SEISMICITY IN NORTH-EASTERN BRAZIL - FRACTAL CLUSTERING AND THE EVOLUTION OF THE B VALUE

We analyse a catalogue of earthquakes recorded near Joao Camara, Brazi l, an intraplate area with a simple velocity structure and low attenua tion. The evolution of seismicity is characterized by the seismic b va lue and the fractal dimension of earthquake epicentre locations measur ed from sliding 100 event windows. The events are divided into a numbe r of spatial clusters using a nearest centroid sorting technique, and two of these clusters are examined in detail. One cluster, characteriz ed by intense activity, shows a clear negative correlation between b v alue and fractal dimension of epicentre locations, as has been predict ed from simple mechanical models. A second cluster shows a weak positi ve correlation, and it is suggested that this might be explained in te rms of fluid flow in the fault zone.