Intraplate seismicity in Brazil - Intraplate Earthquakes - page 67

some areas. Stress concentration mechanisms from lateral density variations (at the edge of
cratonic keels, and from flexural deformation) seem to be very effective in mid-plate South
America. Zones of weakness are not easily defined and have not been tested properly in
this chapter. However, the higher probability of earthquakes occurring near (but not exactly
on) neotectonic faults (weak zones?) may indicate that the model of stress concentrations
near intersecting structures may also be applicable to Brazil.
While the statistical correlation of the present seismicity with geological and geophysical
features may shed some light on the mechanics of intraplate seismogenesis, especially when
similar results are found in other SCRs, one must be aware of the short time window of
the Brazilian historical and instrumental catalogue. Further studies are necessary to see if
long-term seismicity migration could help explain the lack of epicentres near geological
features that are seismically active in other areas.
Acknowledgments
We thank all the colleagues and technicians who carried out extensive field work for several
decades to study Brazilian earthquakes. Financial support frommany sources such as CNPq
(BrazilianNational Science Council), MCT (Ministry of Science and Technology), FAPESP
(Sao Paulo State Funding Agency), and many others are greatly appreciated. Most figures
were drawn with GMT (Wessel and Smith, 1998 ) ; the statistical tests were performed using
some GMT tools to select events and http://stattrek.com/online-calculator/binomial.aspx .
We thank Dan Clark and Pradeep Talwani for detailed reviews and many suggestions for
improvement.
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