Analysis of input data and seismic hazard assessment for the low seismicity area ‘Belgium,The Netherlands and NW Germany’

From the earthquake catalogue of the region of interest 2–8°E, 49–52°N, only events with intensity > 3 are considered. The fore/aftershocks and the induced seismicity are removed. The completeness and other properties of the remaining data set are investigated. The seismic data, as well as the geological, tectonic, and other geophysical data of the area are used for the determination of the seismotectonic zones. For each zone, the cumulative intensity-frequency relation (taking into account the completeness of the catalogue), the attenuation depending on the direction, the upper bound of intensity and the average depth are calculated. When the seismic activity is changing within a zone, this zone is divided into subzones with an almost constant activity and a b value equal to the value of the whole zone. When necessary for each subzone, a different attenuation coefficient can be used, to take into account more regional effects. Then the seismic hazard is assessed with the modified McGuire program. Annual probability versus intensity for several sites and hazard intensity and probability maps are calculated. Finally, an error discussion of the whole procedure for one test site is given.     

Seismic hazard in Northern Algeria using spatially smoothed seismicity. Results for peak ground acceleration

Seismic hazard in terms of peak ground acceleration (PGA) has been evaluated in northern Algeria using spatially smoothed seismicity data. We present here a preliminary seismic zoning in northern Algeria as derived from the obtained results.Initially, we have compiled an earthquake catalog of the region taking data from several agencies. Afterwards, we have delimited seismic areas where the b and m_max parameters are different. Finally, by applying the methodology proposed by Frankel [Seismol. Res. Lett. 66 (1995) 8], and using four complete and Poissonian seismicity models, we are able to compute the seismic hazard maps in terms of PGA with 39.3% and 10% probability of exceedance in 50 years.A significant result of this work is the observation of mean PGA values of the order of 0.20 and 0.45 g, for return periods of 100 and 475 years, respectively, in the central area of the Tell Atlas.     

Local seismic hazard assessment in areas of weak to moderate seismicity—case study from Eastern Germany

Generally the seismic hazard of an area of interest is considered independent of time. However, its seismic risk or vulnerability, respectively, increases with the population and developing state of economy of the area. Therefore, many areas of moderate seismic hazard gain increasing importance with respect to seismic hazard and risk analysis. However, these areas mostly have a weak earthquake database, i.e., they are characterised by relative low seismicity and uncertain information concerning historical earthquakes. In a case study for Eastern Thuringia (Germany), acting as example for similar places in the world, seismic hazard is estimated using the probabilistic approach. Because of the lack of earthquakes occurring in the recent past, mainly historical earthquakes have to be used. But for these the actual earthquake sources or active faults, needed for the analysis, are imprecisely known. Therefore, the earthquake locations are represented by areal sources, a common practice. The definition of these sources is performed carefully, because their geometrical shape and size (apart from the earthquake occurrence model) influence the results significantly. Using analysis tools such as density maps of earthquake epicentres, seismic strain and energy release support this. Oversizing of areal sources leads to underestimation of seismic hazard and should therefore be avoided. Large location errors of historical earthquakes on the other hand are represented by several alternative areal sources with final superimposition of the different results. In a very similar way information known from macroseismic observations interpreted as source rather than as site effects are taken into account in order to achieve a seismic hazard assessment as realistic as possible. In very local cases the meaning of source effects exceeds those of site effects very likely. The influence of attenuation parameter variations on the result of estimated local seismic hazard is relatively low. Generally, the results obtained by the seismic hazard assessment coincide well with macroseismic observations from the thoroughly investigated largest earthquake in the region.     

Comparison of two methods for seismic hazard assessment in a low-seismicity area

The EGO method, developed by Egozcue et al. and the SRAMSC method, originally developed by Cornell and later programmed by McGuire, to assess the seismic hazard, are compared for the low seismicity area Belgium, The Netherlands, and NW Germany. Using the same input data, the results of the EGO method without the majority criterion and the SRAMSC method with upper bound XII agree very well. The influence of the zoning is investigated for the EGO method. It is not necessary to define the zones for the EGO method so strictly as for the SRAMSC method, but too wide zones can give bad results.     

