| AbstractSeismicity and
stresses along the Brazilian continental margin show different patterns
between the northeastern and southeastern regions. In the northeastern
margin, earthquakes tend to occur onshore under a strike-slip regime
with horizontal compression parallel to the northern coast line. In the
southeastern margin, higher seismicity is observed offshore, in areas
where the continental crust was highly extended during the South
Atlantic rifting in the Mesozoic. Three new events in the southeast
continental shelf are shown to have reverse-faulting mechanisms, from
waveform modeling of short-period teleseismic P waves. Multiple
depth phases (reflections from the top and bottom of the water layer and
double reflections in the water layer) could be identified and better
constrained the hypocenters to middle and upper crustal depths. In South
America, models of intraplate stresses caused by plate boundary forces
and spreading effects due to the continental/oceanic crustal transition
indicate higher compressional stresses in the SE offshore area, as
compared with the continental area, in agreement with the observed
higher seismicity and reverse-faulting mechanisms. The combination of
regional stresses, local flexural effects from thick sedimentary loads,
and a presumably weaker crust from Mesozoic thinning explains the main
patterns of seismicity in the northeastern and southeastern Brazilian
margins.Return to Table of
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