Geoscience Reference
In-Depth Information
70°W
65°W
60°W
55°W
50°W
45°W
40°W
35°W
75°W
70°W
65°W
60°W
55°W
50°W
45°W
40°W
35°W
5°N
5°N
1998
1998
(a)
(b)
GS
0°
0°
Pb
5°S
1983
1983
5°S
CBS
BP
10°S
10°S
SFC
Pc
Archean −
Mesoproterozoic
Neoproterozoic
Fold belts
Phanerozoic
Basins
magnitudes
3.0
4.0
5.0
6.0
1955
Archean −
Mesoproterozoic
Neoproterozoic
Fold belts
Phanerozoic
Basins
magnitudes
3.5
4.5
5.5
1955
15°S
15°S
TP
Pt
1964
1964
20°S
20°S
Ch
1955
1955
1985
25°S
1985
25°S
Pr
1939
30°S
30°S
1948
500 km
500 km
70°W
65°W
60°W
55°W
50°W
45°W
40°W
35°W
5°N
5°N
(c)
0°
0°
(1)
(3)
?
5°S
5°S
(2)
10°S
10°S
?
(4)
compression
(SHMax)
15°S
15°S
(5)
(6)
20°S
extension
(Shmin)
20°S
25°S
magnitudes
3.5
4.5
5.5
25°S
(7)
30°S
30°S
500 km
75°W
70°W
65°W
60°W
55°W
50°W
45°W
40°W
35°W
Figure 3.2 Intraplate epicentres in Brazil and neighbouring areas. (a) Raw catalogue, with crustal
events only (depth
<
50 km), and magnitudes
3.0. (b) “Uniform” catalogue with time-variable
magnitude thresholds. Thick solid line is the approximate limit of the Brazilian catalogue. Shading
denotes the main geological provinces in Brazil. Cratonic areas: Guyana shield (GS) and Central
Brazil shield (CBS) as part of the Amazon craton; Sao Francisco craton (SFC); intracratonic basins:
Amazon (Am), Parnaiba (Pb), Parecis (Pc), Chaco (Ch), Parana (Pr) and Pantanal (Pt); Brasiliano fold
belt provinces: Tocantins (TP), Borborema (BP), Mantiqueira (MP); SM denotes the “Serra do Mar”
coastal ranges in southeast Brazil. Dashed white areas are proposed cratonic blocks in the middle
of the Parnaıba and Parana basins. Hachured area is the Atlantic Ocean where solid line (200 m
bathymetry) denotes the edge of the continental shelf. Dates in (a) and (b) indicate magnitudes
5.3 m
b
. (c) Epicentres of the uniform catalogue (open circles) and estimates of the stress field:
grey bars are compressional principal stresses (S
Hmax
); open arrows are extensional principal stresses
(S
hmin
); numbers denote main seismic zones as discussed in Section 3.3. For colour version, see Plates
section.
