Made available in DSpace on 2015-03-13T17:08:31Z (GMT). No. of bitstreams: 1 CristianoAA_ ate_Cap2.pdf: 1327011 bytes, checksum: cfe873f3ff16b6f2815cd10726ecad9f (MD5) Previous issue date: 2000-06-30 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / This MSc thesis describes brittle deformation in two seismic zones located in north-eastern Brazil: Jo?o C?mara and S?o Rafael, Rio Grande do Norte State. Both areas show seismogenic faults, Samambaia and S?o Rafael, indicated by narrow zones of epicentres with a strike of 040o, a lenght of 30 km and 4 km, and a depth of 1-12 and 0,5-4 km, respectively. The first seismological and geological studies suggested blind faults or faults that were still in the beginning of the nucleation process. The region is under E-W-oriented compression and is underlain by Precambrian terrains, deformed by one or more orogenic cycles, which generated shear zones generally marked by strong pervasive foliation and sigmoidal shapes. The crystalline basement is capped by the Cretaceous Potiguar basin, which is also locally capped by Pliocene continental siliciclastic deposits (Barreiras Formation), and Quaternary alluvium. The main aim of this study was to map epicentral areas and find whether there are any surface geological or morphotectonic expression related to the seismogenic faults. A detailed geological map was carried out in both seismic areas in order to identify brittle structures and fault-related drainage/topographic features. Geological and morphotectonic evidence indicate that both seismogenic faults take place along dormant structures. They either cut Cenozoic rocks or show topographic expression, i.e., are related to topographic heights or depressions and straight river channels. Faults rocks in the Samambaia and S?o Rafael faults are cataclasite, fault breccia, fault gouge, pseudotachylyte, and quartz veins, which point to reactivation processes in different crustal levels. The age of the first Samambaia and the S?o Rafael faulting movement possibly ranges from late Precambrian to late Cretaceous. Both fault cut across Precambrian fabric. They also show evidence of brittle processes which took place between 4 and 12 km deep, which probably have not occurred in Cenozoic times. The findings are of great importance for regional seismic hazard. They indicate that fault zones are longer than previously suggested by seismogenic studies. According to the results, the methodology used during this thesis may also be useful in other neotectonic investigation in intraplate areas / Esta disserta??o de mestrado descreve a deforma??o r?ptil em duas zonas s?smicas no Nordeste do Brasil: Jo?o C?mara e S?o Rafael, estado do Rio Grande do Norte. Ambas as ?reas mostram falhas sismog?nicas, Samambaia e S?o Rafael, indicadas por zonas estreitas de epicentros com dire??o N40oE, comprimentos de 30 km e 4 km, e profundidades de 1-12 km e 0,5-4 km, respectivamente. Os primeiros estudos sismol?gicos e geol?gicos realizados nestas ?reas sugeriram tratar-se de falhas cegas ou ainda em processo de nuclea??o. A regi?o se encontra sob regime de compress?o com dire??o aproximadamente E-W e ? formada por um embasamento cristalino deformado por um ou mais ciclos orog?nicos, que geraram zonas de cisalhamento marcadas por folia??o forte e penetrativa e formas sigmoidais. O embasamento cristalino ? recoberto pela Bacia Potiguar, de idade Cret?cea, que tamb?m ? capeada por sedimentos continentais silicicl?sticos da Forma??o Barreiras e aluvi?es quatern?rios. O principal objetivo do presente trabalho foi mapear as ?reas epicentrais e descobrir se as mesmas apresentavam alguma fei??o geol?gica ou morfotect?nica relacionada ?s falhas sismog?nicas. Mapas geol?gicos de detalhe foram feitos em ambas as ?reas com o objetivo de identificar estruturas r?pteis e fei??es de drenagens ou topogr?ficas relacionadas com falhamentos. Evid?ncias geol?gicas e morfotect?nicas indicaram que ambas as falhas sismog?nicas ocorreram em estruturas pr?-existentes. As falhas cortam rochas cenoz?icas ou mostram express?o topogr?fica relacionada a altos/baixos de relevo e canais alinhados de rios. As rochas de falha nas falhas de Samambaia e S?o Rafael s?o cataclasitos, brechas de falha, gouge, pseudotaclito e veios de quartzo e calced?nia, que apontam para processos de reativa??o em diferentes n?veis crustais. A idade da primeira movimenta??o das falhas de Samambaia e S?o Rafael possivelmente varia entre o final do Pr?-Cambriano e o final do Cret?ceo. Ambas as falhas cortam o fabric Pr?-cambriano e mostram evid?ncias de processos fr?geis que ocorreram entre 4 e 12 km de profundidade, os quais provavelmente n?o aconteceram durante o Cenoz?ico. Os resultados s?o de grande import?ncia para o risco s?smico regional. Eles indicam que as falhas mapeadas pelo presente trabalho s?o mais longas que as falhas descritas pelos estudos sismol?gicos. A metodologia utilizada pelo presente estudo pode ter grande aplica??o em outras ?reas sismog?nicas intraplaca