Sismicidade intraplaca em Pedra Preta (RN) no período de 2013 a 2014

Abstract

The seismic activity in Pedra Preta (RN), Northeast of Brazil, region of main intraplate seismicity of the country, began in December 2010. Before that year, there was no record of earthquakes in this area. During 2013 and early 2014, the seismo-graphic network deployed in Pedra Preta registered 273 local earthquakes in 3 or more stations. Of these, 50 events with the best readings of the arrival times of the P and S waves were selected to determine velocity model (Vp/Vs = 1.72 and Vp = 5.90 km/s) and their hypocenters were calculated, with HYPO71 software. For the determination of the composed focal mechanism, it was realized a new selection with earthquakes obeying more stringent criteria for the hypocenters (epicenters located within the network with mean arrival-time residue ≤ 0.01 s, number of observations ≥ 10, mean horizontal error < 0.1 km, mean vertical error < 0.1 km), having been selected 24 events by these criteria. The hypocenters of earthquakes show that the seismogenic fault is about 3 km long, with earthquakes between 2.3 and 5.8 km deep. The parameters of seismogenic fault were obtained by combining the method of least squares and FPFIT software (strike = 254°, dip = 67° and the rake = -66°), indicating a normal fault. The hypocenters and focal mechanism were used to verify if there was possible correlation with geological features mapped in the area and the conclusion is that there are no mapped geological features that may be directly related to the seismic activity studied.