Geography Reference
In-Depth Information
Density of seismogenic fractures
or the concentration criterion
K
avr
is a
perfectly physical parameter based on rock mechanics which describes the
seismic process in terms of fracture of solids. The respective theory was
developed by S. Zhurkov [57], and then A. Zavjalov proposed to use it for
earthquake prediction and estimated the critical value of the fracture density
parameter for the Kamchatka region [35]. P.G. Dyadkov proposed to use this
parameter for characterizing seismicity in a different way [3], namely, to
estimate the duration of seismic stability preceding a large event from
flattening of the cumulative
K
avr
plot relative to the ideal curve of uniform
fracture growth, as it was made for the Altai (Chuya) earthquake of 2003
(Figure 7).
In the case of the Tohoku earthquake, the
K
avr
curve also became flatter 6
years before the main shock, all over the nucleation area (Figure 22a). The
mapped
K
avr
patterns (Figure 22b) reveals the BB structure (Figures 16 and
17), as well as expansion of fractures toward the area of the Tohoku-event and
its foreshock.
Figure 22. Variations of fracture density (
K
avr
parameter): in time (a) and in space (b).
Black and gray colors in (a) show, respectively, real data and data corresponding to
uniform fracture growth; in (b) the grid size is 0.3 × 0.5º, 3.5 ≤
M
s
≤ 9,
H
max
= 50 km.
Thus, the application of the EEDB tools to seismicity studies in the area
around the Fukushima Prefecture allows the following inferences:
1)
There exists a rigid linear structure striking along 38°N orthogonal to
the Japan Trench and other regional tectonic lineaments;
2)
The hypothesis that the inward motion of this structure on 09.03.11 as
a result of plate boundary slip could trigger a cascade of destructive
events of 11.03.11 along its edge has been proven valid;
