     

Seismic hazard map of the Middle East

The collaborative project Earthquake Model of the Middle East (EMME, 2010–2015) brought together scientists and engineers from the leading research institutions in the region and delivered state-of-the-art seismic hazard assessment covering Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Iraq, Jordan, Lebanon, Palestine, Pakistan, Syria and Turkey. Their efforts have been materialized in the first homogenized seismic hazard model comprising earthquake catalogues, mapped active faults, strong motions databank, ground motion models and the estimated ground motion values for various intensity measure types and relevant return periods (e.g. 475–5000 years). The reference seismic hazard map of the Middle East, depicts the mean values of peak ground acceleration with a 10% chance of exceedance in 50 years, corresponding to a mean return period of 475 years. A full resolution poster is provided with this contribution.     

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.     

Seismic hazard assessment for Cyprus

In the present study, probabilistic seismic hazard assessment was conducted for Cyprus based on several new results: a new comprehensive earthquake catalog, seismic source models based on new research, and new attenuation relationships. Peak ground acceleration distributions obtained for a return period of 475 years for rock conditions indicate high hazard along the southern coastline of Cyprus, where the expected ground motion is between 0.3 and 0.4 g. The rest of the island is characterized by values representing less severe shaking. Results of this study strongly indicate the inadequacy of the Turkish Earthquake Code that is being used in the northern part of the island and the Eurocode 8 that is in effect in the southern part of the island to approximate the uniform hazard spectra developed for the high hazard and moderate hazard regions of the island.     

An engineering prediction model of acceleration response spectra and its application to seismic hazard mapping

A regression analysis was made on 277 acceleration response spectra computed from Japanese accelerograms by subdividing the data into discrete categories. Five magnitude and distance categories, and four ground condition categories were used. The maximum absolute acceleration amplitude is predicted as a product of three factors, each representing a weighting factor for magnitude, distance and ground condition category at each of the 18 response spectrum periods from 0·1 s to 4 s at a damping value of 5 per cent of critical. A method was then developed to evaluate seismic hazard in terms of acceleration response spectrum by using the prediction model and the seismicity data, and it was applied to obtain seismic macro-zoning maps of Japan which are dependent on the natural period of a structure. The results of the analysis indicated that a single seismic zoning map may not be sufficient to cover a variety of structures with a wide range of periods because the expected spectral shape differs according to the seismicity of the area.     

Probabilistic seismic hazard assessment for the two layer fault system of Antalya (SW Turkey) area

Southwest Turkey, along Mediterranean coast, is prone to large earthquakes resulting from subduction of the African plate under the Eurasian plate and shallow crustal faults. Maximum observed magnitude of subduction earthquakes is Mw = 6.5 whereas that of crustal earthquakes is Mw = 6.6. Crustal earthquakes are sourced from faults which are related with Isparta Angle and Cyprus Arc tectonic structures. The primary goal of this study is to assess seismic hazard for Antalya area (SW Turkey) using a probabilistic approach. A new earthquake catalog for Antalya area, with unified moment magnitude scale, was prepared in the scope of the study. Seismicity of the area has been evaluated by the Gutenberg-Richter recurrence relationship. For hazard computation, CRISIS2007 software was used following the standard Cornell-McGuire methodology. Attenuation model developed by Youngs et al. Seismol Res Lett 68(1):58–73, (1997) was used for deep subduction earthquakes and Chiou and Youngs Earthq Spectra 24(1):173–215, (2008) model was used for shallow crustal earthquakes. A seismic hazard map was developed for peak ground acceleration and for rock ground with a hazard level of a 10% probability of exceedance in 50 years. Results of the study show that peak ground acceleration values on bedrock change between 0.215 and 0.23 g in the center of Antalya.     

A probabilistic seismic hazard assessment for the Turkish territory: part II—fault source and background seismicity model

Over the years, several local and regional seismic hazard studies have been conducted for the estimation of the seismic hazard in Turkey using different statistical processing tools for instrumental and historical earthquake data and modeling the geologic and tectonic characteristics of the region. Recently developed techniques, increased knowledge and improved databases brought the necessity to review the national active fault database and the compiled earthquake catalogue for the development of a national earthquake hazard map. A national earthquake strategy and action plan were conceived and accordingly with the collaboration of the several institutions and expert researchers, the Revision of Turkish Seismic Hazard Map Project (UDAP-Ç-13-06) was initiated, and finalized at the end of 2014. The scope of the project was confined to the revision of current national seismic hazard map, using the state of the art technologies and knowledge of the active fault, earthquake database, and ground motion prediction equations. The following two seismic source zonation models are developed for the probabilistic earthquake hazard analysis: (1) Area source model, (2) Fault and spatial smoothing seismic source model (FSBCK). In this study, we focus on the development and the characterization of the Fault Source model, the background spatially smoothed seismicity model and intrinsic uncertainty on the earthquake occurrence-rates-estimation. Finally, PSHA results obtained from the fault and spatial smoothed seismic source model are presented for 43, 72, 475 and 2475 years return periods (corresponding to 69, 50, 10, and 2% probability of exceedance in 50 years) for PGA and 5% damped spectral accelerations at 0.2 and 1.0 s.     

