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shifted to the right of the main shock. This likewise suggests the presence of a
rigid linear structure directed across the profile. The plate motion along this
structure could trigger a cascade of destructive events at the plate edges.
P
-wave high-velocity zones in the area provide more evidence for the
existence of a rigid structure along 38° N [50, 51] (Figure 17b): ―The high-
V
patches in the megathrust zone may result from subducted oceanic ridges,
seamounts and other topographic highs on the seafloor of the Pacific plate that
become asperities, where the subducting Pacific plate and the overriding
continental plate are strongly coupled‖ [52]. Furthermore, ―a landward
extending oceanic fracture zone controlling the slab morphology change
around 38ﾰN‖ was assumed there proceeding from the lateral slip distribution
of the Tohoku event [53] and other evidence [53, 54].
As shown by the profile BB (Figure 17a) running along 38°N and across
the regional linear structure (Figure 8a), the great earthquake chain is
conformal to the junction between the Pacific and continental plates. The
compressive earthquake mechanisms correspond to the Pacific plate and its
convergence with the continent, while the normal-slip mechanisms represent
subduction-related extension. The largest event is located in the place where
the oceanic slab bends down and the plate contact is at the shallowest depth.
Figure 18. The aftershock process of the Tohoku event in space (a) and time (b),
obtained using the elliptic algorithm based on Prozorov's method [29] (a). The box
frames the study area. The curve (b) shows that the aftershock process is not over yet
(blue and red bars correspond to the number of all and
M
s
>= 2 events, respectively).
Thus, we have considered an example of primary information analysis of
seismicity by means of the GIS EEDB system using selection, sorting, and
visualization. The visualization procedures include drawing focal mechanism
solutions (beach-ball plots) in a map or in a cross section (with the vertical