Tectonic stress,seismicity, and seismic hazard in the southeastern Carpathians

Intermediate-depth earthquakes in the Vrancea region occur in response to stress generation due to descending lithosphere beneath the southeastern Carpathians. In this article, tectonic stress and seismicity are analyzed in the region on the basis of a vast body of observations. We show a correlation between the location of intermediate-depth earthquakes and the predicted localization of maximum shear stress in the lithosphere. A probabilistic seismic hazard assessment (PSHA) for the region is presented in terms of various ground motion parameters on the utilization of Fourier amplitude spectra used in engineering practice and risk assessment (peak ground acceleration, response spectra amplitude, and seismic intensity). We review the PSHA carried out in the region, and present new PSHA results for the eastern and southern parts of Romania. Our seismic hazard assessment is based on the information about the features of earthquake ground motion excitation, seismic wave propagation (attenuation), and site effect in the region. Spectral models and characteristics of site-response on earthquake ground motions are obtained from the regional ground motion data including several hundred records of small and large earthquakes. Results of the probabilistic seismic hazard assessment are consistent with the features of observed earthquake effects in the southeastern Carpathians and show that geological factors play an important part in the distribution of the earthquake ground motion parameters.     

Pathways to seismic hazard evaluation: Extreme and characteristic earthquakes in areas of low and high seismicity

The general philosophy of seismic hazard evaluation described here is appropriate for selection of seismic input to regional earthquake engineering codes prior to detailed on-site inspections and geotechnical assessments. Some probabilistic seismic hazard methodologies which can be applied in areas of low and high seismicity, are briefly described to emphasise the main equations with specimen results. Three aspects of hazard assessment are explored by different pathways. These include the analysis of regional earthquake catalogues to obtain magnitude recurrence, particularly using Gumbel extreme value statistics. This is extended to assess ground shaking hazard which is usually sought by earthquake engineers. Thirdly, the concept of earthquake perceptibility is developed, leading to the identification of an earthquake magnitude or type which is characteristic of a region. This most perceptible earthquake is most likely to be felt at any site in a region and provides an earthquake selection criterion which can be used in aseismic design of noncritical structures. Because there are several methods of seismic hazard evaluation, the view is expressed that it is sensible for practical purposes to seek results from different methods or different pathways to the hazard evaluation.Paper presented at the Commission of the European Communities' School on Earthquake Hazard Evaluation, Athens, and at the 21st General Assembly of the European Seismological Commission, held in Sofia, 1988.Now at School of Environmental Sciences, University of East Anglia, University Plain, Norwich NR4 7TJ, U.K.     

Probabilistic assessment of seismic hazard of dam sites in Jordan

A Probabilistic method is used to evaluate the seismic hazard of nineteen embankment dam sites in Jordan. A line source model developed by McGuire (1978) is used in this study. An updated earthquake catalogue covering the period from 1 A.D. to 1991 A.D. is used for this purpose. This catalogue includes all earthquakes that occurred in Jordan and adjacent areas, more specifically between latitudes 27.0°–35.5° N and longitudes 32.0°–39.0° E.Nine distinct seismic sources of potential seismic activities are identified. The seismic hazard parameters are determined using the method suggested by Kijko and Sellevoll (1989).The Peak Ground Acceleration (PGA) is selected as a measure of ground motion severity. Esteva (1974) attenuation relationship is used in evaluating PGA values at each dam site. Analysis is carried out for 50%, 90%, and 95% probability that is not being exceeded in a life time of 50, 100, and 200 years.Results of analysis indicate that PGA values are higher for dam sites closer to the Dead Sea Fault. This fault is believed to be responsible for most earthquake activities in Jordan and vicinity. The highest PGA value is found to be for Al-Karama dam site.     

The importance of paleoseismology in seismic hazard studies for critical facilities

This paper is intended to provide a perspective on the use of paleoseismological studies in the seismic hazard assessment of critical facilities, such as dams, chemical/petrochemical facilities and nuclear power plants. In particular, the use of data obtained from paleoseismological studies for probabilistic seismic hazard analyses, when the required probabilities of exceedance are very low (e.g. 10^{− 6}–10^{− 7}) is considered. Recent revisions to the IAEA Safety Standards that provide guidance to Member States in their work related to the seismic safety of nuclear power plants are presented to illustrate the importance of this emerging discipline.     

Fuzzy-based method for landslide hazard assessment in active seismic zone of Himalaya

Landslides in Himalaya cause widespread damage in terms of property and human lives. It the present study, an attempt is made to derive information on causative parameters and preparation of landslide-susceptible map using fuzzy data integration in one of the seismically active region of Garhwal Himalaya that was recently devastated by a huge landslide. High-resolution remotely sensed data products acquired from Indian Remote Sensing Satellite before and after the landslide event were processed to improve interpretability and derivation of causative parameters. Spatial data sets such as lithology, rock weathering, geomorphology, lineaments, drainage, land use, anthropogenic factor, soil type and depth, slope gradient, and slope aspect were integrated using fuzzy gamma operator. The final map was reclassified in to five classes such as highly to lowly susceptible classes based on cumulative cutoff. The result shows around 72% of known landslide areas including the large Uttarkashi landslide in the high and very high susceptibility classes comprising of only 37% of the total area. The precipitation data from ground- and satellite-based observations were compared; the precipitation threshold and the role of seismic activity were analyzed for initiation of landslide.     

