Upper crustal earthquake swarms in Sao Caetano: Reactivation of the Pernambuco shear zone and trending branches in intraplate Brazil

作者：Lima Neto Heleno C; Ferreira Joaquim M^*; Bezerra Francisco Hilario R; Assumpcao Marcelo S; do Nascimento Aderson F; Sousa Maria O L; Menezes Eduardo A S

来源：Tectonophysics, 2013, 608: 804-811.

DOI：10.1016/j.tecto.2013.08.001

• Intraplate seismicity, intraplate South America
• Focal mechanism
• Rift
• Dormant fault segment

Seismogenic fault reactivation of continental-scale structures has been observed in a few intraplate areas, but its cause is still a matter of debate. The objective of the present study is to analyze two seismic swarms that occurred along the EW-trending Pemambuco ductile shear zone and in a NE-trending branch, in 2007 and 2010 in Sao Caetano County, Northeastern Brazil. We studied both epicentral areas using a nine- and a seven-station network during 180 and 54 days, respectively. The results indicate that the 2007 swarm correspond to a right-lateral, strike-slip fault with a normal component of slip (strike 74 degrees, dip 60 degrees, and rake -145 degrees) and the 2010 swarm corresponds to a normal fault (strike 265 degrees, dip 79 degrees, and rake -91 degrees). The former reactivated a NE-trending branch, whereas the latter reactivated the main E-W-trending mylonitic belt of the Pernambuco shear zone. These results are consistent with seismogenic reactivation of this major structure, generated by the present-day EW-trending compression and NS-trending extension, as observed by previous studies. This shear zone was reactivated as rift faults in the Cretaceous during the South America-Africa breakup. However, our study confirms that the basement fabric such as continental-scale ductile shear zones, show evidence of crustal weakness outside areas of previous rifting, and it reveals the potential for large earthquakes along dormant rift segments associated with major basement shear belts.

• 出版日期2013-11-26