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(a)
36°20'W
36°0'W
PL
0
10
20
Regional
Foliation
Shear zone
km
40°40'0"W
(b)
40°20'0"W
Shear zone
Epicenters
"
0
10
20
km
Figure 3.6 Examples of relationship of seismicity with major lineaments thought to be neotectonic
features in northeastern Brazil. (a) Focal mechanisms in the present reactivation of the Pernambuco
Shear zone (“PL” in this figure and in Figure 3.5 ) . Note that events along the main E-W branch have
E-W-trending normal faults, and events along the NE-trending branches are strike-slip because of
the E-W compressional and N-S extensional principal stresses. Focal mechanisms from Lopes et al .
( 2010 ) , Ferreira et al . (1998, 2008) and Lima-Neto et al . ( 2013 ) . (b) Earthquake sequence in a small,
E-W transcurrent fault about 10 km from the SW-NE-oriented Sobral Pedro-II Lineament (“SP-II” in
Figure 3.5 ) . The NW-SE regional maximum horizontal stress ( Figure 3.2c ) is not favorably oriented
to reactivate the major lineament, but causes seismicity in a small previously unmapped fault nearby
(Moura et al ., 2013 ) .
 
 
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