Aplicação de levantamentos aeromagnéticos na caracterização de falhas sismogênicas no Nordeste do Brasil

Abstract

The present research includes the integration of geophysical, seismological and geological data in the Northern domain of Borborema Province, Northeast of Brazil. This region presents areas with important records of neotectonic activities, and is seen as one of the most seismically active areas in the intraplate region of South America. The definitions in detail of the region and on which structures have been reactivated are still reasons for debate. The main aim of this study is to investigate the correlation between seismicity and the fabric of the Precambrian crystalline basement for the epicentral area of the Riacho Fundo and Samambaia faults. The faults present E-W and NE-SW trend, respectively, and exhibit a dextral transcurrent kinematics. The magnetic data were processed using the most varied filter applications in order to find the one that best correlated to contribute to the investigation of the reactivation of the basement fabric. Our investigation showed a correlation between the crystalline basement fabric and seismicity, which was done by comparing seismicity with interpreted magnetic lineaments. In the area of the Riacho Fundo fault, Granite Meruoca, the ductile fabric pattern indicates that the regional foliation is E-W-trending, correlating with the orientation of the epicenters zone. In the Samambaia fault region, the analysis of the basement fabric indicates that the regional foliation is NE-SW-trending, which coincides with the orientation of the epicenters and the quartz-chalcedony veins. In addition, in both regions, filters were applied to find the possible depths of the magnetic sources, associated with the faults and correlated with the regional hypocenters zone. With the Matched Filter, for the area of the Riacho Fundo fault we can obtain four depths: Deep ~ 2.7 - 7.2 km, Intermediate (1) ~ 1.2 - 2.6 km, Intermediate (2) ~ 0.4 - 1.1 km and Shallow ~ 0.0 - 0.3 km; the same was done for the area of the Samambaia fault, the four depths found for the magnetic sources were: Deep ~ 2.4 - 7.5 km, Intermediate (1) ~ 0.6 - 2.3 km, Intermediate (2) ~ 0.3 - 0.5 km, and Shallow ~ 0.0 - 0.2 km. Based on these data, we can observe that this relationship may indicate a reactivation of structures and the preexisting fabric for both areas.