Seismogenic faulting in the Meruoca granite, NE Brazil, consistent with a local weak fracture zone

Abstract

A sequence of earthquakes occurred in 2008 in the Meruoca granitic pluton, located in the northwestern part of the Borborema Province, NE Brazil. A seismological study defined the seismic activity occurring along the seismically-defined Riacho Fundo fault, a 081° striking, 8 km deep structure. The objective of this study was to analyze the correlation between this seismic activity and geological structures in the Meruoca granite. We carried out geological mapping in the epicentral area, analyzed the mineralogy of fault rocks, and compared the seismically-defined Riacho Fundo fault with geological data. We concluded that the seismically-defined fault coincides with ~E-W-striking faults observed at outcrop scale and a swarm of Mesozoic basalt dikes. We propose that seismicity reactivated brittle structures in the Meruoca granite. Our study highlights the importance of geological mapping and mineralogical analysis in order to establish the relationships between geological structures and seismicity at a given area.

Structural framework of the Jaibaras Rift, Brazil, based on geophysical data

“…4d and 5d), which represent seismogenic zones (Oliveira et al, 2010;Moura, 2012;Moura et al, 2014). These features are also well observed on satellite images and in the topography.…”

“…The high values are consistent with its acid and potassium-rich nature (Dickson and Scott, 1997). A large number of earthquakes have been recorded in the Meruoca Granite area, between 2008 and 2010 (Oliveira et al, 2010;Moura, 2012;Moura et al, 2014). A more detailed geophysical/geological mapping was performed aiming at identifying areas more prone to earthquakes since percolation of fluids is expected to occur in faults and, hence, variation in the radionuclides contents.…”

“…Sykes (1978) and Boyce and Morris (2002) drew attention to the intraplate tectonics and revealed weakness zones in the continental crust, in rift basin regions with deep faults, as is also the case of the Jaibaras Basin that could be reactivated by stress generated at some distance from plate boundaries. Indeed, the geophysical data interpretation based on lineaments, geophysical fields, and modeling allowed identifying potential areas for the occurrence of earthquakes in the region (Oliveira et al, 2010;Moura, 2012;Moura et al, 2014).…”

Sismicidade na Zona Sísmica Acaraú, região nordeste do Brasil, entre 2008 e 2018

“…No Local 3, os hipocentros mais rasos estão a 8 km, os mais profundos a 9 km e o mecanismo focal mostrou falhamento normal (Menezes, 2017). A orientação da Falha Riacho coincide com as anomalias magnéticas no granito Meruoca e em seu embasamento (Moura et al, 2014). Há poucos casos como esse no mundo, como exemplo, na falha Hosgri, na costa central da California (Hardbeck, 2010) e na sismicidade de Caraíbas-Itacambi, em Minas Gerais (Chimpliganond et al, 2010).…”

“…Apesar dessa proximidade, não podemos afirmar que a sismicadade da ZSA nos últimos 10 anos, ocorreu devido à uma possível reativação do Lineamento Transbrasiliano. É muito difícil encontrar correlação entre sismicidade e reativações de zonas de cisalhamento, especialmente com o Lineamento Transbrasiliano (Oliveira et al, (2010); Moura et al, (2014)). Situação diferente é observada nas proximidades do Lineamento Pernambuco, pois Ferreira et al, 2008, Lima Neto et al, 2013e Lopes et al, 2010 mostraram que a sismicidade ocorrida foi gerada pela a reativação dessa estrutura.…”