Shear Wave Anisotropy in the Samambaia Fault, Northeast Brazil

From May 1987 to April 1988, a 9 station, seismic network was operated near the town of Joao Camara (5°33'S, 35°51'W) in Rio Grande do Norte state, Brazil. The network was installed 6 months after the occurrence of a mb=5.1 earthquake. Shear wave splitting was observed in the Joao Camara region in all the selected events recorded by the three component station JCAZ. The polarization direction of the first split shear-wave arrival for those events lay in the north-south direction which does not agree with the premise of extensive dilatancy anisotropy for a maximum compressive stress in the east-west direction as inferred by the fault plane solutions.