Seismic hazard assessment for Iceland in terms of macroseismic intensity using a site approach

We present the results of probabilistic seismic hazard assessment for Iceland in the framework of the EU project UPStrat-MAFA using the so-called site approach implemented in the SASHA computational code. This approach estimates seismic hazard in terms of macroseismic intensity by basically relying on local information about documented effects of past seismic events in the framework of a formally coherent and complete treatment of intensity data. In the case of Iceland, due to the lack of observed intensities for past earthquakes, local seismic histories were built using indirect macroseismic estimates deduced from epicentral information through an empirical attenuation relationship in probabilistic form. Seismic hazard was computed for four exceedance probabilities for an exposure time of 50 years, equivalent to average return periods of 50, 200, 475 and 975 years. For some localities, further return periods were examined and deaggregation analysis was performed. Results appear significantly different from previous seismic hazard maps, though just a semi-qualitative comparison is possible because of the different shaking measure considered (peak ground acceleration versus intensity), and the different computational methodology and input data used in these studies.     

Seismic hazard in southern Calabria (Italy) based on the analysis of a synthetic earthquake catalog

The application of a newly developed physics-based earthquake simulator to the active faults inferred by aeromagnetism in southern Calabria has produced a synthetic catalog lasting 100 ky including more than 18,000 earthquakes of magnitude ≥?4.0. This catalog exhibits temporal, spatial and magnitude features, which resemble those of the observed seismicity. As an example of the potential use of synthetic catalogs, a map of the peak ground acceleration (PGA) for a given exceedance probability on the territory under investigation has been produced by means of a simple attenuation law applied to all the events reported in the synthetic catalog. This map was compared with the existing hazard map that is presently used in the national seismic building regulations. The comparison supports a strong similarity of our results with the values given in the present Italian seismic building code, despite the latter being based on a different methodology. The same similarity cannot be recognized for the comparison of our present study with the results obtained from a previous study based on our same methodology but with a different geological model.     

Seismic hazard assessment using intensity point data

The influence of the attenuation model used in seismic hazard assessment in terms of intensity and acceleration is studied. For two sites in central Italy, the catalogue of the actual observed intensities during the last three centuries has been recovered. In the study region, the data collected during a recent seismic sequence give the basis for relating intensity and acceleration. The results show the importance of establishing statistical relationships among the used quantities, based on a representative set of data.     

"Parametric-historic" Procedure for Probabilistic Seismic Hazard Analysis Part II: Assessment of Seismic Hazard at Specified Site

—A new methodology for probabilistic seismic hazard analysis is described. The approach combines the best features of the "deductive" (Cornell, 1968) and "historic" (Veneziano et al., 1984) procedures. It can be called a "parametric-historic" procedure. The maximum regional magnitude mmax is of paramount importance in this approach and Part I of the authors’ work (Kijko and Graham, 1998) was dedicated to developing efficient statistical procedures that can be used for the evaluation of this parameter. In Part II the approach of a probabilistic seismic hazard assessment at a given site is described. The approach permits the utilization of incomplete earthquake catalogues. It is assumed that a typical catalogue contains two types of information historical macroseismic events that occurred over a period of a few hundred years and recent, instrumental data. The historical part of the catalogue contains only the strongest events, whereas the complete part can be divided into several subcatalogues, each assumed complete above a specified threshold of magnitude. The author’s approach also takes into account uncertainty in the determination of the earthquake magnitude. The technique has been developed specifically for the estimation of seismic hazard at individual sites, without the subjective judgment involved in the definition of seismic source zones, in which specific active faults have not been mapped and identified, and where the causes of seismicity are not well understood. As an example of the application of the new technique, the results of a typical hazard analysis for a hypothetical engineering structure located in the territory of South Africa are presented. It was assumed that the only reliable information in the assessment of the seismic hazard parameters in the vicinity of the selected site comes from a knowledge of past seismicity. The procedure was applied to seismic data that were divided into an incomplete part, containing only the largest events, and two complete parts, containing information obtained from instruments. The simulation experiments described in Part I of our study have shown that the Bayesian estimator K-S-B tends to perform very well, especially in the presence of inevitable deviations from the simple Gutenberg–Richter model. In the light of this fact value &gif1; = 6.66 - 0.44, which was obtained from the K-S-B technique, was regarded as the best choice. At an exceedance probability of 10^х per annum, the median value of peak ground acceleration on rock at the site is 0.31g, and at an exceedance probability of 10^ц per annum, the median peak ground acceleration at the site is 0.39g. The median value of the maximum possible acceleration at the site is 0.40g, which was calculated from attenuation formulae by assuming the occurrence of the strongest possible earthquake, e.g., with magnitude &gif1; = 6.66 at distance 10 km.     

Probabilistic seismic hazard assessment for Thailand

A set of probabilistic seismic hazard maps for Thailand has been derived using procedures developed for the latest US National Seismic Hazard Maps. In contrast to earlier hazard maps for this region, which are mostly computed using seismic source zone delineations, the presented maps are based on the combination of smoothed gridded seismicity, crustal-fault, and subduction source models. Thailand’s composite earthquake catalogue is revisited and expanded, covering a study area limited by 0°–30°N Latitude and 88°–110°E Longitude and the instrumental period from 1912 to 2007. The long-term slip rates and estimates of earthquake size from paleoseismological studies are incorporated through a crustal fault source model. Furthermore, the subduction source model is used to model the megathrust Sunda subduction zones, with variable characteristics along the strike of the faults. Epistemic uncertainty is taken into consideration by the logic tree framework incorporating basic quantities, such as different source modelling, maximum cut-off magnitudes and ground motion prediction equations. The ground motion hazard map is presented over a 10 km grid in terms of peak ground acceleration and spectral acceleration at 0.2, 1.0, and 2.0 undamped natural periods and a 5% critical damping ratio for 10 and 2% probabilities of exceedance in 50 years. The presented maps give expected ground motions that are based on more extensive data sources than applied in the development of previous maps. The main findings are that northern and western Thailand are subjected to the highest hazard. The largest contributors to short- and long-period ground motion hazard in the Bangkok region are from the nearby active faults and Sunda subduction zones, respectively.