Seismic hazard computations for regions with low earthquake activity — A case study for the Belgium,The Netherlands and NW Germany area

The algorithms to evaluate seismic hazard, used and/or developed by five teams participating in the TERESA project, applied to the low seismicity area Belgium, The Netherlands and NW Germany are compared. The main differences in the results can be explained by the majority criterion of Egozcue et al. (1989), the differences in the upper bound and zonification and, in some cases, by a higher attenuation.     

Seismic hazard studies for Gaziantep city in South Anatolia of Turkey

Seismic hazard studies were conducted for Gaziantep city in the South Anatolia of Turkey. For this purpose, a new attenuation relationship was developed using the data of Zaré and Bard and accelerations were predicted employing this new equation. Deterministic approach, total probability theorem and GIS methodology were all together utilized for the seismic assessments. Seismic hazard maps with 0.25° grid intervals considering the site conditions were produced by the GIS technique. The results indicated that the acceleration values by the GIS hazard modelings were matched with the ones from the deterministic approach, however, they were underestimated comparing with the total probability theorem. In addition, the GIS based seismic hazard maps showed that the current seismic map of Turkey fairly yields conservative acceleration values for the Gaziantep region. Therefore, the constructed GIS hazard models are offered as a base map for a further modification of the current seismic hazard map.     

Critical parameter investigation for earthquake hazard assessment in the Sannio-Matese area of Southern Italy

Probabilistic methods have been applied for the assessment of seismic hazard in a selected region of Southern Italy (Sannio-Matese). This method is mainly suitable for engineering and planning purposes and was first introduced in 1968 by Cornell and efficiently codified into a FORTRAN computer program by McGuire. Special attention is paid in this paper to the specific input parameters, i.e. completeness of data catalogues, time variability of seismic activity, different forms of frequency distributions, and regional attenuation characteristics.     

Hazard assessment and runout analysis for an unstable rock slope above an industrial site in the Riviera valley, Switzerland

This paper presents a detailed field investigation and hazard assessment for an unstable rock slope above an industrial site in the Riviera valley in the Canton of Ticino in southern Switzerland. An integrated framework was used to counter issues of geological complexity and uncertainty, linking geological mapping and numerical modeling to develop an understanding of the acting instability mechanism to 2-D and 3-D dynamic runout simulations to predict the travel path and reach in the event of a large volume rockslide. The results from the numerical stability analysis provided a means to constrain failure volume estimates, whereas a series of calibration simulations were used to constrain the input parameters required by the rheological model used for the runout analysis. Results from this assessment suggest that current protection measures in place may not be sufficient, helping local authorities to define hazard zones and aid further development plans for the region.     

An estimate of probabilistic seismic hazard for five cities in Greece by using the parametric-historic procedure

A probabilistic procedure was applied to assess seismic hazard for the sites of five Greek cities (Athens, Heraklion, Patras, Thessaloniki and Volos) using peak ground acceleration as the hazard parameter. The methodology allows the use of either historical or instrumental data, or a combination of both. It has been developed specifically for the estimation of seismic hazard at a given site and does not require any specification of seismic sources or/and seismic zones. A new relation for the attenuation of peak ground acceleration was employed for the shallow seismicity in Greece. The computations involved the area- and site-specific parts. When assessing magnitude recurrence for the areas surrounding the five cities, the maximum magnitude, m_max, was estimated using a recently derived equation. The site-specific results were expressed as probabilities that a given peak ground acceleration value will be exceeded at least once during a time interval of 1, 50 and 100 years at the sites of the cities. They were based on the maximum peak ground acceleration values computed by assuming the occurrence of the strongest possible earthquake (of magnitude m_max) at a very short distance from the site and using the mean value obtained with the help of the attenuation law. This gave 0.24 g for Athens, 0.53 g for Heraklion (shallow) and 0.39 g Heraklion (intermediate-depth seismicity), 0.30 g for Patras, 0.35 g for Thessaloniki and 0.30 g for Volos. In addition, the probabilities of exceedance of the estimated maximum peak ground acceleration values were calculated for the sites. The standard deviation of the new Greek attenuation law demonstrates the uncertainty and large variation of predicted peak ground acceleration values.     

