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In-Depth Information
b
N35W
S35E
Fa
Fb
F14
Fb
0
0
0
0
0
0
0
0
Y = +9 km
Y = +3 km
E1
5
5
5
5
5
5
5
5
E2
10
10
10
10
10
10
10
10
Fa
Fb
F14
0
0
0
0
0
0
0
0
Y = +6 km
Y = 0 km
5
5
5
5
5
5
5
5
10
10
10
10
10
10
10
10
Mainshock
F15 F14
0
0
0
0
Y = -3 km
5
5
5
5
4.5
5.0
5.5
6.0
6.5
7.0
Vp (km/s)
10
10
10
10
-10
-10
-10
-10
-5
-5
-5
-5
0
0
0
0
5
5
5
5
10
10
10
10
Cross-section X (km)
Figure 9.7 (b) Depth sections through the
V
p
model with superimposed relocated aftershocks dis-
tributed within
±
1.5 km of each cross-section. The white-masked areas correspond to the low-
resolution model. The contour line interval is 0.3 km/s. Dashed ellipses (E1, E2) are explained in
text. Arrows at the top of each section denote the approximate surface locations of faults.
geological fault (defined as a fault for which activity history has not been recognized since
P-wave velocities of the hanging wall in the southeast appear to be higher than those
of the footwall in the northwest. In addition, the high-
V
p
body of the hanging wall has a
slightly high
V
p
/
V
s
ratio (
1.75-1.8), while the low-
V
p
body in the footwall appears to have
alow
V
p
/
V
s
ratio (
1.6-1.7) at depths greater than 3 km in the cross-sections (see Figure 2
in Kato
et al
., 2008b). The aftershocks associated with the mainshock fault are distributed
approximately along this SE-dipping velocity boundary. Based on these observations, we
propose that the rupture of the Noto-Hanto earthquake was likely to have propagated along
these pre-existing faults. In addition to the mainshock faults, NW-dipping alignment of
