Abstract

A comprehensive and probabilistic seismic risk assessment has been performed for the buildings of Lorca, the most affected city in the region of Murcia, Spain, after the May 2011 earthquake. Seismic hazard is represented through a set of stochastic scenarios that allow accounting for small, moderate and extreme events in the future losses, also through spectral transfer functions the dynamic soil response has been considered. A building by building resolution level database has been used allowing the disaggregation of risk results in several categories besides allowing the generation of risk maps to visualize the geographical distribution of the future losses. For each of the identified building classes a vulnerability function has been assigned to determine the expected losses for different acceleration levels. Risk results have been obtained in terms of the loss exceedance curve from where other probabilistic risk metrics such as the average annual loss and the probable maximum loss can be derived. Risk results are useful for the decision-makers in the fields of emergency planning, existent building retrofitting schemes and financial protection through traditional insurance and reinsurance schemes or with alternative risk transfer instruments.

Abstract

Seismic hazard assessment is a basic tool for rational planning and designing in areas of different seismic activity. The Bayesian probability estimation was applied in this study to assess seismic hazard. The estimation procedure provides a posterior probability distribution that integrates prior estimates based on the knowledge of the process, and the likelihood of occurrence based on historical data. The Bayesian approach was applied to calculate the probability that a certain cut-off magnitude would be exceeded at certain time intervals in different regions of Iran. The results for the cut-off magnitude of 6.5 indicate that the highest probability of seismic hazard exists in the Alborz, Kopeh-Dagh, Bandar-Abas, Kerman, and Zagros regions. The seismic hazard is lowest for the Esfahan–Sirgan region, the Arabian Platform, the Persian Gulf, and Kavir in Central Iran. The comparison between the Bayesian results and the seismotectonic models of Iran reveals that it is possible to partition the spatially distributed epicenters of earthquake events into different regions. In general, these regional divisions agree with previously proposed seismotectonic provinces of Iran.

Abstract

This work attempts to explain how probabilistic seismic risk assessments can be performed at different resolution levels, using, strictly speaking, the same methodology (or arithmetic) and, then, how to obtain results in terms of the same metrics; but, also, highlighting what the differences in terms of inputs for the analysis and the reasons for them (i.e. including the dynamic soil response effects which are only relevant in local assessments) are. First, a country level assessment is first performed with similarities to the presented by Cardona et al. (2014) using a coarse-grain exposure database that includes only the building stock in the urban regions of Spain. Second, a urban seismic risk assessment with the detail of state-of-the-art studies such as the ones developed by Marulanda et al. (2013) and Salgado-Gálvez et al (2013; 2014a) is performed for Lorca, Murcia. In both cases, the fully probabilistic seismic risk results are expressed in terms of the loss exceedance curve which corresponds to the main output of said analysis from where different probabilistic risk metrics, such as the average annual loss and the probable maximum loss, as well as several other relationships, can be derived (Marulanda et al., 2008; Bernal, 2014). Because of the damage data availability for the Lorca May 2011 earthquake, a comparison between the observed losses and those modelled using an earthquake scenario with similar characteristics in terms of location, magnitude and spectral accelerations was done for the building stock of the city. The results of the comparison are presented in terms of expected losses (in monetary terms) and damage levels related to the obtained the mean damage ratios compared with the observed by post-earthquake surveys.

Abstract

In the present work, the main steps used in the probabilistic estimation of the seismic hazard of the city of Barcelona, ​​Spain, are described, and it is mentioned how the hazard was used in the probabilistic estimation of the seismic risk of the city. For comparative purposes, the seismic hazard of Barcelona was estimated both in terms of exceedance rate of the macroseismic intensities, and in terms of exceedance rate of the maximum ground acceleration (PGA). In the estimation, the computer code CRISIS2008 (Ordaz et al., 2008) was used, which is based on the methodology proposed by Cornell (1968) and Esteva (1970). This code incorporates valuable tools that allow estimates of seismic hazards to be made at an important level of detail. According to the results, in Barcelona, ​​the PGA value equal to 85 cm/s2, has an average return period of 475 years. The results obtained in terms of macroseismic intensities, indicate that the intensity that has an average a return period of 475 years corresponds to a value between VI and VII. The seismic hazard curves in terms of macroseismic exceedance rates were obtained with the aim of being used in the estimation of the seismic risk of the city by means of the probabilistic method of vulnerability indices (Aguilar, 2011). According to the results, in the city there are buildings with a high level of seismic risk. This is because, despite the fact that Barcelona is located in a zone of low to moderate seismicity, there is a significant percentage of buildings with significantly high levels of seismic vulnerability. The seismic risk curves obtained are expressed in terms of exceedance frequencies of the degrees of seismic damage.

Abstract

The vulnerability index method, in its version developed in the framework of the European project Risk-UE, has been adapted and applied in this article, to evaluate the seismic risk for the city of Barcelona (Spain) through a GIS based tool. According to this method, which defines five damage states, the action is expressed in terms of the macroseismic intensity and the seismic quality of the buildings by means of a vulnerability index. The probabilities of damage states are obtained considering a binomial or beta-equivalent probability distribution. The most relevant seismic risk evaluation results obtained, for current buildings and monuments of Barcelona, are given in the article as scenarios of expected losses.