泥石流危险度野外快速评价方法探讨

文章系统地总结和分析了当前比较常用的泥石流危险度评价的研究方法,指出现行泥石流危险度评价中评价因子的提取往往需要详细野外勘查,工作量大、费用高,不便于对众多泥石流沟的普查;并提出一种在现场踏勘基础上,基于泥石流规模、频率和承灾体特征的快速便捷的新方法——泥石流危险度野外快速评价,并结合其他方法进行了实例对比验证。结果表明：泥石流危险度野外快速评价结果可靠,可作为快速评价泥石流危险性的新方法进行推广应用。     

陕西宝鸡地区胡家山滑坡风险性评价

在综合分析国内外滑坡风险评价方法的基础上,通过对野外地质灾害的调查、对胡家山滑坡的勘查和岩土物理力学参数的测试分析,利用Geo-slope软件和经验方法对滑坡多级潜在滑面进行稳定性分析、影响范围预测和失稳概率分析,开展了对滑坡在天然状态、10年一遇降雨和50年一遇降雨3种工况条件下的危险性、承灾体易损性分析等,完成了胡家山滑坡风险性评价,探讨了单体滑坡风险评价的技术方法与流程。根据评价结果,胡家山滑坡财产最大风险为113.71万元/年,人口最大风险为0.0648人/年,其人口风险超过了社会可容许的风险标准。因此,应采取加强监测、搬迁避让、适当工程治理等方法进行风险控制,以达到防灾减灾的目的。     

陕西宝鸡地区胡家山滑坡风险性评价

在综合分析国内外滑坡风险评价方法的基础上,通过对野外地质灾害的调查、对胡家山滑坡的勘查和岩土物理力学参数的测试分析,利用Geo-slope软件和经验方法对滑坡多级潜在滑面进行稳定性分析、影响范围预测和失稳概率分析,开展了对滑坡在天然状态、10年一遇降雨和50年一遇降雨3种工况条件下的危险性、承灾体易损性分析等,完成了胡家山滑坡风险性评价,探讨了单体滑坡风险评价的技术方法与流程。根据评价结果,胡家山滑坡财产最大风险为113.71万元/年,人口最大风险为0.0648人/年,其人口风险超过了社会可容许的风险标准。因此,应采取加强监测、搬迁避让、适当工程治理等方法进行风险控制,以达到防灾减灾的目的。     

Influence of slow active faults in probabilistic seismic hazard assessment: the northwestern margin of the València trough

Areas of low strain rate are typically characterized by low to moderate seismicity. The earthquake catalogs for these regions do not usually include large earthquakes because of their long recurrence periods. In cases where the recurrence period of large earthquakes is much longer than the catalog time span, probabilistic seismic hazard is underestimated. The information provided by geological and paleo-seismological studies can potentially improve seismic hazard estimation through renewal models, which assume characteristic earthquakes. In this work, we compare the differences produced when active faults in the northwestern margin of the València trough are introduced in hazard analysis. The differences between the models demonstrate that the introduction of faults in zones characterized by low seismic activity can give rise to significant changes in the hazard values and location. The earthquake and fault seismic parameters (recurrence interval, segmentation or fault length that controls the maximum magnitude earthquake and time elapsed since the last event or T_e) were studied to ascertain their effect on the final hazard results. The most critical parameter is the recurrence interval, where shorter recurrences produce higher hazard values. The next most important parameter is the fault segmentation. Higher hazard values are obtained when the fault has segments capable of producing big earthquakes. Finally, the least critical parameter is the time elapsed since the last event (T_e), when longer T_e produces higher hazard values.     

公路沿线花岗岩风化区滑坡危险度评价--以日本49号国道合户地区为例

对公路沿线边坡进行稳定性评价及滑坡灾害分析，对于由滑坡、泥石流等引起的公路灾害的防治具有重要指导意义。为了评价处于花岗岩风化区的日本福岛县合户地区49号国道沿线边坡的滑坡危险程度，在调查和分析了该地区的表层破坏模式、并通过简易探测方法摸清了风化土层的厚度分布后，将研究区域划分为边坡单元(Slopeunit)，使用椭球体下半部模拟滑动面的形状，通过随机试算法确定各边坡单元危险滑动面的位置及空间形状；采用一种基于GIS的边坡稳定性三维分析模型计算各边坡单元最小安全系数以及滑坡发生概率，定量评价滑坡灾害危险程度。所有的计算过程及结果显示均在一个基于GIS平台的系统中完成，为如何利用GIS技术更好地为滑坡灾害防治工作服务拓宽了思路。