Mapeamento das acelerações sísmicas do Estado do Ceará

Abstract

Seismicity in Brazil is considered low, not null, although many believe in the total absence of this threat, there are Brazilian regions that present a considerable frequency of events, few of which are earthquakes of high magnitude, which did not have disastrous consequences for having occurred in sparsely populated places. NBR 15421: 2006 establishes the procedures for the quantification of the seismic actions to be considered in the project and the requirements for the verification of the safety of the structures. This work presents a review on some basic concepts of seismology, on the main determinations of NBR 15421: 2006 for seismic analysis in buildings in the Brazilian territory. Where the main objective of this work is to determine the characteristic seismic acceleration, for that it was made the use of geoprocessing tools, executing an interpolation process for points limited by intensity zones, resulting in the seismic Microzoning map present in Annex B. We sought to develop a methodology of easy replication in order to carry out this determination for large territorial ranges and several target points. In this work, this methodology was applied for the state of Ceará, classifying the 184 municipalities in 3 different zones, zone 0, 1 and 2. Most of the municipalities are located in zone 1 whose seismic acceleration varies from 0.025g to 0.05g. At the end of the process, a database was created that uses the values found for seismic acceleration and the main parameters that make up the response spectrum. A numerical example is performed with a hypothetical building located in the municipality of Aracati, located at the limit between zone 1 and 2, thus carrying out the analysis to determine the seismic force by two different methods, following the recommendations of NBR 15421: 2006. Followed by a discussion on the seismic hazard map provided by NBR 15421: 2006, comparing the distribution of seismic events in Brazil with the map, and similarly performing this analysis for the state of Ceará. Noting that there are regions that do not have any analysis requirements, but have a high frequency of seismic records, for Ceará it occurs in a similar way, which has an analysis recommendation, however the delimitations used do not encompass a significant portion of unicipalities that present a history of equal or greater recurrence. In particular, we can mention the North Coast Region of the state and the Sertão de Sobral region, thus delimiting a range of coverage that exceeds the limits imposed by the seismic hazard map.