Abstract

The seismic risk of the buildings of Barcelona, Spain, is analyzed by using a method based on the capacity spectrum. The seismic hazard in the area of the city is described by means of the reduced 5% damped elastic response spectrum. Obtaining fragility curves for the most important building types of an urban center requires an important amount of information about the structures and the use of nonlinear structural analysis tools. The information on the buildings of Barcelona was obtainedby collecting, arranging, improving, and completing the database of the housing and current buildings. The buildings existing in Barcelona are mainly of two types: unreinforced masonry structures and reinforced concrete buildings with waffled slab floors. In addition, the Arc-View software was used to create a GIS tool for managing the collected information to develop seismic risk scenarios. This study shows that the vulnerability of the buildings is significant and therefore, in spite of the medium to low seismic hazard in the area of the city, the expected seismic risk is considerable.

Abstract

Conceptual aspects related to seismic vulnerability, damage and risk evaluation are discussed first, together with a short review of the
most widely used possibilities for seismic evaluation of structures. The capacity spectrum method and the way of obtaining seismic
damage scenarios for urban areas starting from capacity and fragility curves are then discussed. The determination of capacity curves for buildings using non-linear structural analysis tools is then explained, together with a simplified expeditious procedure allowing the
development of fragility curves. The seismic risk of the buildings of Barcelona, Spain, is analyzed in the paper, based on the application of the capacity spectrum method. The seismic hazard in the area of the city is described by means of the reduced 5% damped elastic response spectrum. The information on the buildings was obtained by collecting, arranging, improving and completing a broad database of the dwellings and current buildings. The buildings existing in Barcelona are mainly of two types: unreinforced masonry structures and reinforced concrete buildings with waffled-slab floors. The ArcView software was used to create a GIS tool for managing the collected information in order to develop seismic risk scenarios. This study shows that the vulnerability of the buildings is significant in Barcelona and, therefore, in spite of the low-to-moderate seismic hazard in the region, the expected seismic risk is considerable.

Abstract

The present monograph is a continuation of the monograph MIS-10 and uses the same concepts and definitions described therein. However, to facilitate reading, the authors briefly describe some of the aforementioned concepts. The monograph is based on the definition of seismic risk based on the convolution of three factors: 1) the seismic hazard, which represents the probability of occurrence, within a specific period of time and a given area, of a seismic motion with a given intensity; 2) the seismic vulnerability of a structure or group of structures, defined as the degree of damage due to the occurrence of a seismic motion of a given intensity; 3) the cost of the structures. It is explained that the mechanism to reduce seismic risk is the reduction of vulnerability and, therefore, its evaluation is required. The main result of the risk studies is the expected loss (or the expected degree of damage) that a structure of a given typology would suffer due to the action of an earthquake of certain characteristics. This result can be described by means of damage probability matrices, or by vulnerability functions (relations that express, in a continuous way, the vulnerability according to a parameter that describes the size of the earthquake). The calculation, both of probability matrices of damage and of vulnerability functions, can be carried out, on the one hand, from statistical studies of data observed during past earthquakes or, on the other, by calculating the response of structures based on models.

Abstract

The design and construction of structures in seismic areas requires knowledge of the seismic actions to which they can be subjected throughout their useful life. In general, it is not enough to establish what would be the maximum acceleration which could act upon the structure to be designed, but, in addition, the frequency with which the seismic phenomenon occurs and the damage it would produce should be known. In this monograph the probability of occurrence of earthquakes is studied regardless of the type of structure, of the population of the area, of the industrial level of the same, for the northeast area of ​​the Iberian Peninsula; the results obtained are reflected in maps. The study is restricted to finding the probabilities of occurrence of earthquakes classified by their intensity (epicentral or felt) and, in spite of the approximation due to the use of the intensities, the results will be of great value for the making of design decisions. The methods for evaluating these probabilities of intensity occurrence are very varied, but basically there are two different conceptions of the methods of calculation: the deterministic methods and the probabilistic ones. The deterministic methods start from the recorded earthquakes and evaluate the effects of these using different coefficients. The probabilistic methods do not directly use the recorded earthquakes, but these data serve to establish certain laws of probability of occurrence that give rise to regional or zonal models of occurrence. The method presented herein has elements of both approaches, although always in the context of Bayesian statistics and is adapted to the special conditions of the northeast of the Iberian Peninsula or other areas where data are scarce and seismicity is moderate.

Abstract

This monograph presents the fundamental concepts related to seismic action, the structural response of buildings, the assessment of vulnerability, risk and seismic damage. Some indices proposed by different researchers are also indicated to assess the level of damage suffered by buildings under seismic actions. It also describes the ways to define the seismic action that are appropriate to the structural analysis. Techniques are developed to generate artificial accelerograms, which are necessary to perform the evaluation of the non-linear seismic response through an analysis in time. This evaluation also allows obtaining the level of damage suffered by the structures. The seismic action is focused on the city of Barcelona, ​​Spain, which is located in an area of moderate seismicity and, in addition, does not have seismic records. The seismic action is established by seismic design spectra and artificial accelerograms compatible with said spectra. At the end of this work, the responses spectra considered to define the seismic demand and the artificial accelerograms obtained are shown, which can be used for the evaluation of structures for different seismic intensities and for different locations in Barcelona. Finally, a methodology for assessing the vulnerability and the seismic risk of buildings is described. The methodology is applied in several steps and includes modeling and non-linear analysis of structures. It is focused on obtaining fragility curves, which can be generated both through an empirical evaluation and through an analytical evaluation. The first is based on the damage observed in the buildings of an area after an earthquake occurs, while the second is based on a numerical analysis, where the seismic response of the structure is predicted.