AN ENGINEERING APPROACH FOR EVALUATING THE SEISMICRISK IN BRAZILIAN SOUTHEAST REGION

摘要

Brazilian Southeast region presents a low seismic activity, typical of an intra-plate region. Since thedesign of the first Brazilian Nuclear Power Plants, the study of the Brazilian seismicity, in a scientificbasis, has begun. An important seismographic network, presently in continuous operation, has beenimplemented in Brazil.The objective of this paper is to present an evaluation, considering an 'engineering approach', of theseismic risk in Brazilian Southeast region. The work is based upon the already available seismic data inthis region and also in the theoretical seismological studies already developed in this subject. Thecharacteristic of the adopted 'engineering approach' is, from the restricted amount of the availableseismological data, and through a simplified process, to obtain an evaluation of the probabilisticdistribution function of the horizontal ground accelerations in the analyzed site, in a reliable andconservative way. The concept of 'diffuse seismicity' is used in this evaluation, i. e., the seismic risk isnot evaluated from actual geological faults with a given seismic potential, but from sources diffuselydistributed on the considered Tectonic Province.The seismic risk is evaluated, in Brazilian Southeast, for two different types of structures, according totheir importance to the public safety: critical structures, such as Nuclear Power Plants and usualstructures, such as residential and commercial buildings. The importance of the analyzed structures isreflected in the reference probability levels to be considered in design of each of them.The importance of the seismic risk analysis in the discussed region is illustrated through a numericalexample, of a commercial building in the city of Rio de Janeiro, with height ranging between one and fiftyfloors, in which horizontal forces due to wind and due to earthquake are applied. The comparison betweenthe effects of these forces shows that, in some cases, seismic forces can be the dominant ones.